case study of ganga river

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Pollution and india's living river.

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Global anthropogenic—or human caused—climate change has deeply impacted the ways that religions are practiced around the world.  At the same time, religions have also played major roles in framing the issue among their believers.  Some Hindus work tirelessly to change their habits and mitigate human impact on the climate.  Others ignore the crisis, or do not believe in Hindu environmentalism.  Read this case study with this in mind: the Hindus described here show a range of reactions to climate change, but all of them are Hindu.

As always, when thinking about religion and climate change, maintain a focus on how religion is internally diverse, always evolving and changing, and always embedded in specific cultures.

While Hinduism is a global religion, most Hindus—nearly one billion—live in India. In fact, Hindu goddesses are often a part of the Indian geographical landscape. This includes the deified river: the Ganges.

The Ganges River, also known as Ma Ganga (or Mother Ganges), flows from the glaciers of the Himalayas and crosses much of the subcontinent before flowing into the Indian Ocean. The religious origins of this goddess are varied, and devotees of different Hindu gods often believe in different stories about her. One of the more common stories comes from followers of the god Shiva. Many Shiva devotees believe Mother Ganges offered to descend to earth to purify the burning coals of the ancestors of the Hindu sage Bhagiratha. However, she was concerned that her fall from the cosmic realm would destroy the earth, so Shiva offered to catch her in his hair. Her waters ran in rivulets through his hair and onto the earth, where she purified the remains.

The Ganges River is therefore not only a waterway, but a goddess from heaven. Thus, many Hindus believe that the river has incredible healing powers. It is a common belief that bathing in the Ganges washes away a person’s bad karma and is like being in heaven. Some Hindus even believe that being brushed by a breeze which contains a single drop of the Ganges will absolve the impurities of multiple lifetimes. To most Hindus, dying in the holy city of Varanasi, on the banks of the Ganges, is said to result in moksha—a release from the endless cycle of suffering and rebirth. It is estimated that 32,000 corpses are cremated each year in Varanasi, after which their ashes are given to the Ganges. Others who cannot afford cremation simply wrap and float the body down the river. To access her healing waters, Hindus travel from all over the world on pilgrimages, often filling containers with water to bring back to their homes for rituals or healings. In fact, the largest gathering of human beings in the entire world regularly occurs on the banks of the river at the city of Allahabad. Every 12 years, the city hosts the Kumbh Mela, a religious festival during which the central ritual is bathing in the Ganges to achieve moksha. In 2001, over 30 million pilgrims attended, making it the largest gathering in human history. Unfortunately, the river has also become one of the most polluted bodies of water in the entire world, due to India’s exploding population and rapid industrialization. Over 450 million people live in the Ganges river basin, and human waste is the cause of most of the pollution. Almost five billion liters of sewage flow into the river every day, only a quarter of which is treated. By Varanasi, the Ganges is an open sewer. Fecal bacteria at this point is 150 times higher than the safe level for bathing, let alone drinking. Over 300,000 Indian children die annually from drinking contaminated water.  Industrial effluent also pollutes the river, particularly from tanneries in Kanpur. Indian industries dump nearly a billion liters of waste into the river daily. Climate change has worsened the problem: water flow has decreased as Himalayan glaciers shrink. 

In fact, many Hindus continue to bathe in or even drink the Ganges regularly. Confident in the healing powers of the divine river, they believe nothing could compromise the purity of their goddess. For them, Mother Ganges exists to wash away the impurities and pollution of earth and thus can cleanse herself. Major cleanup efforts are thus a waste of money and effort. Some governments and industries have taken advantage of these beliefs, and have used confidence in the cleansing power of the Ganges to justify continuing to pollute the river. Other Hindus acknowledge the problem, but lay blame on Muslims.  Because cattle are holy to many Hindus, Kanpur’s polluting tanneries—which create leather from cowhides—are all owned by Muslims.  Many Muslims claim that they have been unfairly persecuted by Hindu nationalists, who they say would rather persecute Muslim businesses than address more expensive sewage issues.

In March 2017, as cleanup efforts continued to fail, the High Court of Uttarakhand state confirmed the deified status that Hindus have long given the river. They issued a judgment that the Ganges and the Yamuna river—a Ganges tributary—are “living entities” which are entitled to human rights. Those caught polluting the river could thus be charged with assault or even murder. A few days later, activists sought murder charges against several politicians on behalf of the Yamuna River, sections of which are no longer able to support life. However, on July 7, 2017, the Supreme Court of India struck down Uttarakhand state’s ruling, arguing that treating the rivers as living entities was impractical. The Ganges is still revered as a living goddess by Hindus across the world, but an effective solution to its pollution remains elusive.  Hinduism Case Study – Climate Change  2018

Additional Resources

Primary sources:, secondary sources:.

•    BBC in-depth reporting on “India’s Dying Mother”: http://bbc.in/2vBdlH3  •    BBC video on the religious and geographic origins of the Ganges: http://bit.ly/2fnnhgD  •    NPR report on the Ganges as a legal “living entity”: http://n.pr/2sj02Ge  •    Financial Times video on pollution in the Ganges: http://bit.ly/2vyigrY  •    The Guardian video on pollution in the Yamuna River: http://bit.ly/2uAEIfD  •    PBS video on the Kumbh Mela festival: http://to.pbs.org/1EnPeeb  •    National Geographic video on cremations at the Ganges: http://bit.ly/2wo0SUm      

Discussion Questions

This case study was created by Kristofer Rhude, MDiv ’18, under the editorial direction of Dr. Diane L. Moore, faculty director of Religion and Public Life.

• 1.  World Religion Database, ed. Todd M. Johnson and Brian A. Grim (Boston: Brill, 2015).
• 2.  Kelly D. Alley, On the Banks of the Ganga: When Wastewater Meets a Sacred River, (Ann Arbor: University of Michigan Press, 2002), 56-60; David Kinsley, Hindu Goddesses: Visions of the Divine Feminine in the Hindu Religious Tradition, (Berkeley: UC Press, 1986), 188-189.
• 3.  Kinsley Hindu Goddesses, 191, 193-4; Justin Rowlatt, “India’s Dying Mother,” BBC News, (London), May 12, 2016. http://bbc.in/21TmEJ6 
• 4.  Linda Davidson and David Gitlitz, Pilgrimage: from the Ganges to Graceland: An Encyclopedia, (Santa Barbara: ABC-CLIO, 2002), 322-3.
• 5.  Rowlatt, “India’s Dying Mother”; George Black, “What it Takes to Clean the Ganges,” The New Yorker, Jul. 25, 2016. http://bit.ly/29PUsCy
• 6.  Krishna N Das, “India’s Holy Men to Advise Modi’s Ganges River Cleanup,” Reuters, (New Delhi), June 12, 2014. http://reut.rs/2vnJFKN 
• 7.  Rowlatt, “India’s Dying Mother.”; Black, “What it Takes to Clean the Ganges.”; Das, “India’s Holy Men.”
• 8.  Alley, On the Banks of the Ganges, 237; Kinsley, Hindu Goddesses, 191; Rowlatt, “India’s Dying Mother”; 
• Amrit Dhillon, “The Ganges: Holy River from Hell,” The Sydney Morning Herald, Aug. 4, 2014. http://bit.ly/2vQwWn6
• 9.  Black, “What it Takes to Clean the Ganges.” 
• 10.  Michael Safi, “Murder Most Foul: polluted Indian river reported dead…,” The Guardian (Delhi), July 7, 2017. http://bit.ly/2tTIGU3
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Ganga River: A Paradox of Purity and Pollution in India due to Unethical Practice

D C Jhariya 1 and Anoop Kumar Tiwari 2

Published under licence by IOP Publishing Ltd IOP Conference Series: Earth and Environmental Science , Volume 597 , National Conference on Challenges in Groundwater Development and Management 6-7 March 2020, NIT Raipur, India Citation D C Jhariya and Anoop Kumar Tiwari 2020 IOP Conf. Ser.: Earth Environ. Sci. 597 012023 DOI 10.1088/1755-1315/597/1/012023

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1 Assistant Professor, Department of Applied Geology, National Institute of Technology Raipur, Chhattisgarh-492010, India

2 Assistant Professor, Department of Humanities and Social Sciences, National Institute of Technology Raipur, Chhattisgarh-492010, India

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In India, the river Ganga is believed as a goddess, and people worship it. Despite all the respect for the river, the river's condition is worsening, and we Indians are unable to maintain the purity of the river. The Ganga is a river of faith, devotion, and worship. Indians accept its water as "holy," which is known for its "curative" properties. The river is not limited to these beliefs but is also a significant water source, working as the life-supporting system for Indians since ancient times. The Ganga river and its tributaries come from cold, Himalayan-glacier-fed springs, which are pure and unpolluted. But when the river flows downgradient, it meets the highly populated cities before merging into the Bay of Bengal. From its origin to its fall, its water changes from crystal clear to trash-and sewage-infested sludge. Thousands of years passed since the river Ganga, and its tributaries provide substantial, divine, and cultural nourishment to millions of people living in the basin. Nowadays, with the increasing urbanization, the Ganges basin sustains more than 40 percent of the population. Due to the significant contribution of the growing population and rapid industrialization along its banks, river Ganga has reached an alarming pollution level.

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• Published: 30 September 2021

Modified hydrologic regime of upper Ganga basin induced by natural and anthropogenic stressors

• Somil Swarnkar 1 ,
• Pradeep Mujumdar 1 &
• Rajiv Sinha 2  

Scientific Reports volume  11 , Article number:  19491 ( 2021 ) Cite this article

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• Environmental impact

Climate change and anthropogenic activities pose serious threats to river basin hydrology worldwide. The Ganga basin is home to around half a billion people and has been significantly impacted by hydrological alterations in the last few decades. The increasing high-intensity rainfall events often create flash flooding events. Such events are frequently reported in mountainous and alluvial plains of the Ganga basin, putting the entire basin under severe flood risk. Further, increasing human interventions through hydraulic structures in the upstream reaches significantly alter the flows during the pre-and post-monsoon periods. Here, we explore the hydrological implications of increasing reservoir-induced and climate-related stressors in the Upper Ganga Basin (UGB), India. Flow/sediment duration curves and flood frequency analysis have been used to assess pre-and post-1995 hydrological behaviour. Our results indicate that low and moderate flows have been significantly altered, and the flood peaks have been attenuated by the operation of hydraulic structures in the Bhagirathi (western subbasin). The Alaknanda (eastern subbasin) has experienced an increase in extreme rainfall and flows post-1995. The downstream reaches experience reservoir-induced moderate flow alterations during pre-and post-monsoon and increasing extreme flood magnitudes during monsoon. Furthermore, substantial siltation upstream of the reservoirs has disrupted the upstream–downstream geomorphologic linkages.

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Introduction.

Since 1901 the global average surface temperature has risen by 0.89° due to direct and indirect impacts caused by human activities on earth system processes 1 , 2 . In turn, global warming has significantly impacted the local and regional hydrological cycle worldwide 3 , 4 , 5 . Significant variability in rainfall frequency and magnitude due to changing hydrometeorological conditions has been reported across the globe 6 , 7 , 8 , 9 . As a result, severe flooding to drought conditions have become more frequent and have significantly impacted socio-economic activities in different parts of the world 10 . In addition, direct human activities such as changes in land cover, surface & groundwater withdrawal, and operations of hydraulic structures have also significantly altered the river basin hydrology in several regions 11 , 12 .

