Spatiotemporal variation characteristics of actual evapotranspiration based on remote sensing and flux observations: case study in the water conservation area of the Yellow River basin

Evapotranspiration (ET) is an important component in the surface water-heat balance, and accurate analysis of the spatiotemporal distribution characteristics of evapotranspiration and its influencing factors is crucial for understanding the hydrological cycle and ecosystem of specific regions. Based on flux observatory data from the Yellow River basin water conservation area, we evaluated the applicability of four ET products, Global Land Evaporation Amsterdam Model (GLEAM), Model Tree Ensembles (MTE), Global Land Data Assimilation System (GLDAS), and Advanced Very High Resolution Radiometer (AVHRR), and applied the water balance principle to verify their accuracy at the basin scale, and to discuss the influencing factors of actual ET. Results showed that the GLEAM ET product had the highest accuracy at site scale. At basin scale, the relative errors of ETGLEAM and ETP-R were the smallest in a tributary basin of the Weihe River in the southern mountains, followed by the basin above Lanzhou. Actual ET in the water conservation area of the Yellow River basin showed an overall increasing trend during 1982—2015, and a gradual increase from the west toward the east in terms of spatial distribution. The annual average ET varied greatly among different vegetation types, with broadleaved forests showing the largest ET (575.2 mm), followed by farmland (504.3 mm), and alpine meadows showing the smallest ET (358.2 mm). Actual ET is mainly affected by solar radiation and temperature.