People fetching water from a well in Kerala, South India | Photo: Till Oehler, ZMT

The Impact of Climate Change on Groundwater – a Ticking Time Bomb

According to a study recently published in the journal Nature Climate Change, in most regions of the world the effects of today’s climate changes on groundwater will only become manifest over the next 100 years, thus impacting the lives of generations that come after us.

Climate change and its immediate, already perceptible consequences, such as the melting of the polar ice caps or coral bleaching, are regularly the focus of public attention. Less attention has so far been paid to a risk hidden deep in the ground. Groundwater is also affected by climate change.

An international research team, including scientists of the Leibniz Centre for Tropical Marine Research (ZMT), has now determined how quickly groundwater reacts to climatic changes. The results of the study were recently published in Nature Climate Change.

Groundwater feeds mainly from rain that seeps into the soil and is stored there. Slowly, often only at a speed of a few metres per year, the water then flows into streams, rivers, lakes or directly into the sea. There are several factors influencing the properties of such a groundwater system: the composition of the land surface, for example, or the slope of the terrain. These determine how fast the water is exchanged.

The scientists involved in the study from Europe, North America and Australia compiled global data sets on the characteristics of groundwater systems. Using simulation models, they calculated the response times of the systems to an increased or reduced water supply, as expected in the context of climate change.

The result was that in many areas the impact of climate change on groundwater will only become noticeable 100 or more years from now. Depending on its composition, a groundwater system can buffer fluctuations in the water supply to varying degrees. In dry regions, the time span is particularly long. There, the groundwater level is usually deep in the earth, the exchange with the land surface is low.

"The problem lies in the long reaction time of the groundwater systems,” said ZMT geoscientist Nils Moosdorf, one of the authors of the study. "Groundwater systems have a 'memory' that can turn out to be an ecological time bomb. What happens to them today casts its shadow far into the future and affects the living conditions of our great-grandchildren.”

Groundwater is the largest fresh water reserve on earth. More than two billion people obtain their drinking water from groundwater. Climate change, overexploitation and the growing world population pose major challenges to the sustainable management of water resources, especially in coastal regions. The results of the study are of great importance for corresponding management plans.

Publication

Cuthbert, M.O., Gleeson, T., Moosdorf, N., Befus, K.M., Schneider, A., Hartmann, J., Lehner, B., 2019. Global patterns and dynamics of climate-groundwater interactions. Nature Climate Change, doi: http://dx.doi.org/10.1038/s41558-018-0386-4.