In general, dams and reservoirs play a significant role in attenuating flood peaks, frequency, duration and magnitude globally, particularly low flows 13 , 14 . Further, dams and reservoirs have also disrupted the sediment delivery to the downstream reaches, causing alteration in river channel morphology and downstream sediment starvation 15 , 16 . Consequently, river deltas are sinking at unprecedented rates worldwide 17 . Apart from the hydrological, ecological, and societal stresses caused by these large dams and reservoirs, previous researchers have also questioned their economic viability 18 , 19 .

In India, rivers largely govern freshwater resources and are considered as the lifeline of the nation. More than 70% of the rural population depends upon freshwater resources for irrigation and agricultural demands fulfilled by several large and small rivers in India 20 . However, it has been observed that the changing climatic conditions in recent decades have significantly increased the extremity of severe droughts and devastating flooding events in several parts of the country 21 , 22 , 23 . The Himalayan regions are one of the worst affected regions in the recent decades 24 , 25 , 26 , 27 . Further, several major Himalayan Rivers, particularly the Ganga River basin, are regulated by more than 300 hydraulic structures (planned, commissioned and under construction) to harness the hydropower and cater for agricultural water demands 28 , 29 . As a result, the upstream–downstream linkages of hydrological, geomorphological and ecological processes in the Himalayan River basins are severely impacted 30 , 31 , 32 , 33 , 34 . Therefore, river practitioners and scientists need to understand the implications of hydrological modifications caused by changing climate and anthropogenic activities.

In the Himalayan regions of the Ganga basin, several studies have been done to assess the impacts of land use land cover change 35 , 36 , sediment dynamics 37 , 38 , 39 , climate change hazards 24 , 25 , 26 , 40 , heavy metal 41 , water quality 42 and glacier meltwater contribution 43 . Nevertheless, detailed studies focusing on hydrological alterations caused by these hydrological structures and changing climatic conditions are currently lacking. Therefore, in this work, we select the Upper Ganga Basin (UGB) to assess the role of changing climatic conditions and increasing human activities on stream flows. The available hydrological dataset at different gauging stations was used to perform the hydrological analysis for pre-and post-dam conditions in the UGB. We first estimate the changing magnitudes of flows at those locations where large hydraulic structures were built before 1995 in the UGB. We further investigate the hydrological changes owing to changing climatic conditions and operations of hydraulic structures. Finally, we have assessed how these upstream hydrological modifications altered the hydrological regimes of the downstream regions of the UGB. The inferences drawn from the present study would be immensely useful for sustainable river basin management.

The Ganga River has two major tributaries in the upper mountainous region. The western tributary, the Bhagirathi, originates from the Gangotri glacier (30.92° N, 79.08° E) at an elevation of about 4023 m. The eastern tributary, the Alaknanda, originates from the Satopanth glacier (30.79 N, 79.37 E), an elevation of about 4600 m. At Devprayag, both tributaries join to form the Ganga. Here, we have selected the Upper Ganga Basin (UGB) up to Rishikesh (area 21,000 km 2 ) for this study (Fig.  1 a). In the Bhagirathi basin, there are four dams, namely Maneri Stage 1, Maneri Stage 2, Tehri and Koteshwar dam (Figs.  1 a, 2 a), and most of these became operational before 2010. There are only two dams in the Alaknanda basin, namely Tapovan and Srinagar, which became operational after 2015 (Fig.  1 a). Further, the Pashulok barrage is present downstream of Rishikesh. Furthermore, around 37 small and large dams are planned in the UGB (Fig.  2 b), 11 in the Bhagirathi and 26 in the Alaknanda basin 44 (Fig.  2 c,d). The mean annual rainfall in the UGB ranges from 840 to 1990 mm (Fig. S1 a). Almost 70% of the UGB receives 1000–1250 mm of rain annually, except for small patches in the western and eastern parts where more than 1500 mm of the mean annual rainfall occurs (Fig. S1 a). Overall, the Indian Summer Monsoon (ISM) contribution across the UGB varies from 51 to 86% (Fig. S1 b), leading to significant hydrological variabilities across the basin (Fig.  1 b).

(a) Digital Elevation Model (DEM) of the UGB. The major stream network is also shown in the map using magenta lines. The CWC stations and dams are illustrated using filled green circles, orange and yellow triangles, respectively. Parallel black lines show the Pashulok barrage, located below the Rishikesh. Further, the name of dams and corresponding opening year is also shown in the side table. The QGIS Version 3.2 ( https://qgis.org/en/site/forusers/download.html ) was used to generate this figure. (b) Flow duration curves (FDCs) for the period 1970–2010. The solid and dashed blue, red and green FDC lines are shown for Bhagirathi (Uttarkashi and Tehri), Alaknanda (Joshimath and Rudraprayag) and downstream stations (Devprayag and Rishikesh), respectively.

(a) Hydraulic structures in the UGB. The green and orange filled circles are showing the hydraulic structures commissioned pre-and post-2010 on the map. All these hydraulic structures’ circle sizes vary according to their hydropower generation capacity (MW). Further, A, B, C and D classes are defined based on each reservoir’s hydropower generation capacity. (b) The map shows planned hydraulic structures for the near future in the UGB. The QGIS Version 3.2 ( https://qgis.org/en/site/forusers/download.html ) was used to generate these figures. Furthermore, the bar plots show the current hydraulic structures and planned hydraulic structures for the near future in (c) the Bhagirathi and (d) the Alaknanda basin. The hill shade map of the UGB is used in the background.

Methodology

We used daily rainfall, discharge and suspended sediment load datasets for understanding the hydrological characteristics of the UGB. The details of the input dataset used in this study are listed in Table S1 (Supplementary). The exceedance probabilities were estimated in rainfall intensities, flows and sediment at each hydrological station. These estimates are depicted using the rainfall exceedance probability analysis, flow duration curve (FDC) and sediment duration curve (SDC). The daily rainfall, discharge, and suspended sediment datasets were divided into two periods—(1) 1971–1994 (pre-1995), and (2) 1995–2010 (post-1995). This temporal division was done based on the fact that the construction of a large hydraulic structure, i.e., Tehri dam (total capacity 4000 million cubic meters), started in 1995 in the Bhagirathi basin, and the frequency of flash flooding events increased in the UGB after 1995 (see Table S2 ). Hence, the anthropogenic and climate-induced alterations in the hydrology of the UGB could be captured by comparing the pre-1995 and post-1995 FDCs and SDCs. The FDCs and SDCs differences (in percentages) that showed for post-1995 were estimated with reference to pre-1995 FDCs and SDCs for all the gauge stations (see Figs. S3 and S4 in Supplementary). Further, the daily rainfall, discharge and sediments dataset for the 1971–2015 period at six stations are used for the hydrological analyses (Fig.  1 a and Table S1 ). The first five years, i.e., 1971–1975, were selected in the Bhagirathi (at Uttarkashi and Tehri) and Alaknanda basin (at Joshimath and Rudraprayag) for initial reference conditions. However, the initial reference conditions at Devprayag and Rishikesh were considered to be 1976–1980 due to the unavailability of discharge and sediments data for the 1971–1975 period. In addition, 5-yearly rainfall magnitudes, FDCs and SDCs were also estimated and compared with each station’s reference condition to assess the temporal hydrological variations. The differences (in percentage) in 5-yearly rainfall magnitudes, FDCs and SDCs were calculated by subtracting selected 5-year periods with the initial reference condition and plotted on the 2D-contour plot for each station.

We also used the frequency analysis of extreme flows (annual maximum discharge) with the Generalized Extreme Value Type-1 (Gumbel) distribution 45 at each station to estimate extreme discharge between 10- and 100-year return periods for pre-and post-1995. The Gumbel distribution for each station was selected based on Akaike Information Criterion (AIC) by comparing five widely used distributions, namely, (1) Lognormal, (2) Gamma, (3) Gumbel, (4) Weibull, and (5) Generalized Extreme Value (GEV; Table S3 ). The scale and location parameters of the Gumbel distribution were estimated using the Maximum Likelihood Estimation (MLE) method using the ‘FAmle’ package ( https://github.com/tpetzoldt/FAmle ) in R programming (see Fig. S5 in Supplementary). The differences between pre-and post-1995 extreme flows at different return periods were estimated and compared for all six gauging stations of the UGB (see Fig. S9 in Supplementary). It should be noted here that the credible extrapolation interval in flood frequency analysis is generally up to twice the record length. Hence, the 95% confidence bounds were also assessed and plotted in the return level graph for pre-1995, post-1995 and whole time series at each station of the UGB (see Figs. S6 , S7 and S8 in Supplementary).

Results and discussion

Pre-and post-1995 hydrological scenarios.

The UGB has experienced a widespread increase in high-intensity rainfall events after 1995 (Fig.  3 a,b). These are statistically increasing (p < 0.05) trends predominantly in the Alaknanda basin (Fig.  3 b). It is also noted that the Alaknanda basin has been experiencing a rising trend of high-intensity rainfall events compared to the Bhagirathi basin since 1995. The observed records also suggest an increase in extreme flooding events in the UGB (Fig.  3 c,d and Table S2 ). A total of 9 and 25 extreme flooding events are reported for the two basins together during the pre-and post-1995 period, respectively. The Bhagirathi basin has experienced 2 and 11 extreme flooding events during the pre-and post-1995 period (Fig.  3 c and Table S2 ). The Alaknanda basin has undergone 7 and 14 extreme flooding events during the pre-and post-1995 period (Fig.  3 d and Table S2 ). In terms of temperature, the Bhagirathi and the Alaknanda basins show statistically significant increasing trends. However, these increasing trends detected by the statistical tests are likely driven by the step-change that occurred between pre-and post-2000, possibly suggesting a shift in the instrumentation (Fig. S2 a,c). Further, there is no step-change or significant trend detected in the maximum temperature for both the basins (Figs. S2 b,d).

(a) Pre-and (b) post-1995 average 95th percentile rainfall magnitudes for 1970–2019. The different sizes of green filled circles represent the increasing Sen’s slope for the 95th percentile rainfall events at the 5% significance level. There is one orange-filled circle present in the Bhagirathi basin, which shows decreasing Sen’s slope for the 95th percentile rainfall events at a 5% significance level. (c,d) Shows bar plots 95th percentile rainfall of the Bhagirathi and Alaknanda basins for each year between 1970 and 2019. The blue and red bars show pre-and post-1995 annual cumulative rainfall magnitudes. The horizontal grey line shows the mean value of 95th percentile rainfall for the pre-and post-1995 period in both the bar plots. The mean (µ) and standard deviation (σ) of annual rainfall are also shown in both figures. Based on the available literature (see Table S2 in Supplementary Section), the extreme flooding events are also mentioned for the corresponding plots of the Bhagirathi and Alaknanda River basins.

