The responses of natural vegetation dynamics to drought during the growing season across China

Knowledge of vegetative responses to drought across hydroclimatic zones is crucial for understanding ecohydrologic cycles. Based on monthly self-calibrated Palmer drought severity index (PDSI), standardized precipitation evapotranspiration index (SPEI) at different time scales (1-48 month scales), and normalized difference vegetation index (NDVI), this study examined the relationship between natural vegetation dynamics and drought in the growing season during 1982-2012 at 293 sites over China. Pearson correlations between NDVI and drought indices (PDSI and SPED were employed to quantify the association between vegetation and drought. The results show that the Pearson correlations between PDSI and NDVI in growing season (C-NP) ranged from -0.47 to 0.84, and the maximum correlation between SPEI and NDVI in growing season (MaxSPEI) ranged from -0.31 to 0.86, within which the negative correlations were mainly observed in the areas dominated by forest in south China. Moreover, the C-NP was highly and nonlinearly related to the aridity index (empty set) (MaxSPEI showed a similar trend). The relationship between C-NP and empty set indicated that, water stress was not the limiting factor for natural vegetation in humid regions (empty set < 0.98) even during droughts; the drought vulnerability of natural vegetation increased with increasing empty set up to a point (empty set = 4.68) and then decreased with increasing empty set when empty set > 4.68; in extreme arid regions, the natural vegetation exhibited less sensitivity to drought. These tendencies could be seen worldwide. The varied physiological properties of plants and the response of photosynthesis to energy processes probably explain some discernible variation.