Estimation and spatio-temporal characteristics of winter wheat evapotranspiration in Henan Province based on NPP VIIRS data and SEBS model

Crop evapotranspiration (ET), a key variable in water and heat exchange in agricultural fields, is of great significance for understanding the dynamics of soil moisture changes in agricultural fields, monitoring and predicting crop drought conditions, and guiding scientific irrigation. This study combined the surface energy balance system (SEBS) model to estimate ET of winter wheat in Henan Province during the critical growth period from 2016 to 2018 using the visible infrared imaging radiation suite (VIIRS) data of the Suomi National Polar-orbiting Partnership (NPP) satellite. Experimental accuracies were compared between VIIRS ET and the other three ET products (estimated by Penman-Monteith formula, P-M ET; estimated with MODIS data, MODIS ET; and macro-weighing lysimeter-measured ET, Real ET), and the spatial and temporal variation characteristics of ET in winter wheat area of Henan Province were analyzed. The results showed that comparing the VIIRS ET estimated by our proposed method with the P-M ET, the total average relative deviation was 10.1%, and VIIRS ET exhibited high consistency with P-M ET. The measured ET of the macro-weighing lysimeter was used to verify accuracy, and the root mean square error (RMSE) of the calculated VIIRS ET was 0.203 mm·d^–1. The verification results showed that the NPP VIIRS data are suitable for ET inversion. The determination coefficients of linear regression analysis of VIIRS ET and MODIS ET were 0.804, 0.734, and 0.802 for the April 17^th in 2016, 2017 and 2018, respectively. The three years RMSE of VIIRS ET based on MODIS ET were 0.222 mm·d^–1, 0.158 mm·d^–1, and 0.211 mm·d^–1, respectively. This shows that there is good consistency between VIIRS ET and MODIS ET, and that VIIRS data can be used as an effective supplement and substitute. The ET spatial distribution was generally higher in the middle and southeast and gradually decreased to the northwest and southwest. The spatial variation characteristics of ET corresponded well with that of irrigation conditions. According to the time characteristics of farmland ET during the key growth period of winter wheat in the study area, the average daily ET in the regeneration stage was the lowest, and then it increased gradually, reached a maximum at the heading stage, and began to decrease at the filling stage. The temporal and spatial characteristics of winter wheat field ET in Henan Province were closely related to the local field management mode. The accurate estimation of winter wheat field ET can provide a scientific basis for the design of irrigation management systems. This is important for the management, distribution, and efficient utilization of agricultural water resources.