Analysis of actual evapotranspiration changes in China based on multi-source data and assessment of the contribution of driving factors using an extended Budyko framework

Quantifying actual evapotranspiration (ETa) changes and the drivers is important for both water and energy cycles. However, these issues are commonly limited by insufficient ETa observations. In view of this, we use GLEAM, GLASS, a complementary-relationship-based dataset, CRA-40, MERRA2, JRA-55, ERA5-Land, and NCEP/DOE to investigate ETa variability in China for 1982-2017. According to the average of these eight datasets, ETa increases significantly in most parts of China (p < 0.05). Then, an extended Budyko framework is used for attribution analysis of ETa trends. In addition to precipitation, potential evapotranspiration, and the landscape parameter n, the framework incorporates terrestrial water storage and external water supply. The results indicate that potential evapotranspiration positively contributes to ETa in most areas of China. The positive contribution of precipitation is mainly observed in the eastern part of northwest China and the central and eastern parts of the Tibetan Plateau. Terrestrial water storage has a positive contribution in northwest and North China. External water supply has a large contribution in northeast China, northwest China, the western Tibetan Plateau, and the Yangtze River basin, and it is closely related to the normalized difference vegetation index (NDVI). Moreover, most of the regions with high contribution of external water supply are in mountainous areas due to the regulation of topographic slope. Taking the landscape parameter n = 3.0 as a reference, the uncertainty of the extended Budyko framework is between - 30% and 25%.