Ground water and climate change

1 Ground water is an almost ubiquitous source of generally high-quality fresh water. These characteristics promote its widespread development, which can be scaled and localized to demand, obviating the need for substantial infrastructure1. Globally, ground water is the source of one third of all freshwater withdrawals, supplying an estimated 36%, 42% and 27% of the water used for domestic, agricultural and industrial purposes, respectively2. In many environments, natural groundwater discharges sustain baseflow to rivers, lakes and wetlands during periods of low or no rainfall. Despite these vital contributions to human welfare and aquatic ecosystems, a paucity of studies on the relationship between climate and ground water severely restricted the ability of the Intergovernmental Panel on Climate Change (IPCC) to assess interactions between ground water and climate change in both its third3 and fourth4 assessment reports. There has since been a marked rise in published research5–8 applying localto global-scale modelling, as well as ground-based and satellite monitoring, which has considerably enhanced our understanding of interactions between ground water and climate. Here we build on an earlier broad-based overview8 of the topic, and examine substantial recent advances. These include emerging knowledge of the direct and indirect (through groundwater use) effects of climate forcing — including climate extremes — on groundwater resources, as well as feedbacks between ground water and climate, such as the contribution of groundwater depletion to global sealevel rise. Furthermore, we identify critical gaps in our understanding of the interactions between ground water and climate.