Impact of land use land cover change on catchment hydrological response in 576 Iranian catchments

Land use and land cover (LULC) changes significantly impact hydrological processes in semi-arid regions like Iran, where national-scale studies are scarce. This study assesses LULC change impacts from 2001 to 2022 on runoff and hydrological drought across Iran's 576 catchments (410,000 km2) using the Soil and Water Assessment Tool Plus (SWAT+). This analysis employs a novel SWAT + framework integrating crop-specific calibrations (e.g., wheat, barley, rice), human interventions (e.g., irrigation, reservoir operations, interbasin diversions), and Curve Number (CN) dynamics, achieving robust performance (NSE: 0.50–0.88; KGE: 0.51–0.90). Evergreen forest loss (4.8 %–2.8 %) and agricultural expansion (20 %–27.8 %) increased annual runoff by 1.21 mm/month, with a 2.7 mm/month rise during the March–May rainy season, driven by 10–15 % reduced canopy interception and 5–10 % CN increases in arid catchments. Hydrological drought frequency rose 15 % in western and central catchments, with duration extending 1.2–1.8 months and severity increasing 5 %, linked to higher surface runoff (1.5–2.7 mm/month). Impacts were pronounced in arid and semi-arid regions (150–300 mm/year precipitation). This study advances LULC impact assessments by integrating runoff and drought analyses with CN dynamics, offering policy strategies like reforestation and precision irrigation for sustainable water management in semi-arid environments.