Evaluation of the value of water retention service in the middle and upper reaches of Hunhe River based on SWAT Model.

The upper and middle reaches of the Hunhe River, with forest coverage rate up to 68%, is an important water source protection area in Liaoning Province. Based on the SWAT model and shadow engineering method, we aimed to estimate the function and service value of water retention in the upper and middle Hunhe River basin from 2000 to 2019, to analyze the spatial heterogeneity, and to provide a scientific basis for the ecological compensation and ecological restoration of the region. Our results showed that the function and service value of water retention in the upper and middle reaches of the Hunhe increased first, and then decreased from 2000 to 2019. The mean annual amount and service value of water retention were 2.46 billion m and 15.04 billion yuan, respectively. The spatial distribution of water conservation service functions in the study area was uneven. The areas of high water retention service value were mainly distributed in Qingyuan County and Xinbin County, while the low-value areas were located in municipal districts of Shenyang City. The value of water retention services was obviously different among the ecosystems, with water retention capacity per unit area of forests being much higher than that of grassland, farmland, and cities.