Heterogeneous Influences of Driving Factors on the Propagation from Meteorological Drought to Agricultural and Ecological Droughts

Droughts cause significant impact on the terrestrial vegetation ecosystem with water shortage propagating through ecohydrological processes. Understanding how drought affects the ecosystem under different hydrogeological conditions is crucial for ecosystem protection. However, it is not clear how ecosystems respond to meteorological drought (MD) under different hydrogeological conditions. This study used monthly standardized precipitation evapotranspiration index (SPEI), soil moisture index (SSMI), normalized difference vegetation index (SNDVI) and solar-induced chlorophyll fluorescence (SSIF) to investigate the characteristics and mechanisms of propagation from MD to agricultural drought (AD) and ecological drought (ED) during 2000~2014 in the Jinsha River Basin. Based on the maximum correlation coefficients (MCC), the differences in drought propagation time of MD to AD and ED were explored in positively and negatively correlated areas. Random Forest was used to identify the impacts of driving factors on drought propagation. Results show that (1) AD was mainly positively correlated with MD while the correlation coefficients between ED and MD ranged from negative to positive. (2) The propagation time from MD to AD was shorter in summer and autumn. The propagation time from MD to ecological drought indicated by NDVI (EDndvi) was shorter than that to ecological drought indicated by SIF (EDsif) in the positively correlated areas while the result in the negatively correlated areas was in contrast. (3) Random forest results indicated that temperature (T), solar radiation (S) and precipitation (P) were key factors influencing ED in positively correlated areas, T was an important factor in controlling the occurrence of ED in negatively correlated areas. (4) SIF was more sensitive to MD and had a shorter response time in positively correlated areas. It has great potential for monitoring the response of vegetation growth to drought. MD is not the main factor threatening vegetation growth in negatively correlated areas. The findings in this study have significant implications for accurately understanding the mechanisms of the response of vegetation growth to meteorological drought and offer scientific guidance for maintaining terrestrial ecosystem health.