Spatial patterns and seasonality of drought in Switzerland under present and future climatic conditions, and irrigation water requirements

In Switzerland, as elsewhere in Europe, recurrent drought has been one of the main concerns of the agricultural sector during the last few decades. The dry years of 2003, 2006, 2015, 2018 and again 2022 had serious impacts on forage production. As a result, additional imports were necessary to support in particular the dairy sector. Another consequence of the drought was an increase in the need for irrigation, which, however, could not always be met. Eventually, farmers had to accept restrictions on water withdrawals on several occasions. Climate change projection indicate that such situations could become more common in future.

To increase preparedness and help the agricultural sector, as a whole, better cope with drought under future climatic conditions, quantitative information on drought occurrence at regional to national scale is required. In this contribution, we present a drought assessment for Switzerland that addresses the following questions: (i) Spatial patterns of drought. What was the geography of drought events in the recent pat? Can we expect similar geographic patterns in the future? (ii) Seasonality and persistence of drought. Has there been a shift the temporal characteristics of drought because of climate warming? Are further shifts likely to occur in future? (iii) Irrigation requirements: Has the need for irrigation already increased in the recent past? If yes, where and by how much? What can be expected in this respect for the coming decades?

We base our analysis on high-resolution, gridded meteorological data and climate change projections, and use drought indices to characterize drought events in time and space. We further show how a simple model that relates irrigation requirements to a drought index can be employed to estimate current and future needs across Switzerland. Finally, we discuss how these results can be integrated in initiatives aiming at supporting farmers in the process of adaptation.