Thrive or Wither: Exploring the Impacts of Multiyear Droughts on Vegetation

Abstract

Multiyear droughts (MYDs), droughts lasting over a year, can have devastating effects on vegetation. Due to climate change, MYDs are expected to become more frequent and intense, making it crucial to assess and understand their impact on vegetation. In this study, we used ERA5 reanalysis and MODIS remote sensing data to assess vegetation drought sensitivity and quantify the impact of MYDs on seven different vegetation types in specific regions worldwide. We first assessed drought sensitivity by calculating the enhanced vegetation index (EVI) anomaly across different drought timescales. Then, we evaluated the impact of MYDs and normal droughts (NDs) by averaging the EVI anomaly during their respective drought periods. Our analysis shows that croplands, urban areas, and shrublands are highly drought-sensitive, while grasslands and trees are less so. As anticipated, the overall impact of MYDs on vegetation was negative, but there were significant spatial and temporal variations, with some areas showing greening. In general, shrublands experienced the largest decrease in greenness, while needle-leaved trees flourished. Natural water availability was the primary factor influencing vegetation response to MYDs. Vegetation in water-limited areas tends to suffer during MYDs, whereas vegetation in energy-limited areas thrives as long as sufficient water is available. Compared to NDs, MYDs typically have a slightly more negative impact on vegetation. Overall, these findings show that there is no unidirectional vegetation response to MYDs and that local factors, like natural energy and water availability, play a vital role in quantifying the complex interplay between drought and its impacts on vegetation.