Response Of Runoff To Forest Cover Change In Jiuzhaigou Based On SWAT Model

In recent years,the relationship between forests and water has been the focus and difficulty in studying the problems related to forest ecological balance.Therefore,it is important to study the past hydrological processes to grasp the rules for future forest protection.In this paper,taking Jiuzhaigou National Nature Reserve as an example,the model was constructed using DEM digital elevation model data,forest cover data in 2004 and 2016,soil type distribution data,CMADS meteorological dataset,and runoff data.The impact of forest cover change on runoff was studied by simulating the forest cover in 2004 and 2016,and the spatial distribution of water production was analyzed based on the response of monthly average runoff during abundant,flat and dry periods under forest cover change.In addition,remote sensing data were used to decode the dynamic changes of water area of the study lakes in Jiuzhaigou watershed,and then the relationship between water area and measured runoff was fitted by SPSS to quantify the changes of water area of typical lakes under forest vegetation cover.The purpose of this paper is to quantify the effect of forest cover change on the watershed runoff and the effect of forest cover change on the watershed area of the study lakes in order to protect the core values of the Jiuzhaigou watershed and to evaluate the most worthwhile seasons for tourists.This study shows:(1)The SWAT model shows some applicability in Jiuzhaigou watershed.Although there is a certain gap between the simulated peak and valley times and the actual situation,it is consistent with the actual situation in terms of the time of peak and valley occurrence.And the Nash efficiency coefficients(Ens)and coefficients of determination(R2)of the model rate period and validation period meet the requirements of model accuracy.(2)The most dominant vegetation cover types in Jiuzhaigou watershed are coniferous forests dominated by fir and spruce forests and broadleaf forests dominated by oak and birch forests.between 2004 and 2016,under the effect of natural forest succession,the overall forest cover area showed an increasing trend,and the overall forest area of coniferous forests increased,with the increase accounting for about 1.63% of the entire watershed area,while the area of broadleaf forest type woodland The area of broadleaf forest decreased by 0.41%.(3)From the change of the average annual runoff volume,the average annual runoff volume under the forest cover in 2016 is 0.13 m3/s larger than that in 2004.except for 2012 and 2013,in years with abundant precipitation,the annual runoff volume in 2004 is smaller than that under the forest cover in 2016;while in years with less precipitation,the annual runoff volume in 2004 is larger than that under the forest cover in 2016.The annual runoff in 2004 was greater than the annual runoff under forest cover in 2016.In terms of monthly runoff,the overall change in runoff under forest cover in 2004 and 2016 tends to be the same.The monthly runoff under the forest cover in 2016 was smaller than that in 2004 during the high water period,while during the low water period,the monthly runoff under the forest cover in 2016 was larger than that in 2004,indicating that coniferous forests had better water holding capacity during the high water period and stronger water production capacity during the low water period than broadleaf forests during the intra-annual variation.(4)The change in interannual water area in Jiuzhaigou over the past 9 years has been positive,with an overall gradual stabilization and a slight upward trend,indicating that the increase in coniferous forest is beneficial to forest water production,and the stability of interannual water area change in the water landscape will be further maintained in the future with the development of forest restoration succession.The intra-annual variation trend of water area showed a bimodal distribution under forest vegetation cover in both 2004 and 2016,and the lowest value occurred in March under forest cover in both periods,the former showed a significant highest value around July,and the latter could extend the viewing time in October-December in the scenic area.Using the fitted relational equation to quantify the water area in different seasons,it can be seen that the performance of the water landscape viewing period is autumn > summer > winter > spring.