The Grain for Green Project (Gfgp) Aggravates Evapotranspiration in the Revegetation Region in the Chinese Loess Plateau

The study of evapotranspiration (ET) is of great theoretical and practical significance for understanding the regional ecological and environmental problems and hydrological cycle processes. The Grain for Green Project (GFGP) in the Chinese Loess Plateau was used as the study area. Based on various ET data, normalized vegetation index (NDVI), gross primary productivity (GPP), soil water content (SWC), and meteorological data, we investigated the spatial and temporal variation of ET before and after GFGP by using trend analysis, stepwise regression analysis, and generalized linear model. The results showed that: (1) the Global Land Evaporation Amsterdam Model (GLEAM) data had the highest accuracy in the study area compared with other ET data; (2) the trend of ET increased significantly after GFGP, but there were large spatial differences in its variability, among which, the trend of annual precipitation varied most in the area of 400-500 mm; (3) compared with the average growing season temperature and precipitation, soil water content, NDVI and GPP were the main influencing factors of ET change in the study area; (4) the increase of ET trend after GFGP was more attributed to the acceleration of vegetation growth, and the contribution of soil water content to ET decreased, while the contribution of NDVI and GPP increased. This study provides a scientific basis for assessing the impact of the project on the hydrological processes in the region. It is suggested that when carrying out vegetation restoration work in the Loess Plateau area, priority should be given to tree species that consume less water, optimize the vegetation structure of the community, make full use of light, water, and heat resources, and build water storage facilities to support the sustainable development of the regional ecological environment