Lead
Groundwater shortage due to climate change? Groundwater plays a major role for water supply in Switzerland. How does climate change affect different groundwater resources? What are the consequences for water supply?

Lay summary
Background
Approximately 80% of our drinking water comes from groundwater, which also ensures a minimal stream flow during dry periods. Groundwater is formed by precipitation and river water seeping into the underground. In future, less precipitation is to be expected during the summer, but more in the winter. In addition, some rivers will carry less meltwater during the summer due to glacier retreat.

Objectives and methods
We want to understand what effects these changes will have on different groundwater resources in Switzerland. Potential longer dry spells will be of particular interest. It is to be expected that during the dry summer months, the available water volume will diminish. As the need is highest during this period, this could lead to local water shortages. Particularly small groundwater resources could dry up quickly. Large resources however can store the precipitation which will, in future, increase during the winter. During the following dry spells, this groundwater will then feed rivers, on the one hand, and can be used as a water supply on the other. In order to better understand this relationship, climate predictions and hydrological regime models will be combined.

Significance
Groundwater is the most important source of drinking water in Switzerland. We need a sound decision-making basis and knowledge on the future effects of global change, so that the water supply can be secured on a long-term basis. This study makes it possible to identify sites with only small available water volumes, so that measures can be taken in good time.