Environmental drivers of drought effects on vegetation growth across Southwest China: Insights from an integrated...

Drought, intensified by global climate change, is increasingly reshaping terrestrial ecosystem functioning and threatening vegetation stability worldwide. Although numerous studies have documented drought impacts on vegetation dynamics, progress remains limited in quantifying the magnitude of drought impacts on vegetation growth and disentangling their environmental controls across heterogeneous landscapes. Here, we developed an integrated framework that combines soil moisture thresholds with response ratio-based effect size to quantify drought-induced vegetation decline relative to non-drought conditions and to identify dominant drivers across geological regions and vegetation types in Southwest China. Results showed that vegetation growth declined by an average of 14.2% when soil moisture fell below thresholds, with stronger reductions in karst regions (-15.6%) than in non-karst areas (-12.5%), reflecting weaker hydrological buffering and limited water storage capacity in karst landscapes. Among vegetation types, grasslands exhibited the largest reduction (-26.3%), followed by croplands and shrublands, whereas forests showed the smallest reduction (-12.5%), indicting greater resistance to moisture stress. Attribution analysis showed that precipitation variability (P_cv), drought frequency (DF), and fractional vegetation cover (FVC) mitigated vegetation decline, whereas stronger radiation and higher clay fraction exacerbated drought stress by increasing atmospheric demand and constraining soil water availability. Significant contrasts in soil properties and FVC between geological settings indicate stronger soil-water constraints and greater vegetation dependence in karst ecosystems. Further analyses across vegetation types demonstrated that croplands were more responsive to environmental drivers, whereas grasslands were more vulnerable to recurrent drought events. This integrated soil moisture threshold and effect size framework provides a scalable diagnostic approach for quantifying drought impacts on vegetation across environmental gradients and offers mechanistic insights for ecosystem management and climate adaptation under intensifying hydroclimatic extremes.