Quantifying impacts of the drought 2018 on European ecosystems in comparison to 2003

Abstract

In recent decades, an increasing persistence of atmospheric circulation patterns has been observed. In the course of the associated long-lasting anticyclonic summer circulations, heat waves and drought spells often coincide, leading to so-called hotter droughts. Previous hotter droughts caused a decrease in agricultural yields and increase in tree mortality, and thus, had a remarkable effect on carbon budgets and negative economic impacts. Consequently, a quantification of ecosystem responses to hotter droughts and a better understanding of the underlying mechanisms is crucial. In this context, the European hotter drought of the year 2018 may be considered as a key event. As a first step towards the quantification of its causes and consequences, we here assess anomalies of atmospheric circulation patterns, temperature loads, and climatic water balance as potential drivers of ecosystem responses as quantified by remote sensing using the MODIS vegetation indices NDVI and EVI. To place the drought of 2018 within a climatological context, we compare its climatic features and ecosystem response with the extreme hot drought of 2003. Our results indicated 2018 to be characterized by a climatic dipole, featuring extremely hot and dry weather conditions north of the Alps but comparably cool and moist conditions across large parts of the Mediterranean. Analyzing ecosystem response of five dominant land-cover classes, we found significant positive effects of April-July climatic water balance on ecosystem productivity. Negative drought impacts appeared to affect a larger area in 2018 compared to 2003. We found a significantly higher sensitivity of pastures and arable land to climatic water balance compared to forests in both years. This study quantifies the drought of 2018 as a yet unprecedented event and provides valuable insights into the heterogeneous drought responses of European ecosystems.