Analysis on Characteristics and Causes of Temperature and Vegetation Changes in the Middle and Lower Reaches of the Yangtze River After the Three Gorges Dam Operation
Using daily temperature data of 120 stations in the middle and lower reaches of the Yangtze River during 1971-2015,the variations of average temperature before and after the operation of Three Gorges Dam in four seasons (spring,summer, autumn and winter) were analyzed after removing the impacts of global warming background, the mutation times of high and low temperature days were investigated by the MK test method. Furthermore, the change in soil moisture was investigated by utilizing ERA-Interim soil moisture reanalysis data during 2006-2015, and the vegetation response to the temperature variations was analyzed by utilizing MODIS dataset during 2006-2015. The average temperature in the middle and lower reaches of the Yangtze River showed significant changes after the operation of the Three Gorges Dam,warming phenomenon occurred in the southern study area while cooling phenomenon occurred in the northern study area. The MK test results indicated that the high temperature days in the southern study area and low temperature days in the northern study area both mutated around the time when the Three Gorges Dam began to fully operate. Soil moisture obviously increased in the southern study area. The spatial distribution of the enhanced vegetation index (EVI) trend was consistent with the change of the average temperature in spring, summer and winter,the EVI increased in the southern study area, most significantly in winter (33.06%), but decreased in the northern study area,most significantly in summer (5.11%).