Research On The Effect Of Vegetation Restoration On Runoff In Karst Watershed

The ecological environment in karst areas is fragile,and water resources have been an important factor hindering local socio-economic development and ecological construction.Large-scale vegetation restoration will have an impact on runoff while improving the ecological environment of the region.In assessing the impact of vegetation restoration on runoff in this region,a single watershed cannot tell the story,and a comprehensive assessment is needed in combination with multiple watersheds.This paper firstly analyzes the intra-and inter-annual variation characteristics of runoff and precipitation in the watershed based on mathematical and statistical methods.Second,a runoffprecipitation/temperature random forest regression model before vegetation restoration is established to simulate the runoff after the implementation of the vegetation restoration project.The contribution values of vegetation restoration and climate change to runoff changes are calculated,and the contribution rates of vegetation restoration and climate change to runoff changes are quantitatively distinguished.On this basis,the runoff characteristic values can be calculated to obtain the change of runoff characteristic values caused by vegetation restoration alone.Finally,a multi-basin comparison is conducted to comprehensively evaluate the impact of vegetation restoration on runoff.The main conclusions of this paper are as follows:(1)The runoff in each basin is unevenly distributed within the year,with runoff on a monthly scale concentrated in June and July,and on a seasonal scale concentrated in summer and autumn,with more than 70%of the runoff in each basin concentrated in the flood season.Precipitation within the basins is unevenly distributed within the year,with more than70% of the annual rainfall concentrated in April-September and the most precipitation in June.The interannual variability of annual runoff and annual precipitation in different watersheds is small.The annual average enhanced vegetation index(EVI)values in different watersheds showed a significant increase after the implementation of the ecological restoration project.(2)Annual runoff in the Libo and Songkan watersheds was mainly influenced by vegetation restoration,while the Liudongqiao,Caopingtou and Xiangyang watersheds were mainly influenced by climate change.The impact of vegetation restoration on runoff in different seasons is different in each watershed.The runoff in Libo watershed is affected by vegetation restoration in different seasons,Songkan watershed is affected by vegetation restoration in spring,autumn and winter runoff,Liudongqiao watershed is affected by vegetation restoration in spring and winter runoff,Caopingtou watershed is affected by vegetation restoration in winter runoff,and Xiangyang watershed is affected by vegetation restoration in spring and winter runoff.The impact of vegetation restoration on spring and winter runoff is greater in the Xiangyang watershed.In the Libo watershed,vegetation restoration had a greater impact on runoff in both flood and nonflood periods.In Songkan watershed,revegetation mainly affected runoff in non-flood season,and in Liudongqiao watershed,revegetation mainly affected runoff in flood season.In the Caopingtou and Xiangyang watersheds,both flood and flood runoff were less affected by vegetation restoration.(3)Except for the Songkan watershed,the vegetation restoration mainly increased the annual runoff in each watershed,but its increase decreased year by year.In terms of the increase in multi-year average runoff volume in each watershed,the increase in annual runoff volume in each watershed was not significant.In terms of the changes in monthly mean runoff due to vegetation restoration,the greatest changes in mean runoff were observed in May to July in each watershed.In different watersheds,vegetation restoration reduced the average runoff volume in different seasons in Songkan watershed,while in other watersheds,vegetation restoration mainly increased the average runoff volume in different seasons.In terms of the effect of vegetation restoration on seasonal scale average runoff,vegetation restoration mainly increased the average runoff in summer and autumn.In terms of the magnitude of the increase in mean runoff volume in different seasons,the vegetation restoration increased the mean runoff volume in summer the most.Except for the Songkan watershed,where vegetation restoration reduced the average runoff volume in both flood and non-flood seasons,the restoration of vegetation in other watersheds mainly increased the average runoff volume in both flood and non-flood seasons.(4)Except for the Songkan watershed,the restoration of vegetation in the other watersheds mainly increased the annual runoff coefficient.In terms of the magnitude of increase in multi-year average runoff coefficients,the increase was small in all of them.Vegetation restoration mainly increased the annual runoff coefficient of variation in each watershed.In terms of the magnitude of the increase in the annual runoff coefficient of variation due to vegetation restoration,the largest increase was observed in the Xiangyang watershed and the smallest increase was observed in the Libo watershed.From the trend of annual mean runoff variability caused by vegetation restoration,the mean runoff variability caused by vegetation restoration generally showed a decreasing trend,and the impact of vegetation restoration on runoff decreased year by year.