Several studies and reports published during 2024 have underlined the rising adverse impacts of changing climate on groundwater resources in India and globally in multiple ways which will continue to accelerate in future. While the groundwater greatly contributes to river baseflows during lean period, its role in flooding is miniscule comparatively with surface flows in Peninsular India. In North India the drying northwest monsoon and warmer winters have been found driving groundwater depletion by raising demand for irrigation water.
The groundwater is getting warmer, also impacting subterranean aquatic ecosystems. Besides, the rising temperatures are causing more evaporation losses and leading to pumping of more groundwater to compensate for the losses. The extreme rainfall events might speed up fertilizers seeping into groundwater table contaminating it. Similarly, the rising sea level is found fueling erosion in coastal areas and facilitating seawater intrusion of the coastal aquifers. At the same time the decline in low and medium intensity rainfall and warmer weather patterns are reducing groundwater recharge, increasing seawater ingress.
Climate change and human activities have also extensively been impacting recharge, discharge, flow, storage and distribution of groundwater. Apart from studies on these issues, there are some interesting studies and reports on estimating groundwater recharge methods, using changes in groundwater levels to forecast earthquakes.
1. Majority of global river flow sustained by groundwater Abstract: Groundwater-sustained baseflow is a vital source of river flow, especially during dry seasons. The proportion of river flow sustained by baseflow—the baseflow index—is essential for assessing fluvial nutrient cycling and contaminant transport. However, the global baseflow index remains highly uncertain, with current Earth system model simulations ranging from 12% to 94%. This paper estimates the global baseflow index to be 59% ± 7% based on an emergent constraint approach, which integrates 50 Earth system models with baseflow indices derived from streamflow observations in 15,567 basins.
The observational constraint indicates that at least 21% ± 3% of precipitation recharges groundwater, which is approximately double the figure reported in the Sixth Assessment Report of the United Nations Intergovernmental Panel on Climate Change. Thus, this research suggests a more active role of groundwater in the global water cycle than most Earth system models currently simulate. This paper presents evidence that the considerable disagreement in simulated baseflow stems from unrealistic and varied model representations of infiltration, aquifer structure and groundwater dynamics. These processes should be prioritized so that models can capture active groundwater–river connections. https://www.nature.com/articles/s41561-024-01483-5 (19 July 2024)
‘Baseflow among most important factors driving river flooding in Peninsular India’ This is the first study (https://www.nature.com/articles/s41598-024-51850-w), to use observed discharge data from Indian river basins to enhance our understanding of the process-based factors influencing river floods.
Trends in the annual mean baseflow showed a pattern similar to trends in flood magnitudes, indicating a relatively strong correlation. In contrast, rainfall and soil moisture trends were less consistent with flood trends, resulting in a weaker correlation. These findings suggest that multi-decadal trends in baseflow have had a significant impact on trends in flood hazards in Peninsular India. The paper examined the relationship between annual floods and their drivers for antecedent periods ranging from 1 to 14 days. Baseflow is the dominant factor for shorter time lags, while rainfall plays a more significant role at longer antecedent periods. A catchment with higher baseflow indicates wetter conditions, leading to an increased likelihood of rapid runoff with incoming rainfall events.
The paper examined the correlation between floods and baseflow on the flooding day and the days leading up to it to further validate the findings. Across Peninsular catchments, a high positive correlation was observed five days before the flood event, reinforcing the strong influence of baseflow on floods. To understand what happens to this association on the flooding day, the authors investigated the relative contribution of baseflow to peak flows using the Baseflow Index (BFI). A negative correlation was observed between flood magnitudes and BFI, indicating that while baseflow contributes more to river flows, its share in the event flow magnitude decreases as surface runoff accounts for a larger proportion of flood discharge on the day of the flood. Moreover, a flood event cannot occur without substantial rainfall, even if the landscape has high baseflow. https://www.downtoearth.org.in/interviews/water/-baseflow-one-of-most-important-factors-driving-river-flooding-in-peninsular-india–95864 (29 Apr 2024) The study throws light on the role of groundwater contribution to baseflow in rivers and their flooding in Peninsular India’s rivers like Narmada, Tapi, Mahanadi, Godavari, Krishna and Cauvery. The authors found that while baseflow contributes more to river flows, its share in the flood event flow magnitude decreases as surface runoff accounts for a larger proportion of flood discharge on the day of the flood.
