Global warming of groundwater due to climate change

Aquifers contain the largest reserves of unfrozen freshwater, making groundwater critical for life on Earth. Surprisingly little is known about how groundwater responds to surface warming at spatial and temporal scales. We focus on diffusive heat transfer, simulating current and predicted groundwater temperatures on a global scale. We show that groundwater at depth to the water table (excluding permafrost regions) is conservatively projected to warm by 2.1°C on average between 2000 and 2100 under the medium emissions pathway. However, regional patterns of shallow groundwater warming vary widely due to the spatial variability of climate change and water table depth. The lowest rates are predicted in mountainous regions such as the Andes or the Rockies. We illustrate that increasing groundwater temperature affects flow thermal regimes, groundwater-dependent ecosystems, aquatic biogeochemical processes, groundwater quality, and geothermal potential. The results suggest that by 2100 under the medium emissions path, an estimated 77 million to 188 million people will live in areas where groundwater exceeds the highest drinking water temperature limit set by any country. (Susanne A. Benz, Dylan J. Irvine, Barret L. Kurylyk, more at nature.com)