Evaluating the effect of the land use change on discharge and flood intensity (case study: sub-basins of Kal-e Shur Sabzevar river basin, Iran)

This research examines the impact of land use changes from 2000 to 2023 on flood regimes and discharge in the Kal-e Shur Sabzevar basin. The study simulated rainfall-runoff processes using PCSWMM and HEC-HMS hydrological models, while the CA-Markov model projected future land use changes. The SCS-CN method was applied to simulate flood hydrographs, and the Muskingum method analyzed river trends. Results revealed notable peak discharge and flood volume increases: 24.6% in 2000, 49.8% in 2010, and 68% in 2020. The study computed maximum flood discharges for various return periods ranging from 2 to 1000 years. The model evaluation showed good accuracy with R2 = 0.97, NSE = 0.85, and PBIAS = 4.22. The HEC-HMS model was remarkably accurate for estimating peak flood discharge for the 100-year return period. Analysis indicates that land use changes, such as the conversion of pasture to agriculture, significantly increase maximum flood discharge and runoff volume. For instance, a 7.6% increase in discharge and runoff was observed for floods with a 500-year return period. Model calibration showed errors between 6.3% for the 100-year return period and 28% for the 2-year return period. Future projections with the CA-Markov model suggest a rise in non-vegetated and agricultural areas by 2050, driven by human activities, which will substantially alter land cover. These insights are valuable for local, national, and international policy development, sustainable land use planning, environmental protection, and flood risk management.