The study is not only very useful in its own right, but it also underlines the need for many more studies on Rivers in India, one of the least studied subjects. One of the reasons for such studies not being done or delayed, as pointed out in the study is the non-availability of stream flow data in public domain. It is high time that the govt and Central Water Commission make these public promptly on daily basis. https://sandrp.in/2024/05/06/drp-nb-060524-study-on-dam-induced-river-flooding-in-peninsular-india/ (6 May 2024)
2. Changing nature of groundwater in global water cycle Abstract: In recent decades, climate change and other anthropogenic activities have substantially affected groundwater systems worldwide. These impacts include changes in groundwater recharge, discharge, flow, storage, and distribution. Climate-induced shifts are evident in altered recharge rates, greater groundwater contribution to streamflow in glacierized catchments, and enhanced groundwater flow in permafrost areas. Direct anthropogenic changes include groundwater withdrawal and injection, regional flow regime modification, water table and storage alterations, and redistribution of embedded groundwater in foods globally. Notably, groundwater extraction contributes to sea level rise, increasing the risk of groundwater inundation in coastal areas. The role of groundwater in the global water cycle is becoming more dynamic and complex. Quantifying these changes is essential to ensure sustainable supply of fresh groundwater resources for people & ecosystems. https://www.science.org/doi/10.1126/science.adf0630#sec-2 (1 Mar 2024)
Global water cycle is off balance for the 1st time Decades of destructive land use and water mismanagement have collided with the human-caused climate crisis to put “unprecedented stress” on the global water cycle, said the report published Oct 16 by the Global Commission on the Economics of Water, a group of international leaders and experts.
The report differentiates between “blue water,” the liquid water in lakes, rivers and aquifers, and “green water,” the moisture stored in soils and plants. While the supply of green water has long been overlooked, it is just as important to the water cycle, the report says, as it returns to the atmosphere when plants release water vapor, generating about half of all rainfall over land. Disruptions to the water cycle are “deeply intertwined” with climate change, the report found.
A stable supply of green water is vital for supporting vegetation that can store planet-heating carbon. But the damage humans inflict, including destroying wetlands and tearing down forests, is depleting these carbon sinks and accelerating global warming. In turn, climate change-fueled heat is drying out landscapes, reducing moisture and increasing fire risk. https://edition.cnn.com/2024/10/16/climate/global-water-cycle-off-balance-food-production (16 Oct 2024)
New warnings from studies about global water changes A number of reports throw fresh light on functioning of global water cycle, some of the findings should be seriously worrying. The studies show how the countries across the globe have water connections that go far beyond shared rivers, lakes and seas. And how these components of global water cycles are not only changing but are under unprecedented stress and could take the global water cycles off balance. https://sandrp.in/2024/10/21/drp-nb-21×24-new-warnings-from-studies-about-global-water-changes/ (21 Oct. 2024)
3. How can we better track groundwater recharging? Researchers in Darwin recently undertook the largest analysis to date of long-term rainfall recharge across Australia. They used 98,000 estimates of recharge rates, using data from bores and machine learning algorithms. The result was surprising. They estimated the average recharge rate for the Australian continent was just 44 mm/ year. But it differs a great deal. In humid, wet climates such as across the Top End, the water table rose by 203mm a year. But in arid climates, it was just 6mm. The typical annual rainfall in Sydney & Brisbane is just over 1,000mm.
This study poses a challenge to our understanding of groundwater recharge. The estimates in this study are substantially lower than studies relying on contemporary water balance models, which report more than double the amount of recharge for Australia. One issue is the Darwin research was not able to show where the groundwater came from or how old the water is. You might think groundwater recharges quickly, but a quick recharge means it takes years. A slow recharge can take thousands of years.
This gap is a concern. Our water authorities need the most accurate data possible on annual recharge rates – and the age of the water. Our network of hydrological loggers are now gathering underground data in sites such as the gold mine in Stawell, in Victoria, and South Australia’s Naaracoorte Caves, famous for fossils, as well as mines and tunnels in New South Wales, Queensland and Tasmania.
