Temporal And Spatial Changes Of Vegetation Cover And Its Impact On Runoff In The Wujiang River Basin

Vegetation is one of the most fundamental components of terrestrial ecosystems,playing an indispensable role in connecting ecological factors such as atmosphere,land,and hydrology.In recent years,due to continuous climate change and intensified human activities,the growth of vegetation around the world has been affected to varying degrees,and vegetation change has also profoundly affected river runoff.This article takes the environmentally fragile Wujiang River Basin as the research object.Based on hydrological and meteorological observation data from 1982 to 2020 and normalized vegetation index(NDVI)data,statistical analysis and modeling methods are used to comprehensively analyze the spatiotemporal changes in vegetation cover and its impact on runoff in the Wujiang River Basin.The main research content and results of the paper are as follows:(1)Analysis of vegetation changes and attribution in the Wujiang River Basin.The research mainly uses the Sen+Mann Kendall method,coefficient of variation method,partial correlation coefficient,geographic detector,improved residual trend method,and Hurst index method to study the spatiotemporal changes of vegetation in the Wujiang River Basin,its correlation with climate,spatial driving factor analysis,attribution analysis,and future trends.The results show that during the period of 1982 to 2020,vegetation in the Wujiang River Basin increased by over 99.17%,with an average growth rate of 0.00337/a.97.42% of the areas showed significant improvement in vegetation,with high-speed growth mainly occurring in high-altitude areas in the southwest,and vegetation degradation occurring in about 0.83% of the areas;Mainly concentrated around the big cities of Guiyang and Zunyi.The instability of vegetation is mainly caused by the project of returning farmland to forests and the rapid expansion of urbanization.The distribution of temperature and precipitation within the watershed is uneven,with both positive and negative partial correlation coefficients with NDVI.The impact of temperature on vegetation is much greater than that of precipitation.Human activities are the dominant factor in the spatial distribution of vegetation and play a major role in spatiotemporal evolution.The relative contribution of human activities to vegetation change is about 76.98%,climate change is about 23.02%,precipitation is 6.43%,and temperature is 16.59%.90.22% of the vegetation in the area will not grow sustainably in the future.(2)Analysis of the evolution characteristics of the hydrological regime in the Wujiang River Basin.The study mainly used Mann Kendall test,wavelet analysis,hydrological change indicators(IHA),composition of environmental flow,and biodiversity index SI to comprehensively analyze the runoff changes in the Wujiang River Basin.The results indicate that during the period of 1982 to 2020,the annual runoff of the Wujiang River showed a downward trend,with a sudden change in 2004.Runoff has cycles of about 5 years,8 years,and 20 years,with the 20 year cycle being the most oscillatory and the first main cycle.After the sudden change in 2004,the comprehensive hydrological changes in the basin reached a moderate level of 47%,with the most significant decrease in flow from June to August.However,there was a slight increase in flow in January,February,April,and May,with a decrease in the frequency and duration of high pulses and an increase in the number of low pulses.Major floods no longer occur,and the frequency and range of flow changes in extreme dry seasons decreased significantly.The biodiversity index also increased.(3)Research on the impact of vegetation changes and various factors on runoff.The study used Budyko Fu hydro thermal coupling simulation and random forest model to calculate the contribution of NDVI and other factors to runoff evolution,and then combined with the impact of human activities on vegetation to calculate the contribution of ecological protection measures to runoff change.The results indicate that under the Budyko Fu hypothesis,the maximum relative contribution rate of precipitation to runoff changes is about56.93%,potential evaporation is 12.07%,and underlying surface parameters are 31%,with NDVI being 11.66%.However,in the simulated attribution of random forest,the relative contribution rate of precipitation to runoff is 53.46%,followed by potential evapotranspiration,with a contribution rate of 34.16%,and the contribution rate of NDVI to runoff is 12.38%.Through comprehensive discussion and verification,the contribution rate of NDVI to runoff is 12.02%,and the calculated contribution of ecological protection measures to runoff change is 9.17%.