Response of Vegetation Greenness to Extreme Droughts and Possible Mechanisms in Guizhou Province, China

Guizhou Province, China, experienced two extreme drought events during the periods of autumn to spring 2009-2010 and spring to autumn 2011. These events, classified as "one-century drought," led to severe water shortages, significant declines in crop yield, and substantial socioeconomic losses. Despite the evident impact, the heterogeneity of vegetation responses, measured using the Normalized Difference Vegetation Index (NDVI), across different vegetation types and landforms in this region remains insufficiently quantified. Therefore, this study investigates the spatiotemporal evolution of these two events and evaluates the differential NDVI responses of vegetation using multiple climatic datasets and remote sensing-derived vegetation indices. Results indicate that both drought events reached severe levels and persisted for approximately 8 months. The southwestern and western parts of Guizhou Province were hit the hardest. The 2009-2010 drought exerted a more pronounced inhibitory effect on vegetation growth, as evidenced by significantly greater reductions in NDVI during the spring season. Analysis across five major vegetation types showed universal declines in NDVI anomalies, with meadows experiencing the most severe suppression, followed by scrublands, broadleaf forests, and grasslands. Needleleaf forests exhibited the highest drought tolerance. In contrast, the 2011 drought had a comparatively milder impact on vegetation dynamics. Notably, certain vegetation types, particularly broadleaf forests, displayed sustained greening even under drought conditions. Furthermore, vegetation growing on karst landforms exhibited more pronounced declines in greenness compared to those on non-karst landforms, highlighting the influence of geological substrates on drought sensitivity. These findings suggest that under conditions of extreme drought severity, alterations in hydrothermal conditions significantly affect vegetation response patterns across both vegetation types and landform categories. This study provides important insights into the ecological impacts of drought in karst-dominated regions and offers a scientific basis for formulating drought risk management strategies and ecological conservation policies in Guizhou Province.