Almost all liquid freshwater globally is groundwater. Groundwater supports irrigated agriculture, provides drinking water, and sustains ecosystems. Groundwater recharge, the rate at which new water replenishes underground aquifers, is crucial in determining whether these aquifers can be used sustainably because it limits how much groundwater can be abstracted over long periods.
Excessive human groundwater use is depleting many aquifers worldwide. Groundwater accessibility could be further threatened by climate change. However, how climate change will alter groundwater recharge remains uncertain.
Groundwater response to climate
Existing estimates of global groundwater recharge are uncertain because measurements to test these estimates are sparse. “We bring together climate data and measured groundwater data from thousands of field sites worldwide to study the effects of climate directly from measurements”, explains Ype van der Velde, hydrologist and co-author of the article that was published in Nature Climate Change. “By doing so, we can improve the reliability of our estimations of the effects of climate change on groundwater resources.”
The work shows that, across many regions, future recharge changes are stronger than previously estimated, and expected to be dominated by climate-change-related rainfall changes rather than directly via temperature. The data also indicate that changes in groundwater recharge will be relatively larger than precipitation changes.
The rate of groundwater recharge will increase in the northern latitudes of Europe, Asia and the Americas, Southeast Asia, West, Central and East Africa, and Argentina. At the same time, many regions already struggling with groundwater depletion will receive less groundwater recharge in a warmer world. This will exacerbate existing groundwater challenges.
Groundwater effects on floods and droughts
Groundwater also affects floods and droughts. A recent study published in the scientific journal Environmental Research Letters, also led by VU earth scientist Wouter Berghuijs, shows that often flood changes are strongly shaped by long-term changing groundwater conditions. “We need to better acknowledge this coupling between ground and surface waters”, says Berghuijs. “This is crucial to predict how this natural hazard is changing”. Investigating this coupling between groundwater and surface waters will be the focus of two new projects, one supported by a Starter Grant provided by the Ministry of Education, Culture, and Science and through the RESHAPE Project funded by NWO-KIC.