| The central Yunnan water diversion project is a super large cross-basin water diversion project to solve the serious water shortage problem in central Yunnan,which is also the largest and most invested water resource allocation project in Southwest of China.The water receiving area is distributed in Kunming,Yuxi,Chuxiong,Dali,Honghe and Lijiang.Studying the temporal and spatial distribution and correlation of precipitation and vegetation in the water-receiving area of the central Yunnan water diversion project provides scientific guidance for the cross-regional water resources allocation,which has important scientific value and urgent engineering needs.Based on the 2000-2017 TRMM 3B43 precipitation data,the same period MODIS vegetation data and DEM,this paper uses the scatter slope method,correlation coefficient,relative error to study the accuracy suitabiility of TRMM 3B43.Using Mann-Kendall test,wavelet analysis,MVC,pixel binary model,trend analysis,and spatial correlation analysis analyzes the temporal and spatial distribution of precipitation and vegetation in the water-receiving area of the central Yunnan water diversion project from 2000 to 2017,and further study the correlation between precipitation and vegetation.The main conclusions are as follows:(1)Accuracy analysis of TRMM 3B43 precipitation data.In the annual,seasonal and monthly scales,TRMM 3B43 precipitation has a small deviation and high accuracy in the entire receiving area of the central Yunnan water diversion project and individual stations.The data has good applicability in the receiving area of central Yunnan water diversion project,and provides effective supplements for ground precipitation data.(2)The temporal and spatial distribution and changes of precipitation in the water-receiving area of the central Yunnan water diversion project during 18 years.The annual precipitation in the water-receiving area is unevenly distributed,and the distribution trend is unimodal.Summer precipitation accounts for the largest proportion of annual precipitation,while winter precipitation accounts for a relatively low proportion.The overall level of annual distribution of each station and the fluctuation range of monthly precipitation are all difference.The annual precipitation is reduced by 5.7mm/a.The precipitation in spring and summer shows an obvious downward trend,and the precipitation in autumn and winter is in a slight upward trend.The precipitation decline in the water-receiving area of the central Yunnan Diversion Project has a sudden change in2003.Most of the mutation points of annual precipitation decline at stations are from 2002 to 2003.The water-receiving area of the central Yunnan water diversion project has generally experienced two cycles of high and low precipitation.The spatial distribution of precipitation is heterogeneous and uneven,as a whole shows the phenomenon of "more in the west and less in the east,and more in the south and less in the north",which resulted in more precipitation in two locations,namely the Erhai Lake in Dali City and the Dianchi Lake in Kunming.The decline trend in precipitation continues to expand spatially.(3)The spatial and temporal distribution and changes of vegetation in the water-receiving area of the central Yunnan water diversion project during 18 years.The average NDVI in the receiving area of the central Yunnan water diversion project is between 0.45 and 0.75.The distribution of the NDVI in the receiving area of the central Yunnan water diversion project changes significantly during the year,and the trend is like the cos function.The NDVI reaches the maximum in August;the distribution and overall level of NDVI in each station during the year are also slightly different;the annual maximum NDVI spatial average value of the water-receiving area of the central Yunnan water diversion project from 2000 to 2017 is between 0.74 and 0.80,which shows an upward trend in the study time domain.The maximum NDVI spatial average value in spring is between 0.50 and 0.61,and the maximum NDVI spatial average value in summer is between 0.71 and 0.78.The average value of the maximum NDVI in autumn is between0.71 and 0.77,and the average value of the maximum NDVI in winter is between 0.565 and0.65,both of which are on the rise.The spatial distribution of NDVI is heterogeneous.Among them,the NDVI value of vegetation in the southwest corner of Luchun County,Honghe Prefecture is large,and the vegetation coverage is relatively good.The area of vegetation coverage of various levels in the water diversion area of central Yunnan has fluctuated during 18 years,and the overall vegetation coverage is at a good level.Vegetation coverage in low-altitude areas such as around the Dianchi Lake Basin in Kunming and around Dali City has dropped significantly.(4)The negative correlation between the annual maximum NDVI and annual precipitation in the water-receiving area of the central Yunnan water diversion project is slightly more negative than the positive correlation,and the overall negative correlation accounts for 52.1% of the water-receiving area.The overall reality correlation between spring precipitation and vegetation NDVI is a positive,which accounts for 64.79% of the water-receiving area.The positive correlation between summer precipitation and vegetation NDVI is slightly more than the negative correlation,accounting for 52.56% of the water-receiving area.The correlation between autumn precipitation and vegetation NDVI is slightly more positive than negative,accounting for 60.95% of the water-receiving area.The overall reality of the correlation between winter precipitation and vegetation NDVI is positive,accounting for 99.75% of the water-receiving area.Areas with weak positive correlation and weak negative correlation are relatively large,and most NDVI of the water-receiving area does not change significantly in response to precipitation. |
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