The spatial and temporal evolution of the actual evapotranspiration based on the remote sensing method in the Loess Plateau.

Due to the joint impact of climate change and human activities, vegetation cover area in Loess Plateau has been tremendously improved. However, vegetation restoration will lead to high water use, which might pose a great threat to the water sustainability of regional ecosystems. In order to analyze the spatiotemporal characteristics of water consumption, this study estimated the actual evapotranspiration (AET) based on the SEBAL model. The study found that precipitation and AET increased significantly (5% confidence level) with the rising of vegetation coverage in the period of 1990-2015. The increase rate of precipitation was 1.91 mm/a, higher than that of AET (1.68 mm/a). From a spatial perspective, the AET of Loess Plateau is increasing from northwest to southeast. The high-AET area (AET > 400 mm) was also extremely enlarged from 39% (1990) to 73% (2015) with the vegetation recovery. In terms of the intra-annual variability, the AET from March to April is usually much higher than the precipitation in different hydrological years, which suggests that the spring drought is a potential threat for vegetation growth in Loess Plateau. At last, this study introduced an index of rainwater utilization potential indicator (IRUP) to analyze the water supply and demand in Loess Plateau. It found that IRUP values are positively correlated with NDVI (Normalized Difference Vegetation Index), indicating that the available water for vegetation growth is seemingly increasing with the vegetation cover area enlarged in the whole region.