Lagged and cumulative effects of drought on global vegetation greenness, coverage, and productivity

Vegetation dynamics have been greatly altered by the rising frequency of drought events. However, the response of various vegetation characteristics to the lagged and cumulative effects of drought remains poorly understood. Therefore, the lagged and cumulative effects of drought on global vegetation greenness (NDVI), coverage (LAI), and productivity (GPP) were investigated based on diverse vegetation characteristics and standardized precipitation evapotranspiration index (SPEI). And they were analyzed under different water balance gradients, climate zones, and vegetation types. The findings revealed that the lagged response of NDVI to drought was more timely, at 4.29 months. The cumulative response of GPP to drought was more timely, at 4.23 months. Cumulative responses to drought were generally stronger than lagged responses. Across different water balance gradients, the lagged months of NDVI displayed the most significant U-shaped distribution with increasing SPEI, whereas the cumulative months of GPP exhibited the most significant inverted U-shaped distribution. In addition, the arid zone experienced the strongest drought impacts on all vegetation characteristics. Grasslands and shrublands were more vulnerable to drought than forests. Among the three vegetation characteristics, NDVI accounted for the highest percentage of minimum lagged months, at 19.29 %. GPP had the highest percentage of minimum cumulative months, at 15.92 %. This study revealed the complexity of vegetation dynamics under drought stress, which could help us further understand the vegetation response in climate change, and thus provide a critical foundation for ecosystem management and climate change adaptation strategies.