Historical Drought Variability in Neotropical Dry Forests Using the Standardized Precipitation Evapotranspiration Index (SPEI) from 1950 to 2024

Tropical dry forests (TDFs) are ecosystems that are highly vulnerable to drought and face threats from human activities. However, long-term assessments of ecological drought dynamics across their geographic extent remain limited. In this study, we quantify spatial and temporal drought patterns in TDFs across the Americas using the Standardized Precipitation Evapotranspiration Index (SPEI). We examined SPEI at 3-, 6-, and 12-month timescales to capture short-term moisture deficits and longer-term water stress affecting ecosystem functioning. Drought trends from 1950 to 2024 were analyzed, focusing on drought occurrences, their severity, duration, and spatial extent.

Our results reveal heterogeneity in drought dynamics across the Neotropical dry forests. While some areas have experienced increases in drought severity and persistence in recent decades, longer SPEI timescales indicate an intensification of prolonged water deficits, particularly in regions with higher precipitation regimes. Overall, this study provides a continental-scale perspective on ecological drought in TDFs in the Neotropics. It highlights emerging hotspots of vulnerability and emphasizes the importance of incorporating evaporative demand into drought assessments. Our findings have direct implications for understanding ecosystem resilience, guiding conservation strategies, and predicting climate change impacts on tropical dry forest structure and function.