Evapotranspiration trend detection in Austria: A comparison of global remote sensing and reanalysis products with water-balance estimates

Study region The study investigates 130 watersheds across Austria spanning four major hydro-climatic regions to assess long-term changes in evapotranspiration (ET). Study focus Previous studies have reported increasing water-balance ET across Austrian catchments during recent decades; however, it remains unclear whether widely used global ET products can reproduce these trends. This study evaluates whether five remote-sensing and reanalysis ET datasets (ERA5, MERRA-2, GLEAM, GLDAS, and MODIS) reproduce water-balance ET trends for two periods: 1981–2020 and 2001–2020. New hydrological insights for the region Water-balance ET (ET WB ) increased in Austria over 1981–2020 (field-mean slope +14 mm yr⁻¹ decade⁻¹, 95% interval +3 to +26); 37 of 130 catchments showed significant trends, 34 of them increasing. In 20-year windows ending after 2010, the median slope turned negative, from +45 (1981–2000) to −15 mm yr⁻¹ decade⁻¹ (2001–2020). This decline is indicative only: the 2001–2020 field-mean slope of −18 mm yr⁻¹ decade⁻¹ has an interval reaching zero (−38 to +2), and the six significant trends equal what chance would give (6.5 of 130). The global ET products do not follow the decline: ERA5 and GLEAM keep positive median slopes in all windows, MERRA-2 only drops to about zero, and product slopes correlate weakly with ET WB slopes (|r| ≤ 0.26). Global ET products should therefore be used with caution when assessing ET trends in Central European catchments.