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

Traditional air temperature-based climate heat indices can be of high uncertainty in regions where ground observations are scarce. In this study, we calculate the Summer Days and Tropical Nights heat 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 from EUMETSAT’s Satellite Application Facility on Climate Monitoring (CM SAF). We define relative indices that account for the intermittency of clear-sky LST satellite observations. Furthermore, we propose a novel “Extremely Hot Days index”, tailored to satellite LST data. We find that these LST-based indices are highly correlated with station-based air temperature indices in Switzerland, with coefficients of determination R2 of 0.86, 0.84, and 0.81. Results show a strong increase in LST-based heat indices of up to 12 days/decade since 1991 in parts of Europe, including the Po Valley and the Mediterranean coast. These new LST heat indices can capture changes in heatwave patterns and trends for clear-sky conditions in Europe with unprecedented spatial resolution. They complement traditional air temperature heat indices and enable future climate change studies, also in regions with sparse ground observations.