Climate Change and Groundwater Resources in South Asia

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Diesel Pumping Set Extracting Water from a Shallow Tube Well for the Paddy Crop on the Outskirts of Dhaka, Bangladesh (Photo: Dr. Niladri Gupta, 2022)

Climate change has brought about increased temperature and shifts in precipitation patterns around the world, impacting the water resources sector.

The IPCC’s sixth assessment report (AR6) highlights that changes in extremes have been observed, causing extreme weather events such as heatwaves, heavy precipitation, droughts, and tropical cyclones due to global warming.

Continued global warming is projected to further intensify the global water cycle, spreading its variability, global monsoon precipitation pattern, and the severity of wet and dry events, impacting availability of water resources and their management throughout the world.

Groundwater is an important component of the freshwater regime for agriculture, drinking water supplies, and sustaining ecosystems.

It modulates the temperature and baseflow of rivers, lakes and wetlands; regulates exchanges of nutrients and minerals; and prevents land subsidence and seawater intrusion.

Groundwater, often unseen and neglected, holds immense promise in our adaptation to climate change and needs to be judiciously managed.

According to the United Nations World Water Development Report 2022 (UNWWDR 2022), which uses 2017 data, the global rates for withdrawal of freshwater exceeds 3,881 km3 per year, with groundwater contributing about a quarter of the total withdrawal.

Estimates show that about 959 km3 (959 trillion liters) of groundwater were withdrawn in 2017, out of which 69 percent was for agriculture, 22 percent for domestic and 9 percent for industrial use.

Groundwater is important, for agriculture – food production and security, while domestic use, though smaller in volume, is critical for survival. Almost 50 percent of the global urban population depends on groundwater as the primary source for drinking water and its societal importance far outweighs the volume of extraction.

Figure 1: Groundwater Withdrawal Volumes and Its Share in Freshwater Withdrawal in the Continents (Data from UNWWDR, 2022)

Sound groundwater management actions need to be implemented to better safeguard this vital resource

Asia withdraws the highest volume of freshwater: 2,505 km3 every year, of which 657 km3 is groundwater. This represents about 69 percent of the total world groundwater extraction.

These figures are large for Asia, due to its large population and water-intensive agricultural practices in the region. Groundwater withdrawal in South Asia alone is about 401 km3 per year.

Groundwater is a spread resource, available where there is an aquifer and providing direct access to consumers. It is generally of a high quality, and is not directly impacted by rainfall variability.

It is also less polluted than surface water. This poses opportunities for exploitation as well as constraints in the management of this valuable resource.

Water resources management, on a broad scale, requires information on future water availability and requirements of a finer temporal and spatial resolution, to decide on new projects as well as on the operation and maintenance of existing systems.

The existing and future needs and demands are both affected by climate change at the river-basin and local scales. It is certain that the future demands on groundwater and reliance on this resource will increase due to the increasing uncertainty of surface water.

Surface water is directly impacted by climate change and its ushering in of extreme events, more intense rainfall and floods, along with extended periods of drought which create water stresses.

This will potentially increase the rates of groundwater extraction, lowering water tables of already-stressed aquifers.

The direct impacts of climate change on groundwater is still the subject of research. The recharge of aquifers takes place via widespread “evaporation-surplus” rain as well as express recharge pathways such as leakage from rivers, ephemeral streams, wetlands, or lakes. Groundwater systems respond at a slower pace to climate change than surface-water systems.

Rising temperature reduces water available for infiltration by evaporating more water from the surface, soil profile, and even, shallow aquifers, enhancing soil salinity and raising the temperature of shallow groundwater, with possible repercussions on the physio-chemical properties of water.

Conceptual Representation of Key Interactions between Groundwater and Climate (Taylor et al., 2013)

Variabilities in rainfall affect groundwater differently. It is commonly believed that in humid areas, intense rainfall of a shorter duration limits the time available for infiltration; top soil remains saturated during precipitation and a higher portion of rainfall is partitioned into runoff, thus reducing groundwater recharge.

Variations in aquifer recharge not only change the aquifer yield or discharge, they can also modify the groundwater flow network; e.g. gaining streams may suddenly become losing streams, groundwater divides may change position.

It should be noted that the effect of climate change on groundwater is often impacted by indirect effects, introduced by anthropogenic choices in response to adapting to climate change.

In mountainous areas, snow and glacier melt generally dominate mountain hydrology. Groundwater contribution to runoff can be significant during the spring and the dry season, providing a perennial or seasonal groundwater supply to mountainous springs and ecosystems.

Melting snow, permafrost and glaciers provide a steady water supply for infiltration in the near future, while the distant future could face water scarcity due to the absence of these storages of water.

Climate change impacts are often blamed for a reduction in the flow – or even the drying-up – of springs in Nepal, as well as in Sikkim, in the Eastern Himalayas; but these could be complicated by anthropogenic reasons including land use changes.

The alteration of groundwater quality due to overextraction or polluted runoff including contaminants from fertilizers, pesticides, herbicides or municipal wastes such as pharmaceuticals and personal care products (PPCPs), perfluoroalkyl and polyfluoroalkyl substances (PFAs) and even sewage leakages, are all issues that need to be strictly controlled and managed to assure the sustainability of this vital resource.

It should be understood that climate change’s effects on groundwater are amplified by our actions. The net effect of climate change on groundwater depends not only on changing climatic conditions but also on the physical characteristics of a region, human actions and management decisions.

Sound groundwater management actions need to be implemented to better safeguard this vital resource and enhance our adaptive capabilities, with a better understanding of the impacts of climate change and human interventions on groundwater.

The CARE for South Asia project is carrying out the scoping study on impact of climate change on groundwater resource in Nepal in to better understand the ground realities and the necessity for planning ahead.

The writer is Water Resources Management Specialist in Nepal at ADPC and can be reached at: laxman.sharma@adpc.net

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paul

paul@abu.org.my

http://wpx2.abu.org.my/

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Exploring the Impacts of Climate Change on Groundwater Resources

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paul

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