Effects of Aerosol on Reference Crop Evapotranspiration: A Case Study in Henan Province, China

An increase in atmospheric pollution markedly affects the climatic environment. Aerosol is the main component of atmospheric pollutants and has a significant influence on the changes of reference crop evapotranspiration (ET0), while the effects of aerosol on ET0 are still unclear. In this study, the influence of aerosol on the changes in meteorological elements and ET0 in Henan Province was evaluated using online two-way coupling of WRF (Weather Research Forecast)–Chem. The results of the 30-day Online Two-way Coupling indicated that the WRF–Chem model accurately simulated the temporal and spatial variation of each meteorological element in Henan Province. Aerosol decreased the overall temperature in Henan Province by 0.036 °C, wind speed by 0.176 m s−1, and barometric pressure by 20 Pa, while the relative humidity increased by 1.39%. The effect of aerosol on meteorological elements led to the change in ET0. The extent of the effect of aerosol on ET0 was closely related to the aerosol concentration. The variation of ET0 ranged from −0.545 to 0.676 mm d−1 for a pollution condition and −0.309 to 0.380 mm d−1 for an excellent condition. The extent of the effect of aerosol on ET0 varied among regions, and the variation of ET0 showed distinct spatial patterns under different pollution levels. The varying degree of ET0 in the daytime (ET0-d) was greater than ET0-n (ET0 in the nighttime) regardless of the circumstances. Shortwave aerosol radiative forcing was the main cause of this phenomenon. For an excellent condition, aerosol showed positive regulation of ET0-d in 63% of the regions and of ET0-n in 88% of the regions. ET0-A (aerodynamic term of ET0) plays a dominant role in ET0 changes in most of Henan Province. However, as the pollution level increased, more urban ET0-R (radiation term of ET0) also began to dominate the ET0 changes. These results contribute to an in-depth understanding of the response of regional evapotranspiration to atmospheric pollutants and climate change.