In the Bhagirathi basin, the difference of post-and pre-1995 FDCs suggests a substantial reduction of up to 80% in very low flows (> 90% exceedance probability) at Uttarkashi (Fig.  4 and Table S4 ). The 5-yearly rainfall magnitude differences suggest around 50–100% reduction in low and moderate magnitude rainfall events from the reference period (Fig.  5 a). Further, the 5-yearly differences of FDCs reveal around 60–90% decline in low and moderate flows at Uttarkashi (Fig.  5 b). Coincidently, upstream of Uttarkashi, the Maneri Stage 1 dam construction was started in the 1960s, and this dam became operational in 1984 (Fig.  1 a). Therefore, a very sharp reduction in the low and moderate flows from the reference condition can be directly correlated to the operation of the Maneri Stage 1 dam. However, a decrease in the magnitude of low and moderate rainfall after 1991 (Fig.  5 a) further attenuated the low and moderate flows at Uttarkashi station (Fig.  5 b). Furthermore, the Maneri Stage 2 dam, located immediately downstream of the Uttarkashi, became operational in 2008 (Fig.  1 a), and this might have also started influencing the hydrology at Uttarkashi since then.

Difference between post-and pre-1995 flow duration curves (FDCs). These differences (%) are plotted for Uttarkashi (blue line), Tehri (dashed blue line), Joshimath (red line), Rudraprayag (dashed red line), Devprayag (green line) and Rishikesh (green dashed line) stations of the UGB. The division between high and moderate (at 20%) and moderate and low (at 70%) flows are shown by dashed black and dashed red vertical lines.

5-yearly differences in rainfall and flow duration curves (FDCs) are plotted using 2d contour plot for each station. The high (20% <), moderate (20–70%) and low (> 70%) flows are divided by black vertical lines. (a) The Uttarkashi station shows 90% reduction in low rainfall. The high rainfall slightly increased (up to 10% since 1986). (b) The Uttarkashi station shows up to 90% reduction (1981–1985) in low flows. The high flows also decreased up to 30%. (c) The Tehri station shows a reduction of 100% in low rainfall throughout the period. There is no anomalous behaviour observed in low and moderate rainfall magnitudes after 2005 at Tehri. (d) The Tehri station shows a reduction of up to 50% in low flows until 1990. After 2000, the reduction in low flows up to 85% is also appeared here. The high flows increased by 50% after 2005. The moderate flows have been increased up to 80% after 2005. (e) The Joshimath station shows increasing high, low and moderate rainfall magnitudes after 1996. The high and low magnitude rainfalls are increased up to 30% and 50%, respectively. (f) The Joshimath station shows a reduction from 20 to 70% in low and moderate flows. The high flows increased by 20% from the reference condition. (g) The Rudraprayag station shows increasing high magnitude rainfall by 30% from 1996. The moderate rainfall magnitudes have also slightly increased post-1995. (h) The Rudraprayag station shows a 10–20% reduction in all flows until 1995. The high flows have been increased 20–40% after 1995. The high rainfall magnitudes have increased up to 10% at (i) Devprayag and (k) Rishikesh stations. However, the high rainfall magnitudes have increased steeply (up to 30%) after 2005 at Devprayag than Rishikesh. The low and moderate rainfall magnitudes have decreased from the reference period at both stations. However, the percentage reductions in low and moderate rainfall magnitudes are slightly higher for the Rishikesh (up to 50%) than Devprayag (20% to 30%). The major changes in low and moderate flows up to 80% and 40% appeared at (j) Devprayag and (l) Rishikesh after 2005.

In contrast, at Tehri, the flows between 30 and 85% exceedance probability (moderate to low flows) have increased by 80% in post-1995 (Figs.  4 , 5 d) with reference to pre-1995. The difference in the FDCs of pre-and post-1995 FDCs suggests that the moderate and low flows increased rapidly downstream of the Tehri dam after becoming operational (Fig.  4 ). Additionally, the very low flows (> 90% exceedance probability) have decreased by 90% at Tehri (Fig.  5 d). The 5-yearly differences in rainfall magnitudes suggest that the moderate and low rainfall magnitudes decreased significantly after 1991 (30% to 100%; Fig.  5 c). The magnitude of very high rainfall (< 10% exceedance probability) has increased up to 30% at Tehri. In comparison, the characteristics of high and moderate flows behaviour after 1995 do not match those of high and moderate rainfall magnitudes (Fig.  5 c,d). Such anomalous hydrological behaviour of the Bhagirathi River at Tehri strongly suggests alteration of flow regime caused by the Tehri dam operation. Hence, the existence of dams in the Bhagirathi basin has reduced the extreme flows and floods downstream. Further, the moderate and low flows have significantly increased up to 125% post-2005. These abrupt increments and decrements in the flows are not observed anywhere in the UGB (Figs.  4 , 5 ). Besides, the upstream (Uttarkashi) and downstream (Tehri) stations in the Bhagirathi behave differently. These distinct and abrupt hydrological behaviour indicate the significant impact of Maneri and Tehri dams in modifying the water outflux from the Bhagirathi basin.

In the Alaknanda basin, there was no dam before 2010 (Fig.  1 a). The Srinagar dam and Tapovan dam became operational in 2015 and 2020, respectively 46 . Thus, the possibility of anthropogenically altered river flow due to reservoir operation can be ruled out before 2010. The differences in the post-and pre-1995 FDCs suggest that the high and moderate flows increased at Joshimath and Rudraprayag (Fig.  4 and Table S4 ). These differences are more predominant at Rudraprayag (up to 40%). In particular, the 5-yearly differences of FDCs from their reference condition also reveal that the high flows increased significantly after 1995 at both locations (Fig.  5 f,h). High flows at Rudraprayag show an increasing trend until 2010. However, a sudden increase (up to 100% or doubled) in high flows is observed between 1995 and 2005 for Joshimath station. The 5-yearly rainfall differences suggest increasing high magnitude rainfall after 1995 at Joshimath (up to 150%) and Rudraprayag (up to 50%; Fig.  5 e,g). It is also evident that the increasing trends (p < 0.05) of high rainfall intensities (95th percentile) have doubled (0.6 mm/y in pre-1995 and 1.2 mm/y in post-1995) and are more widespread in the Alaknanda basin (Fig.  3 b). Therefore, we argue that the increase in the high flows is linked to increasing intensities of high-intensity rainfall events in the Alaknanda basin. Further, the reported extreme events strongly suggest an increase of extreme rainfall linked to flooding events in this basin (Fig.  3 d), which have doubled (7 events in pre-1995 and 14 events in post-1995). These observations indicate that the changing climatic conditions, remarkably increasing trends of high-intensity rainfall events primarily controlled the hydrology of the Alaknanda basin until 2010. However, after the opening of the Srinagar dam (in 2015) and the Tapovan dam (in 2020; Fig.  1 a), the current flows might have been anthropogenically modified in addition to the impact of changing climatic conditions.

In the downstream reaches, high and very low flows (20% < and > 90% exceedance probability) are governed by increasing and decreasing flows from the Alaknanda and Bhagirathi basins, respectively (Fig.  4 ). However, the moderate and low flows (20–90% exceedance probability) at Devprayag and Rishikesh are predominately influenced by the moderate flows coming out from the Tehri (Bhagirathi). The 5-yearly FDCs differences at Devprayag and Rishikesh further suggest a substantial increase in moderate and low flows (> 40%), particularly after 2005 (Fig.  5 j,l and Table S4 ). However, there are no such substantial increments observed in the moderate and low rainfall magnitudes at both downstream stations (Fig.  5 i,k). These patterns strongly correlate with Tehri’s post-2005 moderate and low flows fluctuations (Fig.  5 d). Therefore, these observations suggest that the Tehri dam's water flux increased the moderate and low flows at Devprayag and Rishikesh since 2005, although these fluctuations became more significant post-2010 (Fig.  5 j,l).

Further, sediment duration curves (SDCs) suggest that high sediment fluxes are nearly similar for downstream stations. However, moderate and low sediment fluxes are an order of magnitude higher for the Devprayag and Rishikesh stations (Fig.  6 a). These differences indicate that a significant amount of sediments has been deposited between Devprayag and Rishikesh, possibly due to reduced inflow. The post- and pre-1995 differences suggest that high sediment fluxes (50% < exceedance probability) have decreased up to 50% at both locations (Fig.  6 b). These differences indicate that a considerable part of high-magnitude sediment flux is deposited upstream of Devprayag (possibly in the Tehri and Maneri reservoirs; Fig.  1 a) and not reaching the main channel downstream. Moderate and low sediment fluxes (> 50% exceedance probability) have increased tremendously at Devprayag (up to 260%) and Rishikesh (up to 70%; Fig.  6 b). These incredibly increasing amounts can be linked to sediment reworking caused by abrupt behaviour of moderate and low flows at Devprayag and Rishikesh governed by the reservoir-induced increase of moderate and low flows (Figs.  4 , 5 d,j,l). Therefore, these observations strongly suggest that the Tehri dam in the Bhagirathi basin plays a crucial role in determining the hydrological variability of the downstream UGB region.

(a) Sediment duration curves (SDCs) of Devprayag (blue) and Rishikesh (red) for the period 1970–2015. The high sediment fluxes (20% <) are comparable for both stations. However, the peak sediment fluxes are slightly higher for the Devprayag station. Further, the moderate (20–70%) and low sediment fluxes (> 70%) are an order of magnitude higher for Devprayag than the Rishikesh station. (b) Difference (%) between pre-and post-1995 SDCs of Devprayag (blue) and Rishikesh (red) stations. The peak sediment flows have been increased (120%) at Devprayag. In contrast, the peak sediment fluxes have been decreased (− 25%) at Rishikesh. Furthermore, the moderate sediment fluxes have also been reduced (up to 50%) at both stations. However, moderate and low sediment fluxes greater than 50% and 55% exceedance probability are increased from their pre-1995 values at both stations.

Role of natural and anthropogenic stressors on changing extreme flows

Frequency analysis of extreme flooding events suggests that the UGB has experienced contrasting responses due to natural and anthropogenic forcing. For instance, at Uttarkashi and Tehri, the Bhagirathi basin exhibits a total reduction of extreme flows at different return periods. Around -14.5%, -17.9% and -21.3% reductions are observed in the magnitude of 10, 50 and 100-year return period floods at Uttarkashi (Fig.  7 a,b and Table S4 ). In comparison, around -7.3%, -2.5% and -1.1% reductions are observed in the magnitude of 10, 50 and 100-year return period floods at Tehri (Fig.  7 b). Such decreasing extreme flows in the Bhagirathi basin are primarily governed by two major factors: (1) presence of small and large hydraulic structures such as Maneri Stage 1, Maneri Stage 2, Tehri and Koteshwar dam (Fig.  1 a), and (2) no significantly increasing or decreasing trends in the high-intensity rainfall events (Fig.  3 a,b).

