Temporal and spatial distribution characteristics of evapotranspiration in the Huang-Huai-Hai River basin

Evapotranspiration is a key element connecting the energy cycle and water cycle of the climate system. It is of great significance to explore the evolution of actual evapotranspiration and its influencing factors in the Huang-Huai-Hai (HHH) River basin, which helps to understand the response of the regional water cycle to climate change. To this end, the GLEAM actual evapotranspiration (ET) dataset over the HHH River basin from 1980 to 2018 was collected, together with the parallel Normalized Difference Vegetation Index (NDVI) data and station-based meteorological observations (precipitation and air temperature). The linear regression method, Mann-Kendall trend test and correlation analysis methods were used to analyze the variations of ET and its influencing factors in the research area of interest. The results show that: the accuracy of the verification results between the GLEAM products and the reference value in the HHH River basin was better, and the mean annual ET of the HHH River basin was 474 mm, showing a significant upward trend. In terms of the spatial heterogeneity, the mean annual ET ranged from 183 mm to 708 mm, decreasing from southeast to northwest over the HHH River basin, which had a significant difference in spatial patterns. The spatial distribution of ET in each season with significant differences was basically similar to that of ET at annual scale. Actual evapotranspiration value and NDVI value had a significantly positive correlation, but the former had a mainly positive correlation with precipitation and temperature. The precipitation in the HHH River basin showed an insignificant increase trend, while the temperature showed a significant increase trend. The increase in NDVI was the main reason for the significant increase in actual evapotranspiration in the HHH River basin from 1980—2018.