Aquifer responses to long-term climatic periodicities

Groundwater is an important resource for drinking water supply, and is subject to natural variation as well as climate change effects. It has been shown that long-term natural variations of groundwater levels can often be attributed to climatic oscillations. Long-term groundwater level records are rare, but of special importance for the detection of longer, decadal to multi-decadal periodicities, which are vital for predictions of future development of groundwater levels and the distinction between natural variation and climate change effects. We have examined periodicities of nine groundwater level time-series with records of more than 100 years, as well as possible impacts of climatic teleconnections (NAO, AMO and ENSO) with wavelet analysis. The monitoring wells are located in Germany, Netherlands, UK and Denmark and cover different depths to groundwater, different aquifer types and hydraulic conditions. Our results show that all evaluated monitoring wells exhibit significant relations to long-term climatic periodicities of NAO, AMO and ENSO. Among the wells in phreatic porous aquifers, there is a signal damping, which can be related to the thickness of the unsaturated zone. Further, the damping is higher in the lower permeable aquifers and there is less damping in the karstic aquifers compared to the porous aquifers, in spite of a much thicker unsaturated zone.