Changes of the aridity index in Europe from 1950 to 2019

The aridity index, also known as the Budyko index, describes spatiotemporal changes in the hydroclimatic system in the long-term perspective. Defined as the ratio between potential evapotranspiration and precipitation, it can be used to determine wet (humid) and dry (arid) regions. In this study, we evaluated the aridity index estimated in different temporal scales, investigated its spatial patterns, and highlighted the long-term changes in Europe using three gridded data sets (CRU, E–OBS, and ERA5). A significant dry region expansion is evident in all data sets since the late 1980s. The extent of the dry regions has increased in Western, Central, and Eastern Europe, especially at low and medium altitudes. The results show the long-term development of the European hydroclimatic system and which areas have changed from wet to dry.