Natural caves and groundwater are often fairly shallow. We wanted to get deeper data, which is why we chose mines. Our deep sites are over 100 metres underground. Our sensors can detect each groundwater recharge event by doing something very simple: counting drips from the ceiling, and comparing them to what’s happening on the surface, so we can see where and when groundwater recharges. https://theconversation.com/how-quickly-does-groundwater-recharge-the-answer-is-found-deep-underground-230943 (25 June 2024)
Model developed to estimate GW recharge more accurately A study published in the Hydrology and Earth System Sciences journal of European Geoscience Union (EGU) in April 2024 talked about the estimation of groundwater recharge at a country level. The study was led by Stephen Lee from the Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Australia. The study has used 200,000 groundwater chloride measurements to estimate groundwater recharge rates using chloride mass balance (CMB) method across Australia.
CMB is used to quantify the recharge rates for groundwater wells in a dry environment using the chloride content of both precipitation and groundwater. Researchers clearly indicate that the factors which influence the groundwater recharge rate are both climate and vegetation related. The climate-related variable includes the rainfall distribution, evapo-transpiration, whereas, the vegetation-related factors include the health and density of the vegetation.
Soil properties and the geographic variation also influence the rate of groundwater recharge but can be ranked as low influencers, according to the researchers. The study established that it is very important for any modelling of groundwater recharge rates to consider the change in land-use pattern. https://www.downtoearth.org.in/news/water/australian-researchers-develop-model-to-estimate-groundwater-recharge-more-accurately-95766 (24 April 2024)
GW recharge is sensitive to changing long-term aridity Abstract Sustainable groundwater use relies on adequate rates of groundwater recharge, which are expected to change with climate change. However, climate impacts on recharge remain uncertain due to a paucity of measurements of recharge trends globally. This paper leverages the relationship between climatic aridity and long-term recharge measurements at 5,237 locations globally to identify regions where recharge is most sensitive to changes in climatic aridity. This is in regions where potential evapotranspiration slightly exceeds precipitation, meaning even modest aridification can substantially decrease groundwater recharge.
Future climate-induced recharge changes are expected to be dominated by precipitation changes. Recharge is more sensitive to changes in aridity than global hydrological models suggest. Consequently, the effects of climatic changes on groundwater replenishment & their impacts on the sustainability of groundwater use by humans & ecosystems probably exceed previous predictions. https://www.nature.com/articles/s41558-024-01953-z (12 Mar 2024)
Rapid groundwater decline & some cases of recovery This paper compiles and analyses in situ measurements of groundwater-level trends in about 170,000 monitoring wells. The measurements provide new constraints on the prevalence of rapid and accelerating groundwater-level declines and their correlation with land use and climatic drivers. Furthermore, the measurements highlight individual cases in which groundwater levels have recovered following policy changes and inter-basin water transfers. https://www.nature.com/articles/s41586-023-06879-8#Sec1 (24 Jan. 2024)
4. Cryosphere–groundwater connectivity a missing link in mountain water cycle Abstract: The mountain cryosphere and groundwater play pivotal roles in shaping the hydrological cycle, yet their connectivity remains incompletely understood. Current knowledge on meltwater recharge and consequent groundwater discharge processes is better developed for snow–groundwater connectivity than for glacier–groundwater connectivity. Estimates of meltwater recharge vary considerably, which is probably a function of not only inherent catchment characteristics but also of the different spatio-temporal scales involved and the uncertainties in the methods used. This hinders a comprehensive understanding of the mountain water cycle. As glaciers retreat, permafrost thaws and snowpack diminishes, the relative importance of mountain groundwater is expected to increase. However, shifting and declining recharge from the cryosphere may decrease absolute groundwater amounts and fluxes with as-yet unknown effects on catchment-scale hydrological processes. We therefore stress the need to better quantify mountain cryosphere–groundwater connectivity to predict climate change impacts on mountain water supply and to support sustainable water resource management of downstream socio-ecological systems. (Paper needs subscription) https://www.nature.com/articles/s44221-024-00277-8 (19 July 2024)
5. Saltwater will taint 77% of coastal aquifers by 2100 Seawater will infiltrate underground freshwater supplies in about three of every four coastal areas around the world by 2100, according to a recent study led by researchers at NASA’s Jet Propulsion Laboratory in Southern California. In addition to making water in some coastal aquifers undrinkable and unusable for irrigation, these changes can harm ecosystems and corrode infrastructure.
Two impacts of climate change are tipping the scales in favor of salt water. Spurred by planetary warming, sea level rise is causing coastlines to migrate inland and increasing the force pushing salt water landward. At the same time, slower groundwater recharge—due to less rainfall and warmer weather patterns—is weakening the force moving the underground fresh water in some areas.
