| Global environmental change are rapidly changing the dynamic of terrestrial vegetation,vegetation greening in high latitudes and the Tibetan plateau is more caused by climate change.The Qinghai Lake Basin is an important ecological area of the Qinghai-Tibet Plateau and even the world.To explore the characteristics and driving forces of vegetation greening in the Qinghai Lake Basin,it can provide scientific basis for the local government to formulate ecological protection policies and productivity development mechanisms.In view of the fact that the change of natural surface vegetation green degree is closely related to the normalized difference vegetation index(NDVI)and the vegetation leaf area index,this paper takes the Modis normalized difference vegetation index(MOD13Q1-NDVI)as the index of surface vegetation green degree,combined with meteorological data,soil moisture,topography,vegetation types,land use,human disturbance,population density and other data during the same period,The spatial-temporal variability of surface vegetation in the Qinghai Lake Basin and the explanatory power and driving mechanism of different factors on the spatial-temporal variability of surface vegetation were Regression analysis by using monadic analysis,Theil-Sen Median trend analysis,Mann-kendall test,correlation analysis,and geographic detector model.The main findings are presented as follows:(1)The multi-year mean values of NDVI in spring,summer and autumn in Qinghai Lake Basin from 2000 to 2020 were 0.28,0.53 and 0.3,respectively,that is,summer>autumn>spring.From 2000 to 2020,the surface vegetation greenness(NDVI)in the Qinghai Lake Basin showed a fluctuating and upward trend in spring,summer,autumn and interannual(growing season).The change rates were 0.033/10a in spring,0.030/10a in summer,0.017/10a in autumn and 0.029/10a in interannual(growing season).The spatial distribution shows an upward trend from northwest to southeast,with obvious spatial heterogeneity.From 2000 to 2020,the multi-year mean values of surface vegetation greenness(NDVI)of different land use types were in the order of forest land>cultivated land>grassland>urban and rural areas>unused land.Among them,the forest land,grassland,cultivated land and unused land vegetation greenness(NDVI)all showed an upward trend,and the change rates were0.032/10a,0.098/10a,0.124/10a and 0.015/10a,respectively,while urban and rural surface vegetation greenness(NDVI)showed a downward trend,and the change rate was-0.11/10a.(2)The spatial distribution of temperature,precipitation and soil moisture in Qinghai Lake Basin from 2000 to 2020 has certain differences.The temperature is mainly low in the northwest and high in the Qinghai Lake area,while the precipitation shows a distribution patten of low in northwest and high in southeast,the soil moisture is generally high in the northwest and low in the surrounding area of Qinghai Lake.The change rates of temperature,precipitation and soil moisture(0-10 cm)in2000-2020 were-0.084/10a,28.61/10a and 0.009/10a,respectively.Precipitation and soil moisture showed a fluctuating upward trend,and air temperature showed a downward trend.The correlation coefficients between temperature,precipitation,soil moisture and annual(growing season)surface greenness(NDVI)were 0.164,0.249and 0.179,respectively.The order of correlation was precipitation>soil moisture>temperature.(3)The results of factor detection showed that the explanatory force of each driving factor to the spatial distinction of surface greenness(NDVI)was in the order of altitude>temperature>vegetation type>precipitation>soil moisture>human disturbance>population density>land use>slope>aspect.Among them,altitude,temperature,vegetation type and precipitation factor are the main driving forces for the spatial heterogeneity of surface greenness in Qinghai Lake Basin,and q-values were 0.427,0.417,0.37 and 0.1,respectively.The remaining factors q-values were below 0.1.In particular,the slope and aspect factor q-values were 0.003 and 0.007,respectively,which had the weakest explanatory force for the spatial distinction of surface greenness(NDVI)in the Qinghai Lake Basin.(4)The results of interactive detection showed that the explanatory force of two-factor interaction on the distionction of surface greenness(NDVI)was greater than that of single factor.The combination of interaction factors with q-value exceeding 0.5 were:temperature and precipitation,temperature and vegetation type,precipitation and altitude,temperature and soil moisture,The interaction q-values were 0.627,0.605,0.589 and 0.500,respectively.The interaction between temperature and precipitation is the main driving force for the spatial distinction of surface greenness in the Qinghai Lake Basin.(5)The risk detection results showed that the classification range or type with the highest NDVI value of the surface greenness(NDVI)of the 10 driving factors were:The annual(growing season)temperature is 3.46-4.78°C,the precipitation in the growing season is 431-456 mm,the soil moisture is 0.34-0.36 m~3/m~3,the vegetation type is valley shrub,the land use type is grassland,the altitude is3488-3652 m,the slope is 0-2.263°,the slope direction is 37-77°,the human disturbance degree is 0.39-0.59,and the population density is 11-68. |
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