Resolution-dependence of future European soil moisture droughts

Abstract. Global climate models project an intensification of future soil moisture droughts over large parts of Europe. 
This paper investigates the impact of model resolution on the severity and seasonal cycle of future European droughts.
 We use a 6-member ensemble of the general circulation model EC-Earth to study two periods representative of the start and end of the 21st century under low-to-moderate greenhouse gas forcing (RCP4.5).
 In our study area, central-western Europe, at high spatial resolution (~ 25 km) droughts are more severe and start earlier in the season than at standard resolution (~ 112 km).
 Here, changes in the large-scale atmospheric circulationand local soil moisture feedbacks lead to enhanced evapotranspirationin spring and reduced precipitation in summer.
 A more realistic position of the storm trackat high model resolution leads to reduced biases in precipitation and temperature in the present-day climatology, which act to amplify evapotranspirationin spring.
 Furthermore, in the high resolution model a stronger anticyclonicanomaly over the British Isles extends over our study region and supports soil drying.
 The resulting drier soil induces stronger soil moisture feedbacks that amplify drought conditions in summer. 
In addition, soil moisture-limited evapotranspirationin summer promotes sensible heatingof the boundary layer, which leads to a lower relative humidity with less cloudy conditions, an increase of dry summer days, and more incoming solar radiation. As a result a series of consecutive hot and dry summers appears in the future climate. 
The enhanced drying at high spatial resolution suggests that future projections of central-western European droughts by CMIP5 models have been potentially underestimated.