(a) Extreme flows at different return periods at the six stations of the UGB. The Rishikesh (downstream station) and Joshimath (upstream Alaknanda basin) stations show the highest and lowest extreme flows at different return periods. The standard errors of the scale and location parameters of the Gumbel distribution are used to predict the error bound and shown using shaded regions around each return level curve. The details of 95% confidence bounds around the prediction of return level for each station are given in Supplementary. (b) Post-and pre-1995 differences of extreme flows at different return periods for different stations.

In contrast, the Alaknanda river at Joshimath and Rudraprayag show an increase of extreme flows at different return periods. For instance, around 1.5%, -0.5% and -1.1% differences are observed in the magnitude of 10-, 50-and 100-year return period floods at Joshimath (Fig.  7 b and Table S4 ). In comparison, around 15%, 9.6% and 7.9% increments are observed in the magnitude of 10-, 50-and 100-year return period floods at Rudraprayag (Fig.  7 b and Table S4 ). Therefore, the extreme flows and flooding events in the Alaknanda basin (particularly at Rudraprayag) are primarily governed by two major factors: (1) no hydraulic structures present before 2010 (Fig.  1 a), and (2) widespread increasing high-intensity rainfall in this basin (Fig.  3 a,b,d). Further, the oldest dam, Maneri Stage 1, has been operational since 1984 in the Bhagirathi basin, whereas the Srinagar dam and Tapovan dam in the Alaknanda became operational in 2015 and 2020, respectively. Therefore, we argue that the increasing number of hydraulic structures after 2015 has also impacted the extreme flows of the Alaknanda basin.

The downstream stations of the UGB behave differently when we compare the pre-and post-1995 extreme flows at different return periods. For instance, we document an increment of 10.3%, 17.5% and 19.7% in the magnitude of 10-, 50- and 100-year floods at Devprayag in the post-1995 period (Fig.  7 b and Table S4 ). However, the Rishikesh station records an -18.1% reduction in the magnitude of 10-, 50- and 100-year floods in the post-1995 period (Fig.  7 b and Table S4 ). A reduction in extreme flow magnitudes is possibly because of flow reduction caused by the Pashulok barrage downstream of the Rishikesh station. We have also observed a significant reduction in high magnitude stream flows at Rishikesh than Devprayag station (Fig.  5 j,l). The post-1995 extreme flows have decreased in the Bhagirathi basin but increased in the Alaknanda (Fig.  7 b). Therefore, a rise in extreme flooding events at Devprayag station is primarily governed by the changes in hydrometeorological conditions in the Alaknanda basin. The widespread increase in high-intensity rainfall in the Alaknanda basin and the reservoir-induced flow alterations are the primary drivers of these changes in observed extreme flow at Devprayag and Rishikesh (Fig.  3 a–c).

It is also observed that the downstream (Rudraprayag) region of the Alaknanda shows an incremental difference of up to 15% in the extreme flows (Fig.  7 b) which makes the entire downstream Alaknanda basin vulnerable to extreme flooding events in the near future. One such event was reported recently (in February 2021) near Joshimath, which destroyed the Tapovan dam 47 . Downstream of Rishikesh, the Ganga River debouches into the alluvial plains (Fig.  1 a), where several populous cities are situated. Therefore, these are the vulnerable regions where around 20% increase in extreme flooding events (at Devprayag) might enhance the flood risk manifold. Further, the Pashulok barrage downstream of Rishikesh was constructed in 1980 based on the past extreme flow information until then. However, the changing climatic conditions in the Alaknanda basin, and hence, an increase of 10–20% in extreme flows, might severely affect the operations of such structures.

Increasing anthropogenic activities and their future impacts

Overall, these hydrological analyses indicate that the flow in the Bhagirathi basin has been anthropogenically modified owing to the presence of several large and small dams (Figs.  1 a, 4 , 5 b,d). In particular, low and moderate flows, which occur primarily during pre- (Jan-May) and post-monsoon (Oct-Dec) periods, are significantly impacted (Figs.  4 , 5 b,d). The Alaknanda was a free-flowing river before the Srinagar dam was commissioned in 2015 (Figs.  1 a, 4 , 5 f,h), followed by the Tapovan dam in 2020 (Fig.  1 a,b). However, our data records could not capture these hydrological alterations at Joshimath and Rudraprayag in the Alaknanda (see Table S1 ). Recent hydrological records can be further used to verify these hydrological changes. We have demonstrated that the present low and moderate flows coming out from Devprayag and Rishikesh (downstream of the UGB) are entirely modified anthropogenically (Figs.  4 , 5 j,l). The interventions have severely affected the upstream and downstream hydrology and geomorphology of the Bhagirathi basin (Figs.  5 j,l, 6 a,b).

Around 11 and 26 additional dams of different power generation capacities in the Bhagirathi and Alaknanda basin, respectively, are planned 44 (Fig.  2 b–d). These planned hydraulic structures will be located on several small and large tributaries of the UGB (Fig.  2 b). These structures are likely to impact the low and moderate flows of the UGB further, as demonstrated in the case of the Bhagirathi basin. Additionally, the increasing number of dams will also influence the sediment transport processes across the UGB (Fig.  6 b). Further, a significant increase in the high magnitude flows is also observed in the Alaknanda River basin and Devprayag (Fig.  7 a,b). The impact of changing climatic conditions are more predominant in the Alaknanda basin (Fig.  3 a,b). Our extreme frequency analysis also suggests an increase in the magnitude of extreme flows for different return periods in the Alaknanda basin (Fig.  7 a,b). Further, the observed records indicate an increase in the frequency of extreme flood events in the UGB, especially in the Alaknanda basin (Fig.  3 a,b). During the flash flood event at Joshimath in February 2021 47 , high discharges were quickly managed because of the lean condition of the mainstream. However, if this event had occurred during the monsoon season, it could pose a severe flood risk in the downstream regions. In the past, the UGB region also witnessed the June 2013 Kedarnath disaster when rainfall magnitudes crossed a 111-year return period and produced a massive flood in the monsoon period 26 (Table S2 ). Thus, the changing extremity of streamflow in the UGB poses serious impacts on the hydraulic structures that need critical assessment and design modifications.

Conclusions

The Ganga River is the lifeline for close to half a billion people in the northern Indian region. During the twentieth century, the hydrology of the basin has been significantly modified owing to increasing anthropogenic interventions and changing climatic conditions. In particular, the upper Ganga basin (UGB) has witnessed modifications in the flow regime owing to several small and large hydraulic structures, particularly in the Bhagirathi basin (western tributary). In contrast, the Alaknanda basin (eastern tributary) has experienced increasing magnitudes of extreme rainfall events from 1970 to 2019. Therefore, the flow modifications in these basins have been influenced by different factors. Our results suggest that the reduction in rainfall magnitudes, Maneri dam in upstream and Tehri dam in downstream exert primary controls on the flows in the Bhagirathi. As a result, low and moderate flows increased at Tehri by 125%. In addition, the post-1995 extreme flows at different return periods have decreased by -21.3% in the Bhagirathi basin. Further, the Alaknanda basin was a free-flowing river until 2015. The extreme flows at different return periods have increased by 8–15% in the Alaknanda basin, primarily because of increasing high-intensity rainfall events post-1995. Therefore, the Alaknanda basin has witnessed some extreme flash flood events in recent years. Simultaneously, the downstream reaches experience anthropogenically modified low and moderate flows that are attributed to Tehri and other dams during pre-and post-monsoon months.

Our results further indicate that a significant amount of sediments transported during high flows are trapped in the Tehri and Maneri reservoirs in the Bhagirathi basin. Therefore, hydraulic structures have significantly disrupted the upstream–downstream geomorphologic linkages, thereby impacting the channel morphology in the downstream reaches as observed in several regions 48 , 49 , 50 , 51 . Furthermore, several hydraulic structures such as the Pashulok barrage were designed based on analysis of past extreme floods. However, the increasing magnitude of extreme flows (10-20%), particularly at Devprayag, might also affect the functioning of the Pashulok barrage during peak monsoon periods. The downstream regions also experience reservoir-induced flow increments during pre-and post-monsoonal months. Overall, the results obtained from this work should help in sustainable river basin management and encourage more serious work toward a better understanding of hydrology, ecology, and geomorphology in the UGB.

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Acknowledgements

The first author acknowledges the National Postdoctoral Fellowship (NPDF) grant (PDF/2020/000496) received from the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India. The second author acknowledges the support received through the JC Bose Fellowship (Number, JCB/2018/000031). The funding received from the Ministry of Earth Sciences (MoES), Government of India, through the project, “Advanced Research in Hydrology and Knowledge Dissemination”, Project No.: MOES/PAMC/H&C/41/2013-PC-II, is gratefully acknowledged. We also acknowledge the India Meteorological Department (IMD) for the high-resolution daily gridded rainfall & temperature datasets and Central Water Commission (CWC) for the daily discharge & sediment datasets provided for this work.

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S.S. analysed the hydrological records, applied the hydrological analysis and prepared the first draft of the manuscript, including figures. P.M. conceptualised the hydrological analysis, reviewed and edited the manuscript. R.S. helped to develop the hydrological analysis, reviewed and edited the manuscript.

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Swarnkar, S., Mujumdar, P. & Sinha, R. Modified hydrologic regime of upper Ganga basin induced by natural and anthropogenic stressors. Sci Rep 11 , 19491 (2021). https://doi.org/10.1038/s41598-021-98827-7

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DOI : https://doi.org/10.1038/s41598-021-98827-7

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Case Study – Ganges/Brahmaputra River Basin

Flooding is a significant problem in the Ganges and Brahmaputra river basin. They cause large scale problems in the low lying country of Bangladesh. There are both human and natural causes of flooding in this area.

Human Causes

Deforestation – Population increase in Nepal means there is a greater demand for food, fuel and building materials. As a result, deforestation has increased significantly. This reduces interception and increases run-off. This leads to soil erosion . River channels fill with soil, the capacity of the River Ganges and Brahmaputra is reduced and flooding occurs.

Natural Causes

• Monsoon Rain
• Melting Snow
• Tectonic Activity – The Indian Plate is moving towards the Eurasian Plate. The land where they meet (Himalayas) is getting higher and steeper every year ( fold mountains ). As a result, the soil becomes loose and is susceptible to erosion. This causes more soil and silt in rivers. This leads to flooding in Bangladesh.

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INTRODUCTION

River ganga: origin, expanse and cultural significance, factors responsible for changes in the dynamics of river ganga, impacts of climate change on river ganga, management aspects and research priorities, conclusions, acknowledgements, impact of climate change on the hydrological dynamics of river ganga, india.

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C. K. Jain , Surya Singh; Impact of climate change on the hydrological dynamics of River Ganga, India. Journal of Water and Climate Change 1 March 2020; 11 (1): 274–290. doi: https://doi.org/10.2166/wcc.2018.029

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Rivers provide innumerable ecosystem services to mankind. However, anthropogenic activities have inflicted a host of pressures to the riverine ecosystems. Climate change is also one of the human induced consequences which is of serious concern. A number of studies have predicted devastating effects of climate change. In the Indian context, where a river such as the Ganga is already suffering from industrial and municipal waste disposal, unhygienic rituals, and other activities, effects of climate change may further aggravate the situation. Climate change will not only result in disasters, but effects on water quality, biodiversity, and other ecological processes also cannot be denied. In this paper, an attempt has been made to evaluate the effects of climatic change on the dynamics of River Ganga. The study focuses on the impacts on fundamental ecological processes, river water quality, effect on species composition, and hydropower potential etc. The paper also discusses management aspects and research needs for rejuvenation of the River Ganga.

