| Vegetation plays an important role in the process of material circulation and energy flow in terrestrial ecosystems.At the same time,with the increasingly serious problems of global environmental change and global warming,surface vegetation coverage has become an important indicator of regional ecological environment health.Source area is located in the hinterland of qinghai-tibet plateau,is the birthplace of the Yangtze river,Yellow River and lancang river,have important function of water storage and conservation,as a result,the source area of spatial and temporal variation characteristics of vegetation cover and its driving factors,to protect the ecosystem stability of source area is of great significance,also provide effective scientific basis for vegetation protection.Based on MODIS NDVI data from 2000 to 2019,the integrated use of the maximum synthetic method and monadic linear regression,spatial trend analysis,methods of variation coefficient,the area of three rivers the space-time evolution of vegetation was studied,in time and space distribution of vegetation characteristics on the basis of introducing the geographical detector and geographically weighted regression model,The driving mechanism of influencing factors of vegetation cover change was discussed.The main conclusions are as follows:(1)On the interannual scale,NDVI in the Three-River Headwaters region showed a trend of fluctuation,with a slope of 0.014/10 a.In terms of spatial distribution pattern,the mean VALUE of NDVI in the three-River headwaters region is between-0.04 and0.91 in the past 20 years,showing the overall distribution characteristics of "lower in the northwest and higher in the southeast".The areas with NDVI>0.5 account for 49.64%of the total area.In general,the areas with high NDVI values are mainly concentrated in most areas of the Source of lancang River and Yellow River.The low values are concentrated in the northwest of the source of the Yangtze River.(2)In terms of spatial variation trend,NDVI in most areas of the Three-River Headwaters region has been improved.The area percentage of obvious improvement is 22.81%,and the area proportion of slight improvement is 42.85%.The improvement effect is more obvious in the northeast of the Yellow River headwaters basin and the northwest of the Yangtze River Headwaters Basin,and the area of obvious degradation is less.However,in terms of dynamic persistence,the areas with uncertain future NDVI trends account for more than 70%,and the areas with obvious continuous improvement only account for 6.19%of the total area.Most of them are distributed in the northeast of the Source of the Yellow River,which needs to be paid attention to.In terms of spatial stability,it is mainly manifested by the co-existence of high and low fluctuation regions and the high proportion of low fluctuation regions.(3)It can be seen from the results of geographical detector that climate factors are the main factors affecting the spatial differentiation of NDVI,and the explanatory power level fluctuates.Precipitation,temperature and light duration are always the dominant factors in the detection.The interaction between different driving factors was greater than that of single factor detection,with two-factor enhancement as the main factor,and a small part of interaction type was nonlinear coordination enhancement,indicating that the process of spatial differentiation of vegetation cover in the Threeriver Headwaters region was the result of interaction between multiple factors.Risk detection showed that NDVI and precipitation present obvious positive correlation,while with sunshine duration and wind velocity was significantly negative correlation function of the temperature,relative humidity and evaporation capacity are in the seventh division of the highest average NDVI and vegetation growth well geomorphic types and soil types of ups and downs in the mountain and felt of black soil,respectively,When the sand and clay contents were 45.4%～49.8% and 22.9%～26.9%,the vegetation growth was better.(4)Combined with the geographical weighted regression model,the spatial visualization analysis of the regression coefficients of NDVI impact factors was carried out to explore the effects of different impact factors on vegetation coverage in the Three-River Headwaters region and its spatial heterogeneity.The results showed that there were significant differences in the influencing factors and degree of spatial change of vegetation cover.The effects of precipitation,air temperature and clay content on vegetation cover were mostly positive,while the effects of wind speed and sand content on vegetation cover were mostly negative.Among them,NDVI is significantly affected by precipitation and clay content in the northeastern part of the study area and the central and northern part of the Source of the Yangtze River,and is significantly affected by air temperature and sand content in the southeast and central and southern parts of the study area with abundant precipitation,while in the northwest part of the Source of the Yellow River,wind speed has a significant impact on vegetation coverage. |
