Using groundwater to adapt to climate change and increase water security

MacDonald, Alan

Using groundwater to adapt to climate change and increase water security

MacDonald, Alan ORCID: https://orcid.org/0000-0001-6636-1499. 2025 Using groundwater to adapt to climate change and increase water security. [Keynote] In: 10th International Groundwater Conference, Roorkee, India, 5-7 Mar 2025. (Unpublished)

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Abstract/Summary

From the earliest times, the use of groundwater has been critical for human life and sustaining and growing livelihoods. Access to groundwater has solved many water security issues through the centuries, and since the second half of the 20th century has helped underpin growth in many countries (Re at al. 2022). In this 21st century there are new challenges to contend with. Human influence has increased the chance of compound extreme climate events with more frequent and intense heatwaves, droughts and heavy precipitation. With every increment of global warming, changes in extremes and the associated risks and impacts will escalate, becoming increasingly complex and difficult to manage (IPCC 2023). With this growing variability and uncertainty in both the volume and timing of precipitation, demand for groundwater is increasing rapidly with half the earth’s population now dependant on groundwater for their drinking water (UN 2022). Groundwater resources are already being used by households, farmers, industry and municipalities to adapt to increases in weather variability – and further changes in climate are likely to increase the use of groundwater for adaptation. This poses the question - how resilient is groundwater to climate change? Will it continue to provide the water security required by households, cities and nations? There are three factors that help determine intrinsic groundwater resource resilience (Foster & MacDonald 2014): aquifer storage volume, transmissivity (permeability) and long-term recharge. Groundwater in larger aquifer systems have long residence times and response times, meaning that their large natural storage can buffer short term changes in climate, while low storage aquifers which provide good yields in normal years, can begin to suffer in droughts if demand is high. With changes in the modality of precipitation, thinking of groundwater recharge over the long term becomes more important – recharge may not occur every year, but become more episodic (Cuthbert et al, 2019). Other sources of recharge, for example from rivers, and canals can also increase the resilience of a groundwater system to change (e.g MacAllister et al, 2022) but are rarely accounted for. Finally, how easily groundwater flows within the aquifer (transmissivity), is often a controlling factor on whether individual wells and tubewells dry up during a drought period – there can be groundwater within the aquifer, but the cone of depression around the individual tubewell reduces the flow from the aquifer to the pump. These three intrinsic factors, combined with the anthropogenic forcing of water demand and pollution, help to characterise and forecast how groundwater can support adaptation to climate change and provide increased water security. Within India, groundwater is used extensively to buffer existing climate variability, and the aquifer conditions markedly influence water security. The Indo-Gangetic Basin Aquifer is one of the most productive aquifers in the world and is marked by its large storage and active recharge (MacDonald et al. 2016). Therefore, with some notable exceptions, it has largely been able to cope with the high demands put on it by the >10 million tube wells. The high permeability of the aquifer also means that the yield of individual tube wells change little from season to season, and only tube wells in areas suffering long term depletion are subject to declining yields. Long term recharge to the aquifer system is highly complex and can be contested. Recharge from rainfall is more or less predictable, and dependent on the Indian Monsoon, however river flow (mostly indirectly through canal leakage) is likely to provide much of the long-term groundwater recharge, particularly in less humid areas. This spatially and temporally dynamic for groundwater recharge is impacted by climate change: directly through changes to the Indian Monsoon; indirectly through glacial melt and river flow; and management of reservoirs and canal irrigation. In contrast, the low storage crystalline aquifers of Peninsular India offer much less resilience to climate change, rendering groundwater a risky solution to water insecurity. Long term monitoring in the Cauvery Catchment has shown that groundwater levels can progressively decline due to high demand, which depletes the more productive parts of the aquifer, resulting in tubewells which have lower yields, and some shallow sources drying up altogether. Occasional heavy monsoon seasons can replenish the aquifers, meaning that long-term depletion is less of an issue, however the aquifers are more susceptible to short term drought. Drilling deeper here is rarely the answer, as the aquifers become less productive and have less storage capacity at depth. The widespread use of managed aquifer recharge may impact highly localised water security, but there is little evidence that it makes a regional impact here. So can groundwater be managed to help adapt to climate change and increase water security? Firstly, it is important to know how much is being used and by whom. For example, recent research is showing that many urban dwellers in the world have access to groundwater as a backup for when a municipal system fails, but this groundwater use is rarely recorded. Then 3D knowledge and mapping of aquifers, and monitoring of groundwater dynamics and trajectories helps identify where the opportunities for groundwater development are, and where boundaries are at threat of being exceeded, or may already have been surpassed. But this knowledge alone will not effect change. A deep and nuanced understanding of the science-policy-practice framework is required to help effect change that will be long lasting – including an understanding of what makes groundwater knowledge useful, usable and accepted (Milman and MacDonald 2020).

Item Type:

Publication - Conference Item (Keynote)

Additional Keywords:

IGRD, GroundwaterBGS

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