The study published in Geophysical Research Letters in Nov 2024 evaluated over 60,000 coastal watersheds around the world, mapping how diminished groundwater recharge and sea level rise will each contribute to saltwater intrusion, estimating what their net effect will be. https://phys.org/news/2024-12-saltwater-taint-coastal-aquifers-century.html (11 Dec 2024)
6. Extreme weather could increase risk of GW contamination This study, published in the journal Water Resources Research, found that sudden bursts of water from heavy rains following a drought caused nitrates — a component of nitrogen fertiliser — to seep 33 feet, or 10 metres, in as little as 10 days. “The conventional wisdom was that it could take several weeks to years for nitrates to move from the crop root zones to reach groundwater,” corresponding author Isaya Kisekka, a professor at the University of California – Davis, US, said, “We found these extreme events, such as California’s atmospheric rivers, are going to move nitrate more quickly”.
Previous studies have shown that about 40 % of nitrogen fertilisers used for vegetables is not absorbed by the plants but remains in the soil. During droughts, crops do not use nitrogen efficiently, leading to excess nitrogen in the soil. Using conservation practices that limit leftover nitrates in the crop’s root zone after harvest could help farmers reduce groundwater contamination. Affordable tools for monitoring nitrates in soil real-time can help farmers manage the use of fertilisers efficiently, Kisekka said. https://timesofindia.indiatimes.com/science/extreme-weather-could-increase-risk-of-groundwater-contamination-study-finds/articleshow/115333473.cms (15 Nov. 2024)
7. Rising temp threaten tiny animals responsible for GW quality A new study compared temperatures inside 12 caves around the world with their respective surfaces, showing that average annual temperatures in underground systems tend to mirror those of the surface, but with far less variation. The researchers also found that while some caves follow outdoor temperatures with little or no delay, others have temperatures that are very asynchronous with the surface, being at their warmest when the world outside is at its coldest, and vice versa.
Scientists also detected the existence of daily thermal cycles in the deepest sections of some caves, suggesting that such cycles might mark the circadian rhythms of cave-adapted organisms. The results indicate that underground fauna — with many species ill-adapted to handle large temperature variations — might be at threat due to climate change, and that their extinction might risk the water quality of aquifers worldwide.
Just like the underwater depths, science still knows precious little about this vast kingdom that all of us, unsuspectingly, live above. And much of what we do know is due to a basic human need: water. Some scientists are turning their attention to how rising temperatures might impact underground ecosystems themselves. And for that, they’re using the most accessible doorway we have into the world below: caves. https://news.mongabay.com/2024/03/rising-temperatures-threaten-the-tiny-animals-responsible-for-groundwater-quality/ (18 Mar 2024)
Groundwater to get warmer The “world’s first global groundwater temperature model” predicted the highest warming rates in Central Russia, Northern China and parts of North America, and the Amazon rainforest in South America. Warming of groundwater can adversely impact ecosystems relying on them. “Rivers rely on groundwater to keep flowing during dry times. Warm waters hold less dissolved oxygen,” explained study co-author Gabriel Rau from the University of Newcastle, UK.
Based on how heat spreads in water, the researchers modelled current groundwater temperatures and also projected changes during 2000-2100 around the world. Warmer groundwater raises the risk of disease-causing microbial growth, thereby, affecting drinking water quality and potentially the lives of people, said Rau. Warmer groundwater can also impact water quality by affecting its chemistry and microbiology, they said. https://www.telegraphindia.com/india/groundwater-to-get-over-3-degree-celsius-warmer-by-centurys-end-threatening-safety-study/cid/2024819 (5 Jun 2024) This article delves into the effects of climate change on the potability of groundwater, the causes, and potential solutions. https://www.counterview.net/2024/09/researchers-note-severe-impact-of.html (8 Sep 2024)
8. 100,000-year journey of groundwater tracked A new study mapped continental groundwater flow, revealing that rain and snowmelt travel much farther and deeper underground than previously known. Published on Jan 6 2025 in the journal Nature Water, the study shows that more than half of the water flowing in rivers and streams originates from deep aquifers once considered isolated from surface water systems. These findings carry significant implications for managing groundwater resources, tracking pollution, and predicting how climate change might affect groundwater—an essential source of drinking water for half of the U.S. population.
