Drought Mapping in the Southern Zagros Mountains Using ERA5-Land-Land Reanalysis Data and the Standardized Precipitation-Evapotranspiration Index.

Document Type : Research Paper

Authors

1 Department of Environmental Sciences and Engineering, Faculty of Natural Resources, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran

2 Department of Forestry and Cellulose Industries, Faculty of Natural Resources, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran

Abstract

Drought poses significant threats to water security in mountainous regions, particularly under climate warming. This study maps drought dynamics in the Southern Zagros Mountains (Iran) using ERA5-Land reanalysis data downscaled to 1 km resolution via the TopoPyScale framework, integrating topographic corrections for precipitation, temperature, and potential evapotranspiration (PET). The Standardized Precipitation-Evapotranspiration Index (SPEI) was computed at 3-, 6-, and 12-month timescales to assess meteorological, agricultural, and hydrological droughts from 2000 to 2022. Results reveal strong elevational gradients, with mean annual precipitation ranging from <200 mm yr⁻¹ in southeastern lowlands to >800 mm yr⁻¹ along northwestern ridges, and PET declining from >1500 mm yr⁻¹ to <1200 mm yr⁻¹ with altitude. Spatiotemporal patterns indicate recurrent mild to moderate summer droughts at short timescales, escalating into severe multi-year events (2008–2012, 2018–2021) affecting >60% of the area. Drought frequency is highest (0.45–0.58 events/year) in lowlands, while durations extend to 13–17 months in snow-dependent highlands. Trend analysis shows significant negative SPEI shifts across 45–50% of the region, with slopes of -0.025 to -0.040 per year, driven by warming and increased PET. These findings highlight topography's role in modulating drought vulnerability, offering insights for enhanced water management and climate adaptation in southwestern Iran. The approach demonstrates the value of downscaled reanalysis for precise drought monitoring in complex terrains.

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Desert
Volume 30, Issue 2
December 2025
Pages 434-456

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