Correlating between evapotranspiration and precipitation provides insights into Xilingol grassland eco-engineering at larger scale

The Xilingol Grassland in Northern China is the largest grassland ecosystem of Inner Mongolia and plays an important role in the local ecosystem. However, grassland desertification and degradation are quite severe in this area. Therefore, we simulated the daily actual evapotranspiration (ET) and soil water content in a representative area of the Xilingol Grassland, West Ujimqin Balaguer River basin, during the grass growth period by using the dual crop coefficient model. In addition, we compared the simulation results with actual data and found that the R2 value between the actual measurement data and simulation data for soil water content was 0.662 with an error of 4.14%. The simulated total ET during the entire growth period in 2013 was 332.41 mm, including 215.13 mm grassland transpiration (64.7%) and 117.28 mm soil evaporation. Then we randomly selected precipitation and ET values for different growth periods for analysis. The results showed that the absolute R values are all higher than 0.5, which indicates that variations in ET are highly correlated with precipitation over time. By reducing the precipitation to half the actual values, the model predicts 257.71 mm ET (22.5% less than the value in natural conditions), 176.84 mm transpiration (17.8% less than the value in natural conditions), and 80.87 mm soil evaporation (31% less than the value in natural conditions). By assuming that the precipitation was reduced by half, the model predicts 274.89 mm ET (17.3% less than the actual value), 190.05 mm grassland transpiration (11.7% less than the actual value), and 84.85 mm soil evaporation (27.7% less than the actual value).