The European 2015 drought from a climatological perspective
Abstract. The summer drought of 2015 affected a large portion of continental Europe and was one of the most severe droughts in the region since summer 2003. The summer was characterized by exceptionally high temperatures in many parts of central and eastern Europe, with daily maximum temperatures 2 °C warmer than the seasonal mean (1971–2000) over most of western Europe, and more than 3 °C warmer in the east. High evapotranspiration rates combined with a lack of precipitation affected the soil moisture content and vegetation stress and led to record low river flows in several major European rivers. This paper analyses the European summer drought of 2015 from a climatological perspective, including its origin, spatial and temporal development, and how it compares with the 2003 event. It discusses the main contributing factors controlling the occurrence and persistence of the event: temperature and precipitation anomalies, blocking episodes and sea surface temperatures (SST). Central Europe experienced during the summer of 2015 widespread areas of negative Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI) values, present from May onwards. Similar to the summer drought of 2003, the upper level atmospheric circulation over Europe was characterized by a positive 500 hPa geopotential height anomalies flanked by a large negative anomaly to the north and west (i.e. over the central North Atlantic Ocean extending to northern Fennoscandia) and another center of positive geopotential height anomalies over Greenland and northern Canada. Simultaneously, the summer SST was characterized by large negative anomalies in the central North Atlantic Ocean and large positive anomalies in the Mediterranean basin. The SST dipole-like anomalies between the central Atlantic and the Mediterranean Sea suggest a possible "atmospheric teleconnection" between the two regions, which in turn may affect the drought conditions over Europe. In an accompanying paper, the hydrological perspective of the summer 2015 drought is presented. Together, these two papers summarize a collaborative initiative of members of UNESCO’s FRIEND-Water program to perform a timely Pan-European assessment of the 2015 summer drought.