Dynamic response of vegetation in Guizhou Plateau under the asymmetric rate of water and heat fluctuation

The Guizhou Plateau is a karst plateau with a fragile ecological environment. Studying the asymmetry of diurnal hydrothermal conditions and its impact on vegetation change can provide theoretical support for ecological protection and disaster reduction. Based on daily temperature and precipitation data obtained from 31 meteorological stations, combined with SPOT satellite image NDVI (normalized difference vegetation index) data, the characteristics and trends of diurnal temperature and precipitation changes were analyzed, and the effects on vegetation activities were discussed using correlation analysis. The results showed that from 1961 to 2017, the annual nighttime precipitation was more than the annual daytime precipitation; however, showed a slight decreasing trend. The annual daytime and nighttime temperature showed increasing trends, with nighttime temperature showing a more significant increasing trend. The average nighttime temperature of each month showed differing increasing trends. NDVI had a closer correlation with temperature than with precipitation. The increase in nighttime temperature promoted the growth of vegetation, while the increase in nighttime precipitation inhibited it. The impact of temperature on vegetation growth in the current month is more significant than that in the previous month or two months. The NDVI in early spring was greatly affected by the nighttime average temperature, while in the early summer, it was greatly affected by the average daytime temperature. There was a two-month lag between NDVI change and diurnal precipitation in the early summer and autumn and between NDVI change and nighttime temperature in early autumn.