Groundwater flowing within the geology beneath our feet is the. Its volume in most countries in Africa for example, which flows annually through their rivers, lakes and wetlands. The widespread distribution and inter-annual storage of groundwater play an essential role in sustaining ecosystems and enabling adaptation to climate variability and change. The original review, , was borne, in part, out of frustration with the near absence of groundwater in reports discussing climate change impacts on water resources and the hydrological cycle by the Inter-governmental Panel on Climate Change (IPCC). 25 co-authors and I sought to publish a scientific consensus addressing these shortcomings in advance of the that could not be overlooked.
Seven years later, theremains a relevant, comprehensive treatise on the interactions between groundwater and climate change. Two key developments since amplify points made in the original review. First, a bias in groundwater replenishment to extreme (heavy) rainfall has now been more widely observed in tropical and sub-tropical regions. Second, evidence from the has revealed more clearly large-scale changes in groundwater storage and the magnitude of uncertainty in global models simulating groundwater recharge and the impacts of climate change.
As the planet warms,in where, when and how much rain and snow will fall. One consistent, observed impact of global warming is , , which results in fewer light rain events and more frequent, heavy rainfalls. The consequences of this changing distribution in precipitation globally are serious and include reduced soil moisture, more frequent and intense floods as well as longer and more frequent droughts. Evidence of a ‘silver lining’ in these changes comes from and a , which show a distinct bias in groundwater replenishment to heavy rainfall, often in association with large-scale controls on climate variability such as – Figure 1. This bias in groundwater recharge to heavy rainfalls has similarly been noted in and . Increased use of groundwater consequently becomes a logical strategy to adapt to climate change impacts on water resources.
Figure 1: Flood discharge during the 2015-16 El Niño event in central, semi-arid Tanzania, replenishing the wellfield that is the sole supply of water to its rapidly growing capital, Dodoma.
GRACE satellite monitoring from 2002 to 2016 reveals large-scale depletion of groundwater from unregulated human withdrawals,. Quantification of groundwater depletion globally from GRACE data and models has helped . Further, GRACE satellite data have provided a sobering test of global-scale models of terrestrial water balances, . Lastly, new insight into large-scale climate-groundwater dynamics has been gained from GRACE data that includes and .
The importance of groundwater as a climate-resilient source of freshwater in the 21st century is difficult to overstate. Climate-driven shortages in freshwater supplies to the cities ofand led to a substantial, subsequent rise in their dependence upon wells. As the world warms, amplification of rainfall extremes and its consequences will be most pronounced in the tropics where, by 2050, . Yet it is here where substantial increases in freshwater withdrawals are required to achieve (SDGs) of enhancing food security through irrigation (SDG 2) – Figure 2 - and rapidly expanding access to safe water (SDG 6) – Figure 3.
Figure 2: Dry-season irrigation of boro rice using groundwater in central Bangladesh.
Figure 3: Deep well supplying freshwater surrounded by the saline surface waters in the Sundarbans of Bangladesh.
Developing water supplies resilient to climate change will, in many parts of world, invariably involve use of groundwater conjunctively with rivers, lakes, and reservoirs. There is much to be done in terms optimising conjunctive use of these sources including recognition that Please join us.and that . Beyond advancing our understanding of groundwater and its interactions with climate and surface waters, much more needs to be done and . On-going, inter-disciplinary research programmes and are informing progress here but considerably more investment and effort are required. In recognition of the critical importance of groundwater to climate change adaptation and need to find pathways towards sustainable groundwater use globally, . It has now been signed by over 1200 scientists and practitioners from 99 countries.