Climatic variability and climate change have received significant attention from the scientific community across the globe. The basic reason underlying the fact that climate change is the most discussed topic in every forum is that climate affects all the spheres which all living organisms are exposed to. The ill-effects of adverse climate change can destabilize all the facets of the environment and thereby destabilize the bonds between the abiotic and biotic components of any ecosystem. The effects of global climate change are already visible in various components of the environment – glaciers are shrinking ( Dyurgerov & Meier 2000 ) and ice is melting faster ( Gregory et al. 2004 ; Overpeck et al. 2006 ; Stroeve et al. 2007 ), sea level is rising ( Ramachandran et al. 2017 ), natural disasters such as floods, hurricanes, cyclones etc. are becoming more frequent and intense ( Easterling et al. 2000 ; Aalst 2006 ; Coumou & Rahmstorf 2012 ; Majumder et al. 2017 ), floral and faunal ranges are shifting ( Parmesan 2006 ; Wernberg et al. 2011 ), and there are also effects on agriculture and the flowering pattern of plants ( Fischer et al. 2005 ; Mall et al. 2006 ; Howden et al. 2007 ; Memmott et al. 2007 ). Almost all the ecosystems of the world are affected due to climate change. Rivers are also one of the most vulnerable ecosystems in the world. Moreover, rivers are considered as the most sensitive of all the ecosystems to the impacts of climate change, both directly and indirectly by the combination of various other stressors ( Durance & Ormerod 2007 , 2009 ). Impacts on the riverine ecosystem will not only affect the hydrology and dynamics of the river, but also pose serious threats to the survival and existence of a number of aquatic floral and faunal species, wild life, human population etc. Besides sustaining the life of organisms and providing plenty of ecosystem services, rivers are also a regulator of flood, sediment supplies, erosion, water quality and pollutant disposal etc. Mighty rivers such as the Ganga, Brahmaputra, Indus etc. also sustain many other ecosystems such as wetlands, flood plains, estuaries and riparian areas etc. by providing water, nutrients, and energy. Thus, the effects of changing climate on the river will certainly influence many other associated ecosystems too. Therefore, study of the impacts of climate change on the rivers is of utmost importance.

The impact of climate change on a river brings a plethora of consequences which affect the entire dynamics of the river, such as water resource management ( Middelkoop et al. 2001 ; Alcamo et al. 2007 ; Pahl-Wostl 2007 ; Kundzewicz et al. 2008 ), water quality ( Delpla et al. 2009 ; Whitehead et al. 2009 ), eutrophication ( Feuchtmayr et al. 2009 ; Rabalais et al. 2009 ; O'Neil et al. 2012 ), acidification ( Sabine et al. 2004 ), accumulation of toxic substances ( Gouin et al. 2013 ; Landis et al. 2013 ), hydromorphological changes ( Boon & Raven 2012 ), catchment land-use changes ( Oliver & Morecroft 2014 ), and invasion of exotic species ( Hellmann et al. 2008 ; Rahel & Olden 2008 ) etc. A number of studies on the effects of climate change on riverine systems have also been carried out ( Verghese & Iyer 1993 ; Gosain et al. 2006 , 2011 ; Boon & Raven 2012 ; Hosterman et al. 2012 ; Deshpande et al. 2016 ; Hosseini et al. 2017 ). In India, rivers play a very important role and can be even considered as the lifeline of the nation. Rivers are the main source of irrigation in the agricultural sector, upon which more than 70% of the rural population depends. Apart from this, rivers are also a major source of potable water, transportation, hydropower, aquaculture, recreational activities etc. Among the 22 river basins across the country ( CWC 2012 ), the Ganga river basin is the largest and most significant.

The River Ganga is one of the most important rivers in India. Being the largest river, Ganga supports the livelihoods of millions of people and there are many important cities and industries along its bank. However, over the years the river has faced severe negligence. Unsustainable dam construction and water diversion into the canals resulted in very low flow in the main river in several stretches. The situation further worsened due to the discharge of millions of liters of untreated industrial effluents and municipal sewage per day from nearby towns/cities. Considering the urgency of the situation and to target the escalating pollution problems, the Government of India launched an ambitious plan named the Ganga Action Plan (GAP) in 1986. However, the plan failed due to the consideration of limited issues, under-utilization of sewage treatment plants (STPs), lack of technical expertise and political will, and many other implementation issues. In 2007, the River Ganga was declared the fifth most polluted river in the world ( Rai 2013 ). To intensify the Ganga rejuvenation efforts and create more awareness regarding pollution prevention, the River Ganga was affirmed the status of ‘National River of India’ in November 2008. Later on, many other programmes were launched (e.g. Namami Gange, National Mission for Clean Ganga etc.) and various authorities were established (e.g. National Ganga River Basin Authority etc.) to revive the river, but to date the situation has not improved ( Das & Tamminga 2012 ). In such circumstances, impacts of climate change may prove to be a major setback for the river. Further, these effects may be more stringent and influential for the River Ganga considering the large area under impact. Interaction of the increasing temperature and changing discharge patterns owing to climate change, along with other existing pressures on River Ganga, will affect the survival of millions of people and various floral and faunal species. Negative impacts on other hydrological and ecological processes also cannot be neglected. Therefore, in this paper efforts have been made to assess the impacts of climate change on the various aspects of the riverine dynamics of River Ganga.

River Ganga originates from Gaumukh in the Gangotri glacier at 30°55′ N and 79°7′ E at about 4,100 m above mean sea level in the Uttarkashi district of Uttarakhand, India. The Gangetic ecosystem is one of the most vivid and complex ecosystems, on which approximately 445 million people are dependent either directly or indirectly ( Lokgariwar et al. 2014 ). The Ganga river basin is the largest among all the river basins in India, and the fourth largest in the world. The basin is part of the Ganga–Brahmaputra–Meghna basin, which drains through China (4%), Nepal (13%), India (79%) and Bangladesh (4%) ( Nepal & Shrestha 2015 ). In India, the Ganga basin lies in the states of Uttarakhand, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Rajasthan, Madhya Pradesh, Haryana, Himachal Pradesh and Delhi. In northern India, the catchment of the Ganga basin is one of the largest water catchments, draining an area of approximately 1.09 million km 2 ( Bharati et al. 2011 ). The 2,525 km river, flowing through the states of Uttarakhand and Uttar Pradesh (1,425 km), Bihar and Jharkhand (475 km) and West Bengal (625 km), touches 44% of the Indian population before flowing through Bangladesh and emptying into the Bay of Bengal ( Figure 1 ). Originating in the mighty Himalayas, the Ganga has a very fertile and large basin that accounts for 30% of India's cultivable land. In addition to its economic and ecological relevance, it also has a strong cultural presence among Indians. Nevertheless, the River Ganga is an integral part of Indian spirituality. There are many mythological statements on this river and hence, millions of Ganga devotees throng to the river just to have a holy dip ( Lokgariwar et al. 2014 ; Sanghi 2014 ). However, there is a lack of effort to understand how this massive river is responding to climate change along its basin. Climate change will have a considerable impact on the dynamics of the river Ganga. This will directly affect a major portion of northern India, which depends on the river for meeting domestic, agricultural, and industrial water needs.

Location of River Ganga.

Temperature and precipitation patterns

An increasing trend in the temperature of the Indian subcontinent is evident from the pattern shown in Figure 2 . In the coming years, the rise in temperature will be much more severe and rapid ( Diffenbaugh & Field 2013 ). According to an estimate, the average global temperature is likely to increase by 1.8–4.0 °C ( IPCC 2007 ). Rising atmospheric temperature is expected to increase the water temperature as well. Since rivers are turbulent and are in close contact with atmospheric air, they respond to atmospheric warming very quickly. It is supposed that there will be an increase in the surface water temperature of streams. Regional climate model studies in the Ganges basin predict an increase in the mean annual temperature of 1–4 °C between 2010 and 2050 ( Moors et al. 2011 ). A study on the Koshi river basin, a sub-basin of the Ganges, also reveals increasing trends in the seasonal maximum and minimum temperatures ( Shrestha et al. 2017 ). Due to the warming of climate, there may also be a change in winter precipitation from snow to rain. This eventually may lead to a change in the flow of the river ( Kundzewicz et al. 2008 ).

Trend of average annual temperature in the Indian subcontinent during 1900–2015 ( Data source: https://data.gov.in/ ).

There are other factors which also influence the river temperature and heat budget. The heating of river water depends on the amount of solar insolation received and radiated back; resistance for the heat flow offered by the river banks to the river bed; heat flow transfer between river and surrounding air, river bank, and land; evaporation and condensation mechanisms etc. Moreover, rivers also receive heat from the water coming from their catchment areas ( Webb et al. 2008 ). A combination of all these factors will influence the hydrological cycle. In response to warming climate, the hydrological cycle is expected to intensify. Since the warm air can hold more water vapor, the resulting precipitation will be much more intense. Nevertheless, due to warming climate, rainfall will replace snowfall. As drier atmospheric conditions will result in increased drying of the land surface, it will put additional pressure on the river to fulfill the water demand.

Affected by the temperature variation, precipitation is also expected to show changes ( Shrestha et al. 2017 ). Studies prove that there will be a mixed pattern of changes in precipitation – in some seasons higher rainfall may result in floods while in others extreme drought conditions may prevail due to high temperatures. Changing precipitation patterns during summer and winter are also expected to increase the nutrient loading in rivers from increased erosion of agricultural soils and associated catchment areas ( Rahman et al. 2016 ). As the pattern and intensity of precipitation will change, flow in the rivers is also expected to change. This may have a significant effect on the habitats and communities of the river ecosystem. Another impact of diminished flows is on the concentration of dissolved oxygen (DO) levels. Reduced flow conditions result in a marked decrease in DO concentration, which ultimately enhances the chances of eutrophic conditions in rivers ( Bocaniov et al. 2016 ). Higher evaporation rates coupled with reduced precipitation will lead to the continued lowering of water tables, which will eventually also lead to a reduction in groundwater levels.

High concentration of atmospheric CO 2

Exceedingly high concentrations of CO 2 may enhance the carbonic acid concentration in the river waters. The upper safe limit for CO 2 concentration in the atmosphere is considered to be 350 ppm. However, higher emission from various anthropogenic sources had increased atmospheric CO 2 concentrations to 406.82 ppm by 2017 ( Figure 3 ). Research suggests that excess CO 2 present in the atmosphere is dissolved in rainwater, resulting in the formation of carbonic acid (H 2 CO 3 ). Upon contact with rock surfaces, such waters enhance the dissolution of rock surfaces, thereby speeding up the chemical weathering processes ( Beaulieu et al. 2012 ). In the long term, this may result in much higher sediment loads on the river.

Carbon dioxide concentration in the atmosphere (1960–2017) ( Data source: Mauna Loa Observatory, Hawaii).

