Heat Indices for Europe Derived From Satellite Data: A Proof of Concept

Traditional air temperature-based climate indices can be of high uncertainty in regions where ground observations are scarce. In this study we demonstrate how satellite-based heat indices can overcome the lack of station data. We calculate Summer Days and Tropical Nights indices defined by the Expert Team on Climate Change Detection and Indices (ETCCDI) for Switzerland and Europe, based on long-term Land Surface Temperature (LST) satellite climate data being available through EUMETSATs Satellite Application Facility on Climate Monitoring (CM SAF). Furthermore, we developed a novel "Extremely Hot Days index", particularly tailored to satellite-based LST data. We find that these satellite-based indices are highly correlated with station-based indices in Switzerland with coefficients of determination R2 of 0.86, 0.84 and 0.81. Results show strong increase in the satellite-based climate indices of up to 12 days per decade since 1991 in parts of Europe such as the Po Valley. With the new Extremely Hot Days index we find a pronounced increase of up to 12 days per decade along the Mediterranean coast, complementary to traditional indices. This demonstrates that satellite-based LST has a high value for accurately monitoring heatwaves. The presented methods can be applied globally wherever stable satellite data is available.