Contribution of climate change and vegetation restoration to interannual variability of evapotranspiration in the agro-pastoral ecotone in northern China

Evapotranspiration (ET) is a vital variable in the water and energy cycles and significantly influenced by changing environmental conditions. However, in the data-lacking agro-pastoral ecotone in northern China (APENC) that has undergone warming and wetting climate trend and implemented a series of ecological restoration projects (ERP), the effects of climate change and vegetation greening on the magnitude, drivers, and mechanism of ET variations are not fully understood yet. In this study, we evaluated nine commonly used ET products to determine the most applicable one in the APENC based on the in-situ observations and water balance method. Subsequently, the ET variation was examined and the contribution of each factor to the ET change from 1982 to 2017 was quantified. Results show that the Global Land Evaporation Amsterdam Model (GLEAM) performed best and meets the accuracy requirements for research in the APENC. Based on the GLEAM data, our analysis reveals a notable increase in ET at a rate of 1.11 mm/y (p < 0.05). Regions with a significant increase in ET are mainly concentrated in the middle and southwest parts of the APENC, while a decreasing trend in ET is observed in the northeast region. Contributory analysis showed that precipitation (PRE) and leaf area index (LAI) were the dominant factors that controlled the ET variation, whereas air temperature indirectly affected ET variation by promoting LAI growth during 1982-2017. PRE dominated the variation of ET before the implementation of ERP (1982-1999), while the positive contribution of LAI exceeded PRE since 2000 to become the dominant factor. Our findings bridge the gap in ET research in the study region and provide important information for water resource management and ecological rehabilitation.