River Ganga is thought to carry approximately 403–660 × 10 6 tonnes of sediments annually ( Subramanian & Ramanathan 1996 ), of which 88% of the annual sediment load is restricted to only during monsoons ( Subramanian 1996 ). Therefore, further enhancement in the sediment loads will have an impact on the overall ecological characteristics as well as the water quality of the river.

Glacial retreat, runoff and river responses

The fast melting of mountain glaciers results in changes in the discharge regimes of rivers originating from glaciers ( Milner et al. 2009 ; Bliss et al. 2014 ). Glaciers influence the flow of water in rivers, as they are the natural keepers and controllers of fresh water flow to the rivers. As the increasing temperature is resulting in fast melting of glaciers, it may result in floods and other disasters in the rivers ( Lutz et al. 2014 ). Gangotri glacier in the Uttarkashi district of Garhwal Himalaya, which is the feeding glacier of River Ganga, is retreating at a fast rate owing to increasing temperature and climate change. It has been reported that the average rate of glacier retreat is 19 m/year ( Naithani et al. 2001 ). Remote sensing images reveal that this glacier has been receding since 1780; however, the retreat has increased since 1971 ( Figure 4 ). In the last 25 years of the 20th century, it has shrunk more than 850 m ( Sharma & Owen 1996 ). This will have a serious impact on the flow characteristics of the Ganga ( Bolch et al. 2012 ; Immerzeel et al. 2012 ; Kääb et al. 2012 ). It has been reported that between 2003 and 2009, approximately 174 gigatonnes of water was lost by Himalayan glaciers, which led to severe floods in the Indus, Ganga, and Brahmaputra rivers affecting millions of lives ( Gardner et al. 2013 ; Laghari 2013 ).

Retreat of Gangotri glacier (1780–2001) ( Image source: https://earthobservatory.nasa.gov/ ).

In warmer climates it is also expected that a large amount of precipitation will occur in the form of rain, rather than snow ( Trenberth 2011 ). This can have serious implications on the river water and basin area. Precipitation in the form of snow results in slow melting of ice and therefore, allows a continuous water supply to the river stream. However, rains will immediately fill up the water bodies, resulting in floods in the basin area. It has many other related consequences. Frequent rains will also result in increased soil erosion, thereby silting the rivers, which will further aggravate the flood situation ( Ghosh & Mistri 2015 ). Faster run-off from catchment areas to the river may also result in a decline in the groundwater table and soil moisture, as the over-flowing water will not have sufficient time to recharge the groundwater. In the long term, this could have very serious implications for the overall groundwater availability, soil productivity, agricultural output, and therefore on the entire population depending upon the river ( Kumar 2012 ; Kidmose et al. 2013 ; Taylor et al. 2013 ).

The changing temperature and precipitation patterns, fast glacial retreat, and increasing CO 2 concentration will have a number of subsidiary effects on the river, as discussed below.

Changes in the fundamental ecological processes

Fundamental ecological processes in any freshwater aquatic ecosystem include production and decomposition patterns, nutrient cycling, and energy flow etc. Temperature change affects the productivity of the aquatic ecosystem to a significant extent. Primary productivity may increase in response to an increase in the length of the growing season and increase in nutrient release from catchment soils. This will alter the food-web structure in river water, leading to higher phytoplankton biomass and thereby a decrease in benthic oxygen concentrations as well as an increase in nutrient release from sediments ( Jeppesen et al. 2009 ). Higher suspended sediment loads will also increase the turbidity of the river body ( Miller et al. 2015 ), therefore changing the underwater light regime. It will have adverse impacts on the growth of submerged aquatic plants. However, after some time this increasing productivity trend will begin to decline, because the rate of respiration also increases along with the increasing temperature, which again becomes a reason for increasing CO 2 . Decomposition processes also become enhanced due to higher temperatures. Once these productivity and decomposition patterns are altered, this also affects the nutrient cycling as well as the energy flow. Thus, the increasing temperature will have a significant impact on the fundamental processes of the river ecosystem.

Changes in the hydrologic characteristics of aquatic systems

Erratic rainfall patterns are not only the cause of severe floods and droughts, but are also responsible for disturbances in the discharge pattern of the river. The flow conditions of the river determine many of the characteristics, of which water quality is one. During very high discharge periods, water quality shows variations due to the mixing of waters of different origins, such as surface run-off, underground water, and water which circulates within the soil. All these waters have many different characteristics; for instance, water coming through surface run-off usually carries suspended solids along with other impurities. Water which circulates within the soil is the source of dissolved organic carbon, nitrogen, and phosphorus. Moreover, groundwater is mostly the source of silicate, calcium, magnesium, sodium, and potassium. Therefore, discharge changes lead to a change in the ambient water quality to a great extent.

River water quality

There will be colossal changes in river water quality owing to increasing temperature and global warming ( Hassan et al. 1998 ; Jun et al. 2010 ; Rehana & Mujumdar 2011 ; Todd et al. 2012 ). Increased temperature of the river water will influence the growth rate of phytoplankton, macrophytes, aquatic organisms, and other species, as many of the chemical and biological processes run at a faster pace at high temperatures. As per the Arrhenius relation, the kinetics of a given chemical reaction can be doubled for a temperature increase of 10 °C. Thus, it is expected that dissolution, solubilization, complexation, degradation and many other such effects may take place at a faster pace owing to increased temperature due to global warming. Increased temperature will also influence the growth rate of phytoplankton and bacteria ( Whitehead & Hornberger 1984 ; Wade et al. 2002 ; Sakyi & Asare 2012 ), which in turn will stimulate the process of eutrophication, thus causing the river water quality to deteriorate. Faster kinetics will also lead to faster dissociation of water molecules, thus making water more acidic. In the dry season, due to the high rate of evaporation and faster reactions, biochemical oxygen demand (BOD) will be high ( Figure 5 ). Further, irregular and intense rainfall may also result in higher run-off from the catchment area, thus resulting in higher loads of suspended solids and sediments, contaminants, and increased soil erosion ( Leemans & Kleidon 2002 ; Lane et al. 2007 ).

Impact of climatic change on water quality.

There are several water quality parameters on which climate change will have a significant impact, such as temperature, pH, DO, dissolved organic matter, micropollutants, various microorganisms etc. As stated above, an increase in temperature will lead to faster kinetics of several biochemical reactions, which will result in a concentration increase of dissolved substances and decrease in DO content. The saturation concentration of DO decreases almost 10% with a 3 °C increase ( Delpla et al. 2009 ). A decrease in DO can be linked to an enhancement in the microbial assimilation process of biodegradable organic matter, which ultimately results in dissolved organic carbon ( Prathumratana et al. 2008 ).

Dissolved organic matter is also an important factor to be considered as it affects the ecosystem functioning by influencing sunlight absorbance, energy and nutrient supply, acidity etc. Higher dissolved organic matter will result in low transparency and thus less solar penetration up to the depth of the river. It will have implications for the growth of benthic flora and fauna. In warmer climates, blue-green algae (cyanobacteria) may also flourish. It has been reported that global warming increases the total abundance and proportions of warm water species such as green algae and diatoms in the water ( Daufresne & Boët 2007 ). An increase in water temperature may also increase the pesticide concentration, as surface waters are the immediate receptors of pesticide contamination from agricultural fields. Warming climate and changes in rainfall patterns as well as intensity may also influence pesticides' ultimate fate ( Bloomfield et al. 2006 ).

Effect on species composition

As the atmospheric temperature rises, the water temperature increases as well, which ultimately affects the species diversity. Climate change is expected to affect all the levels of riverine biodiversity, from species to biome levels ( Learmonth et al. 2006 ; Bellard et al. 2012 ). As many of the species in the Gangetic ecosystem are already threatened, climate change effects will further complicate the situation. Habitat loss is expected for the species which have comparatively narrower distribution and in the locations where the temperature increase will be higher ( Eaton & Scheller 1996 ). Temperature change will also affect species composition and abundance, as well as the occurrence of scarce and/or non-native species ( Daufresne et al. 2009 ). According to Bergmann's rule of thermal regulation, species tend to be smaller in warmer climates. Therefore, a reduction in the body size of the species is also expected owing to increased water temperature.

Endemic taxa will be threatened both by habitat loss and as a result of reduced connectivity between habitats, especially if water-flow connections are lost. There is also the risk of deoxygenation due to increased temperatures. This problem can be further aggravated if there is enhancement in plant growth due to high water temperature and unlimited nutrient supply, which can lead to further low levels of oxygen and risk for the aquatic faunal species ( Whitehead et al. 2009 ). These environmental changes will further result in significant modifications in the distribution of species, higher susceptibility to alien species invasion, and overall biodiversity reduction that may eventually lead to impaired ecosystem services.

Climate change also has very negative effects on the specific biota of the River Ganga. Ganga is home to a number of fish species, reptiles, birds, and mammals. Endangered species such as the Gangetic Dolphin ( Platanista gangetica gangetica ), Ganges softshell turtle ( Nilssonia gangetica ), Gharial ( Gavialis gangeticus ), Himalayan Mahseer ( Tor putitora ) etc. are already under severe threat. These species are heading towards a higher extinction risk every passing year ( Figure 6 ). The Gangetic Dolphin, which was ‘vulnerable’ up to 1990, was moved into the ‘endangered’ category in 2004. Likewise, Gharial moved to the ‘critically endangered’ category from ‘endangered’ in 2007. Changing climate will further diminish their chances of survival. Increased temperature affects the prey population for dolphins. Changing climatic patterns may also alter the water current and flow characteristics of the river, which will further intensify the problem due to changed prey distribution, feeding grounds, changes in trophic relationships, community structure, migratory pathways, and lower reproductive success, ultimately leading to lower chances of survival ( Smith et al. 2009 ; Simmonds & Eliott 2009 ; Smith & Reeves 2012 ). For example, dolphins depend upon echolocation for finding their food; hence, changes in river flow and depth will adversely affect their distribution and survival. Warmer water may also affect the health of the river dolphins due to thermoregulatory issues and increase in exposure to toxic algal blooms.

Extinction risk of fauna in the Gangetic ecosystem.

Phenology and predator–prey interactions in riverine ecosystems

Increasing global temperature will also affect the phenology of the vegetation community as well as animals in the freshwater ecosystem ( Walther et al. 2002 ; Visser & Both 2005 ; Cleland et al. 2007 ; Anderson et al. 2013 ). While the floral community may flourish more due to rising temperatures, the consumption pattern of faunal species will also change accordingly. Temperature increase may alter the growing season, pollination, and flowering pattern of many species ( Khanduri et al. 2008 ). It will have a direct or indirect impact on the overall plant fitness ( Galen & Stanton 1991 , 1993 ). The warming temperature of water may also produce a change in the interaction patterns of algae and herbivores. Range shift is another consequence of a disturbed ecosystem. Due to changes in the surrounding water temperature, species tend to shift their ranges to a more habitable region. All the aquatic faunal species which are dependent on the phytoplankton predator–prey may not move at a similar pace to that of the phytoplankton. This mismatch may lead to a decline in some of the species ( Winder & Schindler 2004 ; Walther 2010 ). Further, over-consumption of autotrophs by herbivores can disturb the entire ecosystem, as climate change can also result in changes in the feeding pattern of many species owing to the changes in food availability and requirements ( Stenseth et al. 2002 ). Increased water temperature will also lead to changes in the food-web structure, with higher winter survival of fish and a general switch from dominance of zooplankton and aquatic macrophytes to fish and phytoplankton. In rivers, increased temperature will cause stress for fish and invertebrates with high oxygen requirements, leading to changes in community composition. The population of some of the aquatic faunal species may also face the danger of extinction if the physiological processes are not able to be in sync with the phenological changes.

