Regime shift in groundwater temperature triggered by the Arctic Oscillation

[1] Groundwater is the world's most important source of raw drinking water. However, the potential impact of climate change on this vital resource is unclear because of a lack of relevant long-term data. Here we statistically analyze over 20 years of groundwater temperature data from five Swiss aquifers fed predominantly by river-bank infiltration. The results reveal an abrupt increase in annual mean groundwater temperature centered on 1987–1988 that can also be observed in air and river temperatures. We associate this temperature increase with the Northern Hemisphere late 1980s climate regime shift (CRS), which itself is related to an abrupt change in the behavior of the Arctic Oscillation. Because temperature affects redox conditions in groundwater, groundwater biogeochemistry in aquifers fed by river-bank infiltration is likely to depend on large-scale climatic forcing and will be affected by climate change.