SPATIOTEMPORAL EVOLUTION AND LAG EFFECT OF DROUGHT AND VEGETATION DYNAMICS IN SOUTHWEST CHINA

In this study, the temporal and spatial characteristics of drought and vegetation dynamics as well as the lag time of vegetation's response to drought in Southwest China were determined. The normalized difference vegetation index (NDVI) and standardized precipitation and evapotranspiration index (SPEI) were used to evaluate the effects of drought on vegetation and determine the response of vegetation to hydrological and climatic changes in different seasons and time scales. The results indicated that from 1970 to 2020, the climate in Southwest China showed a aridity trend with a decreasing rate of 0.024/10a. In autumn, the drought trend intensified, and 90.62% of the study area exhibited a trend toward drought; the most significant drought trend was in Yunnan Province (P < 0.05). On a seasonal level, the NDVI had a downward trend in summer, with a decrease rate of 0.033/10a and an increasing trend in spring, autumn, and winter, with increase rates of 0.016/10a, 0.009/10a, and 0.15/10a, respectively. The areas with the most obvious improvement in vegetation cover were southern Guangxi Province and eastern Sichuan Province, which had the fastest improvement rate, 0.24/10a. The NDVI was most sensitive to the 6 -month SPEI (SPEI_6). The lag time of the NDVI for SPEI at different time scales was 1 month, whereas the lag time for SPEI_6 was up to 2 years. The time delay effect of the NDVI on drought in northwest Sichuan, west Yunnan, southeast Guizhou, and north Guangxi was significantly correlated (P < 0.05). The region with the weakest correlation between the NDVI and SPEI was the agricultural area in eastern Sichuan (P > 0.05). This study provides a crucial theoretical basis for water balance, ecosystem protection, and efficient water resource management in Southwest China