A change in predator–prey interactions is another significant repercussion of climate change ( Abrahams et al. 2007 ; Broitman et al. 2009 ). In the Gangetic ecosystem, the fish community, fish-eaters, and their prey are ectothermic. Therefore, a change in the surrounding water temperature will influence the energy needs or food requirements of these species. Higher temperature results in faster metabolism, leading to a higher energy requirement; this refers to increased interactions between predator and prey. The influencing parameters of the water affecting predator–prey interactions will be temperature, DO, and turbidity ( Abrahams et al. 2007 ). It has been shown in Figure 5 that under elevated water temperature conditions, DO will be decreased while turbidity will be enhanced. In the reduced DO concentration conditions, many of the prey species would try to avoid being predated by deliberately moving towards hypoxic environments. Thus, a hypoxic environment will act as a shelter for the prey species and a barrier for the predator ( Figure 7 ). Turbidity will have its impact on the process of prey detection by predators and subsequent survival efforts of the prey species. Due to the turbid water conditions, prey will become unable to mark the presence of its predator well ahead of time ( Figure 7 ), and hence the chances of its survival will reduce ( Miner & Stein 1996 ).

Predator–prey interaction: (a) effect of DO, (b) effect of turbidity.

Hydropower potential of the river

As hydroenergy is solely dependent on water resources, climate change impacts on rivers will certainly affect the hydroenergy potential of India ( Pathak 2010 ). India is the seventh largest producer of hydroelectric power in the world. By 2017, India's installed hydroelectric power capacity was about 13.5% of the total power generation capacity ( GoI Report 2017 ). The River Ganga is known to support a number of hydropower projects in approximately 10 states of the country, the highest being in the state of Uttarakhand. Moreover, the Ganga basin will have the highest dam density in the Himalayan region if all the ongoing and proposed dams are constructed ( Pandit & Grumbine 2012 ). Therefore, it is necessary to understand the impacts of climate change on the hydropower potential of River Ganga. In hydropower production, the amount of electricity generated in a dam/reservoir is dependent on the quantity of the water passing through the turbine, the water head, and the mechanical efficiency of the turbine. Water passing through the turbine further depends on the seasonal and quantitative changes in precipitation pattern and evapotranspiration ( Koch et al. 2011 ). Therefore, changes in climate resulting in variability in temperature, precipitation and run-off will certainly have an impact on the hydropower potential of the dams and reservoirs. Besides reservoirs, the run-off-river hydropower potential will also be disturbed to a great extent. A number of case studies have been carried out in the past depicting the negative impacts of climate change on overall hydropower production ( Madani & Lund 2010 ; Chiang et al. 2013 ; Kachaje et al. 2016 ; Tarroja et al. 2016 ). Basically, climate change will influence hydropower production through two variables: discharge and head. Variation in the discharge pattern of the river may disturb the continuous water availability to power stations. Whereas less discharge is expected to reduce the power production, high discharge for a few months followed by a longer dry period may result in increased spill, thereby again rendering decreased power generation. Reduced precipitation events will also reduce the required head level in the reservoirs, as low inflow will result in lower water levels. Moreover, variation in temperature and precipitation intricately influences a number of factors, which ultimately result in reduced hydropower production, as depicted in Figure 8 . Negative impacts on the hydropower generation owing to variable climate will certainly have an effect on the entire scenario of the energy sector. In such situations, dependency on existing conventional fossil fuels may increase, which will further contribute to climate change.

Impact of climate change on hydropower production.

The above discussion reveals that undoubtedly, climate change impacts will prove to be disastrous not only for the river but also for the millions of people who are directly or indirectly dependent on it. In order to attenuate the impacts, significant efforts are required to be undertaken. A proactive approach is essential to find suitable ways of dealing with the situation. Research into the dynamic aspects of a riverine ecosystem, stormwater management, river catchment management, aquatic ecology and related features is essential. Further, accepting the fact that climate change is already taking place, adaptive approaches also need to evolve. Although rivers, being dynamic entities, are continuously adapting themselves, current climate changes are occurring at a much faster rate than the adaptive capability of the rivers. Moreover, a reactive approach is the ultimate solution to overcome the impacts due to climate change-induced disasters. Thus, a combination of these approaches will hopefully bring resilience to the dynamics of River Ganga ( Figure 9 ).

Management strategy for the River Ganga.

Changes in the basic hydrological aspects of the river would influence many of the related ecological processes such as energy flow pattern, biogeochemical cycles, productivity in the riverine ecosystem, decomposition processes, predator–prey interactions, inter-specific competition etc. ( Traill et al. 2010 ). In order to sustain ecological processes, it is imperative to identify the key species that are responsible for the ecosystem's resilience. It has been found that high species richness is able to sustain the ecosystem very well under stressed conditions ( Loreau et al. 2001 ); therefore, those species which are known to have lesser functions may prove to be highly beneficial in the longer term. Considering these facts, more research needs to focus on the assessment of species diversity in the Gangetic ecosystem. In order to assess the threats to the Gangetic ecosystem, continuous research is also necessary for finding the response of aquatic floral and faunal species towards various extrinsic factors. More emphasis should be given to finding the processes and mechanisms through which changes are taking place in the behaviour, physiology, and evolution of species along with mechanisms affecting intra- and inter-specific relations. In order to avoid range shifting of various micro- and macrospecies of the Gangetic ecosystem, research is required to understand the life history and ecology of the species ( Palmer et al. 2009 ). It is imperative to say that in dynamic riverine ecosystems, the effects of change may sometimes also be reversed by various ecosystem processes ( Suttle et al. 2007 ).

In order to attenuate the adverse impacts of climate change, a number of adaptive management strategies also need to be adopted in the Ganga basin. Existing causes of stress in the river, such as point and non-point pollution, water abstraction, increasing number of dams/reservoirs etc., need to be curtailed. There is a need to enhance and strengthen the conservation measures also, not only for the river but also for the adjacent catchment area. Plantations along the riparian area may help to slow down the silting and flood situation. The establishment of drought tolerant plant species may also help to prevent erosion of the river bank in high temperature conditions. Moreover, appropriate environmental flow needs to be maintained in the Ganga, especially in the middle and lower reaches, so that the river may recuperate. Invasive plant species which can threaten the native species should be removed. There is also a need to know the features at gene, population, community, and ecosystem levels which may provide better chances of survival to the organisms. Apart from adopting various protective measures for the river, significant efforts are also required to control allied activities such as forestry and related land uses, grazing, farming, dam/reservoir management etc. ( Arthington et al. 2006 ).

As already stated, severe rainfall resulting from extreme weather events may lead to floods and subsequently significant erosion of river banks and catchment areas. Therefore, river restoration projects need to be executed well ahead of time to avoid grave consequences. In order to reduce high energy flow and for improvement in river water quality, additional water bodies may be created as storage basins, which will be adjacent to the Ganga river and have linkages with the main channel. Wetland creation and the development of storm water infrastructure may also result in a positive outcome ( Poff 2002 ). For better preparedness and quick response action, strengthening of water monitoring networks and weather forecasting systems is essential. River flow monitoring on a regular basis is also essential to determine the climate change-induced alterations in flow pattern ( Palmer et al. 2009 ). There should also be efforts for the management of nearby land areas, and anthropogenic activities should be minimized. Infrastructure development and industrial agglomeration along the river need to be curtailed in order to lessen the pollution load in the river.

Another very significant aspect in the management of the river is effective policy planning. Past experiences show that due to lack of coordination among various monitoring agencies involved, the expected results could not be achieved. As the River Ganga flows through five states, coordinated efforts are required to execute any plan. Besides the involvement of a central agency, state boards and municipal authorities should also be involved. Public participation is also essential in governing water-related issues. Thus, a decentralized approach to planning is vital for the effective implementation of schemes and positive outcomes.

Conservation and management of the River Ganga is a national priority ( Figure 10 ). Since time immemorial it has been the most revered river in the country. Besides providing a host of ecosystem services, the River Ganga has also played a very important role in the growth and development of the economy by contributing to the agricultural sector, industrial sector, hydropower generation, tourism, and other recreational activities. However, due to increased urbanization and industrialization, there has been a colossal loss in the pristine quality of the river. The effects of climate change will further add to the pitiable condition of the river and in coming years, these risks will be much more intense. Climate change impacts will not only result in severe disasters of floods and drought, but will also reduce the carrying capacity as well as assimilative capacity of the river by affecting its abiotic and biotic components. Therefore, immediate efforts are required in order to reduce any further degradation of the river ecosystem. Despite a number of action plans executed in the past few decades, there is still much to be done. More concerted efforts are required in the direction of climate change management. Plans related to the control of pollution in the River Ganga need to be intermingled with climate change management efforts by employing better policy planning. There is also a need to learn from the experiences gained in the past. Moreover, bridging the gap between scientific/technical interventions and spiritual consciousness can be an effective step for the rejuvenation of the River Ganga.

Impact of climate change on the dynamics of River Ganga.

The authors are grateful to the Department of Science and Technology, New Delhi, India for financial support (Grant No. DST/SPLICE/CCP/NMSHE/TF-4/NIH/2015-G).

