Agricultural drought in the Alpine region – What is the role of evapotranspiration in the context of climate change?

Evapotranspiration links the earth's water and energy budgets. It also connects macro- and microclimate, as atmospheric evaporation requirements often reflect conditions at the large scale, but the rate at which the surface releases water vapor into the atmosphere is ultimately determined by processes at the local scale. In an agricultural context, evapotranspiration determines crop water requirements and is a key factor in relation to the initiation and development of agricultural drought. It has been shown in the past that in temperate climates drought occurrence and the severity of extreme drought events are sensitive with respect to the maximum evapotranspiration rates permitted by the prevailing environmental conditions. Understanding this sensitivity, and how it may evolve in the future in response to changes in the precipitation (rate of storm arrivals and mean storm depth), thermal and radiative regimes, is of fundamental importance for assessing the impacts of climate change on agricultural production.

The aim of this contribution is to provide a brief overview of the relevant concepts and the current state of knowledge, to assess whether historical variations in evapotranspiration (in relation to variations in temperature, solar radiation and atmospheric CO₂ concentrations) have influenced the occurrence of drought in the Alpine region, and to present a preliminary assessment of future changes in evapotranspiration and their implications for extreme drought events with high impact on agricultural systems, based on a new set of regional climate change scenarios for Switzerland. Results of simulations with ecosystem and ecohydrological models will be use to illustrate the main points of discussion. The issue of the need to take microclimatic constraints into account will be addressed.