Spatiotemporal variations in fractional vegetation cover and its response to extreme climate events in the Beijing–Tianjin–Hebei region (2001–2023)

Amid ongoing global warming, the frequency and intensity of extreme climate events have markedly increased． Fractional Vegetation Cover (FVC), a critical indicator of ecosystem health, exhibits complex =spatiotemporal dynamics under extreme climatic stress． Understanding these dynamics is essential for improving regional ecosystem management and resilience． This study analyzed monthly maximum-composite FVC data (2001–2023) for the Beijing–Tianjin–Hebei (BTH) region, combined with ERA5 reanalysis datasets． Sen’s trend analysis, correlation analysis, optimal-parameter geographical detector models, and time-lag and accumulation effect analyses were employed to examine the spatiotemporal evolution of FVC and its delayed and cumulative responses to extreme climate indices across three ecological subregions． Results show that: (1) The multi-year mean FVC across the BTH region was 0.61． About 56.74% of the study area exhibited an upward trend in FVC, with 36.34% experiencing statistically significant increases． (2) Daily minimum temperature and consecutive dry days were identified as the main climatic drivers of FVC variation (q > 0.15)． Climatic factors exhibited nonlinear and amplifying interactions, with the combination of consecutive wet days and daily maximum temperature showing the strongest explanatory power (q > 0.42)． (3) Spatially, precipitation-related indices in the northwestern subregion were characterized by a combined 1-month lag and 1-month accumulation effect; the central plain exhibited a dominant 2–3-month accumulation effect; and the eastern coastal zone exhibited persistent multi-month wet accumulation． Temperature-related indices primarily acted through cumulative effects, with lagged responses that were spatially localized．