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Pollution of River Ganga, Case Study

Pollution of the Ganges (or Ganga), the largest river in India, poses significant threats to human health and the larger environment. Severely polluted with human waste and industrial contaminants, the river provides water to about 40% of India's population across 11 states, serving an estimated population of 500 million people which is more than any other river in the world. Today, the Ganges is considered to be the sixth-most polluted river in the world. Raghubir Singh, an Indian photographer, has noted that no one in India spoke of the Ganges as polluted until the late 1970s. However, pollution has been an old and continuous process in the river as by the time people were finally speaking of the Ganges as polluted, stretches of over six hundred kilometres were essentially ecologically dead zones. A number of initiatives have been undertaken to clean the river but failed to deliver as desired results. After getting elected, India's Prime minister Narendra Modi affirmed to work in cleaning the river and controlling pollution. Subsequently, the Namami Gange project was announced by the government in the July 2014 budget.[10] An estimated Rs 2,958 Crores (US$460 million) have been spent until July 2016 in various efforts in cleaning up of the river. Background of the case Ganga is a trans-boundary river of Asia flowing through India and Bangladesh. It is one of the most sacred rivers to the Hindus and a lifeline to a billion Indians who live along its course. One of the most populated cities along its course is Kanpur. This city has a population of approx. 29.2 lakhs (2.9 million). At this juncture of its course Ganga receives large amounts of toxic waste from the city´s domestic and industrial sectors, particularly the leather tanneries of Kanpur. In 1985, M.C. Mehta filed a writ petition in the nature of mandamus to prevent these leather tanneries from disposing off domestic and industrial waste and effluents in the Ganga river. This writ petition was bifurcated by the Supreme Court into two parts known as Mehta I and Mehta II. Mehta I [ M.C. Mehta v. Union of India , [1987] 4 SCC 463]: Proceedings and Orders passed before final judgment: In this petition the petitioner requested the court to request the Supreme Court (the Court) to restrain the respondents from releasing effluents into the Ganga river till the time they incorporate certain treatment plants for treatment of toxic effluents to arrest water pollution. At the preliminary hearing the Court directed the issue of notice under Order I Rule 8 of the CPC, treating this case as a representative action by publishing a small gist of the petition in the newspapers calling upon all the industrialists, municipal corporations and the town municipal councils having jurisdiction over the areas through which the river Ganga flows to appear before the Court and to show cause as to why directions should not be issued to them. In pursuance of this notice many industries and local authorities appeared before the Supreme Court. The Court highlighted the importance certain provisions in our constitutional framework which enshrine the importance and the need for protecting our environment. Article 48-A provides that the State shall endeavor to protect and improve the environment and to safeguard the forests and wild life of the country. Article 51-A of the Constitution of India, imposes a fundamental duty on every citizen to protect and improve the natural environment including forests, lakes, rivers and wild life. The Court stated the importance of the Water (Prevention and Control of Pollution) Act, 1974 (the Water Act). This act was passed to prevent and control water pollution and maintaining water quality. This act established central and stated boards and conferred them with power and functions relating to the control and prevention of water pollution. Section 24 of the Act prohibits the use of the use of any stream for disposal of polluting matter. A stream under section 2(j) of the Act includes river, water course whether flowing or for the time being dry, inland water whether natural or artificial, sub-terrene waters, sea or tidal waters to such extent or as the case may be to such point as the State Government may by the notification in the official gazette may specify. The Act permits the establishment of Central Boards and State Boards. Section 16 and Section 17 of the Act describe the power of these boards. One of the functions of the State Board (the Board) is to inspect sewage or trade effluents, plants for treatment of sewage and trade effluents, data relating to such plants for the treatment of water and system for the disposal of sewage or trade effluent.

What is a Trade Effluent?

Mehta ii (m.c. mehta v. union of india decided on 12th january, 1988).

• (iii) the collection and removal of sewage, offensive matter and rubbish and treatment and disposal thereof including establishing and maintaining farm or factory:
• (vii) the management and maintenance of all Mahapalika waterworks and the construction or acquisition of new works necessary for a sufficient supply of water for public and private purposes.
• (viii) guarding from pollution water used for human consumption and preventing polluted water from being so used.

The Court also relied on Section 251, 388, 396, 398, 405 and 407 of the Adhiniyam which provide provisions for disposal of sewage, prohibition of cultivation, use of manure, or irrigation injurious to health, power to require owners to clear away noxious vegetation and power of the Mukhya Nagar Adhikari to inspect any place at any time for the purpose of preventing spread of dangerous diseases. These provisions deal with the duties of the Nagar Mahapalika or the Mukhya Nagar Adhikari appointed under the Adhiniyam with regard to the disposal of sewage and protection of the environment. These provisions governing the local bodies indicate that the Nagar Mahapalikas and the Municipal Boards are primarily responsible for the maintenance of cleanliness in the areas of their jurisdiction. The Court also relied on the provisions of the Water Act which provide the meaning of pollution, sewage effluent, stream and trade effluents. Sections 3 and 4 of the Water Act provide for the establishment of the Central and State Boards. A State Board was constituted under Section 4 of the Water Act in the State of Uttar Pradesh. Section 16 of the Water Act sets out the functions of the Central Board and Section 17 of the Water Act lays down the functions of the State Board. The functions of the Central Board are primarily advisory and supervisory in character. The Central Board is also required to advise the Central Government on any matter concerning the prevention and control of water pollution and to co-ordinate the activities of the State Boards. The Central Board is also required to provide technical assistance and guidance to the State Boards, carry out and sponsor investigations and research relating to problems of water pollution and prevention, control or abatement of water pollution. The functions of the State Board are more comprehensive. In addition to advising the State Government on any matter concerning the prevention, control or abatement of water pollution, the State Board is required among other things:

• to plan a comprehensive programme for the prevention, control or abatement of pollution of streams and wells in the State and to secure the execution thereof;
• to collect and disseminate information relating to water pollution and the prevention, control or abatement thereof;
• to encourage, conduct and participate in investigations and research relating to problems of water pollution and prevention, control or abatement of water pollution;
• to inspect sewage or trade effluents, works and plants for the treatment of sewage and trade effluents;
• to review plans, specifications or other data relating to plants set up for the treatment of water, works for the purification thereof and the system for the disposal of sewage or trade effluents or in connection with the grant of any consent as required by the Water Act;
• to evolve economical and reliable methods of treatment of sewage and trade effluents, having regard to the peculiar conditions of soils, climate and water resources of different regions and more especially the prevailing flow characteristics of water in streams and wells which render it impossible to attain even the minimum degree of dilution; and
• to lay down standards of treatment of sewage and trade effluents to be discharged into any particular stream taking into account the minimum fair weather dilution available in that stream and the tolerance limits of pollution permissible in the water of the stream, after the discharge of such effluents.

Sections 20, 21 and 23 of the Water Act confer power on the State Board to obtain information necessary for the implementation of the provisions of the Water Act, to take samples of effluents and to analyze them and to follow the procedure prescribed in connection therewith and the power of entry and inspection for the purpose of enforcing the provisions of the Water Act. Section 24 of the Water Act prohibits the use of stream or well for disposal of polluting matters etc. contrary to the provisions incorporated in that section. Section 32 of the Water Act confers the power on the State Board to take certain emergency measures in case of pollution of stream or well. Where it is apprehended by a Board that the water in any stream or well is likely to be polluted by reason of the disposal of any matter therein or of any likely disposal of any matter therein, or otherwise, the Board may under Section 33 of the Water Act make an application to a court not inferior to that of a Presidency Magistrate or a Magistrate of the first class, for restraining the person who is likely to cause such pollution from so causing. The Court relied on a common law principle which states that Municipal Corporation can be restrained by an injunction in an action brought by a riparian owner who has suffered on account of the pollution of the water in a river caused by the Corporation by discharging into the river insufficiently treated sewage from discharging such sewage into the river. In the case of Pride of Derby and Derbyshire Angling Association v. British Celanese Ltd [3], the Derby Corporation admitted that it had polluted the plaintiffs fishery by discharging into it insufficiently treated sewage. According to the Derby Corporation Act, 1901 it was under a duty to provide a sewerage system, and that the system which had accordingly been provided had become inadequate solely from the increase in the population of Derby. The Court noted that M.C. Mehta is not a riparian owner. Nevertheless he is a person interested in protecting the lives of the people who make use of the water flowing in the river Ganga. Therefore, his right to maintain the petition cannot be disputed. The nuisance caused by the pollution of the river Ganga was held to be a public nuisance. Final judgment:

• The Court directed the Kanpur Nagar Mahapalika to take appropriate action under the provisions of the Adhiniyam for the prevention of water pollution in the river. It was noted that a large number of dairies in Kanpur were also polluting the water of the river by disposing waste in it. The Supreme Court ordered the Kanpur Nagar Mahapalika to direct the dairies to either shift to any other place outside the city or dispose waste outside the city area.
• Kanpur Nagar Mahapalika was ordered to increase the size of sewers in the labour colonies and increase the number of public latrines and urinals for the use of poor people.
• Whenever applications for licenses to establish new industries are made in future, such applications shall be refused unless adequate provision has been made for the treatment of trade effluents flowing out of the factories.

The above orders were made applicable to all Nagar Mahapalikas and Municipalities which have jurisdiction over the area through which the Ganga river flows. In addition to this, the Supreme Court further relied on Article 52A (g) on the Constitution of India, which imposes a fundamental duty of protecting and improving the natural environment. The Court order that:

• It is the duty of the Central Government to direct all the educational institutions throughout India to teach at least for one hour in a week lessons relating to the protection and the improvement of the natural environment including forests, lakes, rivers and wildlife in the first ten classes.
• The Central Government shall get text books written for the said purpose and distribute them to the educational institutions free of cost. Children should be taught about the need for maintaining cleanliness commencing with the cleanliness of the house both inside and outside, and of the streets in which they live. Clean surroundings lead to healthy body and healthy mind.

Training of teachers who teach this subject by the introduction of short term courses for such training shall also be considered. This should be done throughout India. Written By:- Navnit Kumari

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Analysis and pollution assessment of heavy metals in suspended solids of the middle stretch of river Ganga between Kanpur to Prayagraj, U.P., India

• Published: 14 November 2023
• Volume 48 , article number  257 , ( 2023 )

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• Mohit Aggarwal 1 , 2 ,
• S Anbukumar 2 &
• T Vijaya Kumar 2  

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In this study, suspended solids samples were collected from 10 locations along the 225 km stream of Ganga River amidst Kanpur and Prayagraj city during July 2021 to assess heavy metal contamination. The average values of studied metal concentrations were found in the following order: Fe (51939 µg/g) > Mn (1048 µg/g) > Cr (129 µg/g) > Zn (215 µg/g) > Ni (69.5 µg/g) > Pb (71.8 µg/g) > Cu (68.9 µg/g) > Cd (1.70 µg/g). Risk Analysis was done using pollution indicators. Contamination factor average values lie between 0.62 and 1.17 indicating moderate contamination by Zn, Pb and Cd and less contamination by other metals. Geoaccumulation Index (Igeo) values indicate moderate contamination by Cu and Cr metal (Igeo > 0) at some sites. The average value of enrichment factors (EF) lies between 0.71 and 1.35 indicating no enrichment of Mn and minor enrichment of other metals. Pollution Load Index (PLI) lies between 0.69 and 1.30 indicating progressive deterioration at some sites. Nawabganj and Manikpur sites were plotted out as the most contaminated sites. Anthropogenic content and Lithogenic contribution were determined which identified anthropogenic input of Zn, Pb and Ni at all sites. Statistical analysis was done using a correlation matrix and Principal Component Analysis (PCA) which showed a strong correlation of Cu with Zn and Ni. Observed heavy metal concentrations were compared with averages of other world rivers. The increased levels of Zn, Cd, and Pb may have resulted from the tannery and paint industries of the upstream Jajmau industrial area and also because of excessive use of pesticides and fertilizers which should be taken seriously to prevent further increase in heavy metals concentrations.

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Aggarwal, M., Anbukumar, S. & Kumar, T.V. Analysis and pollution assessment of heavy metals in suspended solids of the middle stretch of river Ganga between Kanpur to Prayagraj, U.P., India. Sādhanā 48 , 257 (2023). https://doi.org/10.1007/s12046-023-02325-7

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Received : 27 June 2023

Revised : 19 September 2023

Accepted : 27 September 2023

Published : 14 November 2023

DOI : https://doi.org/10.1007/s12046-023-02325-7

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