This study’s new retrospective analyses and predictive simulations provide opportunities to track this vital resource and understand the far-reaching impacts of leakages from the likes of oil and gas well pads. “Interconnections between the watersheds isn’t just important for streamflow,” said Maxwell. “This also tells us how long contamination will persist in groundwater. Widespread pollutants like nitrate and PFAS can take these long journeys to the stream, making them harder to manage and even longer-lived.”
The second important new discovery of Maxwell’s team is that deep groundwater from aquifers 10 to 100 meters below the surface contributed more than half of the baseflow in 56% of the subbasins. The greatest depths occurred in regions with the steepest topography gradients, such as the Rocky and Appalachian mountain ranges. https://scitechdaily.com/new-study-tracks-the-100000-year-journey-of-underground-water/ (11 Jan. 2025)
9. Groundwater pumping has tilted Earth’s rotation by 31.5 inches Over less than two decades, our groundwater pumping has tilted the Earth by 31.5 inches. To put this into perspective, this water redistribution equates to approximately 0.24 inches of sea-level rise. The study, which included data from 1993 through 2010, showed that pumping as much as 2,150 gigatons of groundwater has caused a shift in the Earth’s tilt. The study is published in the journal Geophysical Research Letters.
“Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole,” said Ki-Weon Seo, a geophysicist at Seoul National University. We may not think about where our water goes after we use it, but most of it ends up being transported to the oceans. “Observing changes in Earth’s rotational pole is useful for understanding continent-scale water storage variations,” said Seo.
Unlike the water you see in rivers and lakes, groundwater is hidden away, acting like nature’s hidden water bank. It plays a crucial role in the water cycle, providing a steady supply of water even during dry spells when surface water might be scarce.
The new revelations about groundwater pumping open new doors for our understanding of climate change and our capacity for action. It is imperative to balance human needs with environmental conservation, which requires innovative approaches to water usage, such as enhanced irrigation systems, rainwater harvesting, and improved municipal water management. Furthermore, global cooperation among countries is essential to create comprehensive policies that address the equitable distribution and consumption of water. https://www.earth.com/news/our-everyday-water-use-is-literally-tilting-the-earth/ (24 Nov 2024)
10. Forecasting earthquakes using changes in GW chemistry Abstract An advance has been made towards a method for forecasting earthquakes several months before they occur. The method relies on changes of groundwater chemistry as earthquake precursors. A study in 2014 showed that changes of groundwater chemistry occurred prior to and were associated with two earthquakes of magnitude 5 and higher, which affected northern Iceland in 2012 and 2013. This paper tests the hypothesis that similar or larger earthquakes could have been forecast in the following decade (i.e. 2014–2023) based on our published findings. It found that we could have forecast one of the three greater than magnitude 5 earthquakes that occurred. Noting that changes of groundwater chemistry were oscillatory, it infers expansion and contraction of the groundwater source region caused by coupled crustal dilation and fracture mineralisation associated with the stress build-up before earthquakes. It concludes by proposing how this approach could be implemented elsewhere. https://www.nature.com/articles/s43247-024-01852-3 (06 Nov. 2024)
11. GW depletion up in North India under climate change Summary The decline in summer monsoon precipitation and warmer winters have resulted in a loss of groundwater between 2002 and 2021. Rapid groundwater depletion (∼1.5 cm/year) resulted in a net loss of 450 km3 of groundwater during 2002–2021. This necessitates the implementation of groundwater sustainability measures to ensure future agricultural production. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024EF004516 (6 Aug 2024) Examining the response of India’s groundwater to the warming climate is critical for climate adaptation and ensuring food and freshwater security. https://www.thehindu.com/news/national/telangana/study-shows-accelerating-groundwater-depletion-in-north-india/article68487352.ece (5 Aug 2024) The depletion is about 37 times the quantity of water the Indira Sagar dam — India’s largest reservoir — can hold at full capacity, lead author Vimal Mishra, Vikram Sarabhai Chair Professor of Civil Engineering and Earth Sciences at IIT Gandhinagar, said. The team comprised of researchers from the National Geophysical Research Institute-Hyderabad. https://www.business-standard.com/india-news/north-india-lost-nearly-450-cubic-km-of-groundwater-in-2-decades-study-124070700117_1.html (07 July 2024)
Compiled by Bhim Singh Rawat (bhim.sandrp@gmail.com)
SANDRP 