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Hydrological response of semi-arid watersheds to isolated land cover–land use transitions: loss of natural regulation and increased flood risk
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DOI：10.3389/frwa.2026.1805169.png)
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Abstract
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IntroductionThe hydrological regime of a watershed can be substantially altered by transitions in its land cover-land use (LCLU); particularly in arid and semi-arid regions; where changes in soil and vegetation cover directly influence surface runoff generation. Accordingly; this study investigated the hydrological response to isolated LCLU changes in the Gorganrood Watershed (GW); located in the semi-arid environment of northeastern Iran; using the Soil and Water Assessment Tool (SWAT).MethodsTo attribute such hydrological variations specifically to long-term LCLU transitions; the SWAT model was configured with four historical LCLU datasets (1975; 1988; 2001; and 2014); while all other input data; including climate; were held constant. This modeling framework enables a robust attribution of hydrological changes solely to LCLU transitions; addressing a key limitation of previous studies that assessed combined climate and LCLU effects.ResultsThe SWAT model performed satisfactorily in simulating daily discharge across the GW and its five sub-basins (Galikash; Gonbad; Haji-ghushan; Tamar; and Tangrah) during both the calibration (1986–2000) and validation (2001–2010) periods; with R2 values ranging 0.73–0.82 and 0.69–0.76; respectively. The significant LCLU transitions across the GW over 1975–2014 involved large-scale expansion of farmlands; contraction of rangelands; forest loss; and progressive urbanization. In response; substantial increases of 6.69% and 16.30% in simulated mean and maximum daily discharge; respectively; reflect a shift toward a more surface runoff-dominated hydrological regime within the watershed. Spatially; steep upland sub-basins (e.g.; Tangrah) were more sensitive to LCLU-driven discharge changes than the lower-elevation sub-basins (e.g.; Gonbad); which showed the highest absolute flows.DiscussionThese findings provide hydrological evidence of degraded natural regulation capacity under LCLU transitions and emphasize the importance of integrating LCLU management strategies; including Nature-Based Solutions (NbS) such as soil structure restoration and reforestation; into climate adaptation planning to reduce flood risk in semi-arid watersheds worldwide.
Keywords:
Iran
SWAT
deforestation impacts
discharge sensitivity
flood risk mitigation
rangeland conversion
semi-arid basins
surface runoff dynamics
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