Abstract
Multi-year 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 across the globe. 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
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 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.