Vegetation Response to Meteorological and Agricultural Drought and Drought Propagation Characteristics in the Sub-Humid and Semi-Arid Regions of Northern China

The response mechanisms of vegetation to drought vary significantly depending on both drought and vegetation types. Clarifying the propagation process from meteorological drought (MD) to agricultural drought (AD) and its impact on vegetation is of great significance for ecological barrier protection in China. Focusing on the sub-humid and semi-arid regions of Northern China, this study analyzes the time effect and driving factors of vegetation response to MD and AD, while quantifying the drought propagation time (DPT) during 1982–2020. The results indicate that: (1) Across the study area, MD response follows a "short lag-short cum" pattern, while AD exhibits "long lag-short cum" pattern. Compared to sub-humid regions, all vegetation types and forest sub-types in semi-arid regions show a "high sensitivity-high tolerance" pattern toward MD, while exhibiting a "delayed response-low tolerance" pattern toward AD. (2) Regarding MD, shrubland is the most sensitive, while grassland exhibits the highest tolerance; additionally, the drought tolerance of needleleaf forests exceeds that of broadleaf forests. Regarding AD, forests show the highest sensitivity and the strongest tolerance, with broadleaf forests responding more rapidly than needleleaf forests. (3) Significant soil hydrological buffering exists, with 51.8% of vegetation and 53.4% of forest regions exhibiting an 8–9 month DPT. Semi-arid response patterns align with the whole study area (grassland < forest < cropland < shrubland). Broadleaf is consistently shorter than needleleaf across the entire study area, as well as in sub-humid and semi-arid regions. (4) Among the driving factors of vegetation response to drought, temperature (TMP), precipitation (PRE), potential evapotranspiration (PET), and vapor pressure deficit (VPD) rank as the top three in importance. TMP dominates the lagged effects of vegetation response to both MD and AD, whereas PRE determines the cumulative effects for both drought types.