Research on regional evapotranspiration in the Zhangcheng area based on the SEBS model

Evapotranspiration (ET) is the main process of water and energy conversion in the hydrosphere, atmosphere and biosphere. Accurately estimation of ET is of great significance in ecological environment protection. The city of Chengde and Zhangjiakou, taken as the study area, is an important barrier for the ecological security of the Beijing-Tianjin-Hebei urban areas. There have been fewer studies of actual evapotranspiration for long-term sequences in the region. In this paper, the monthly actual ET in the study area from January, 2001 to December, 2020 is simulated based on the SEBS model using MODIS and GLDAS data. The SEBS results are compared with the MOD16A2 data in trend, and the field measurements on July 2021 are also used for validation at the pixel scale. The method of Sen+MannKendall test is used to analyze the temporal and spatial trend changes, and the correlation analysis was used to discuss the influencing factors on ET change. The results show that the monthly SEBS ET has a good correlation with the mod16A2 data, and the relative error with the field measurement is less than 15%. Therefore, the reliability of the SEBS result is validated to be relatively high. The actual ET of the study area has shown a fluctuating upward trend in the past 20 years. The maximum value of ET appeared in 2013 with the value of 545 mm, and the minimum value was 348 mm in 2002; and the evapotranspiration in Chengde was significantly higher than that in Zhangjiakou; In the past 20 years, the ET of 75.41% of the study area was basically stable, 5.13% of the area increased, 1.11% of the region was significantly decreased and 18.35% of the area was slightly decreased. The temperature and vegetation change have a significant positive correlation with evapotranspiration variation. The ET of different land use types is: forest land>water>grass land>arable land>construction land>unused land.