Detection and attribution of reference evapotranspiration change (1951–2020) in the Upper Yangtze River Basin of China

Reference evapotranspiration (ET0) indicates atmospheric evaporating capability over a hypothetical reference surface. ET0 is an important hydrological and meteorological variable to reflect climate change. This is particularly true for the Upper Yangtze River Basin (UYRB), which is vulnerable and sensitive to changing environment. This study aims to provide a newer and longer description of ET0 change and the causes at basin and subbasin scales in the UYRB. Based on the observed data from 1951 to 2020, ET0 in the entire UYRB and subbasins is estimated using the Penman–Montieth method with local calibration. The spatial–temporal characteristics in ET0 change are identified from time-series analysis. Our results show that ET0 increases significantly by 3.3 mm/year in the entire UYRB. Stations with significant increases in annual ET0 are concentrated in the central part of the UYRB, where the mean annual ET0 is low. We further propose an improved method to assess the causes of ET0 change. Our results suggest that the relative humidity decrease has the most dominant effect, causing 4.69 mm/year of ET0 increase. Temperature increase tends to cause 1.26 mm/year of ET0 increase. Sunshine duration decrease and wind speed decrease contribute to 1.96 and 0.48 mm/year of ET0 decrease.