Comparative Assessment of Hec-Hms and Hec-Hms_Xgboost Models to Simulate Streamflow under Climate Change for Flood Control Structure Design in River Sipi Catchment, Eastern Uganda
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Date
2026
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Busitema University
Abstract
Climate change has significantly intensified the frequency and magnitude of flood events in data-scarce tropical mountainous catchments such as the River Sipi catchment on the slopes, posing serious risks to infrastructure, agriculture, and livelihoods. Conventional physically-based models such as HEC-HMS exhibit critical limitations in capturing the nonlinear, complex dynamics of high-flow peak events under non-stationary climate conditions, compromising the reliability of flood control structure design in such areas. The study comparatively assessed the performance of the conventional HEC-HMS model and a hybrid HEC-HMS_XGBoost model in simulating streamflow under present and future climate scenarios for improved flood control structure design in the Sipi River catchment. The HEC-HMS and the hybrid models utilized historical hydrological data from 2010-2024 for calibration and validation. Future streamflow projections from 2025-2100 were generated by running both calibrated models with bias-corrected and downscaled CMIP6 climate data. Flood frequency analysis using the Gumbel extreme value distribution was applied to derive design discharges Q_10, Q_25, Q_50, and Q_100, which were subsequently used to size four flood control structures: culverts, spillways, bridge waterway openings, and detention basins. The hybrid model substantially outperformed HEC-HMS, achieving NSE values of 0.985 and 0.967 during calibration and validation, with KGE values of 0.934 and 0.893 respectively, compared to unsatisfactory HEC-HMS NSE values of 0.311 and 0.400. Future simulations revealed significantly divergent behavior under SSP5-8.5, HEC-HMS projected a Q_100 of 30.32 m³/s, a 38.5% increase above its Q_10 of 21.89 m³/s, while the hybrid model produced a more stable Q_100 of 21.51 m³/s, only 20.7% above its Q_10 of 17.82 m³/s. Notably, under SSP2-4.5 the hybrid model projected higher discharges than HEC-HMS, providing a physically corrected rather than uniformly lower estimates. Model divergence translated directly into significant structural sizing differences; culvert diameters differed by 14%, spillway crest lengths by 41%, bridge waterway spans by 36%, and detention basin volumes by 59% under SSP5-8.5 Q_100. The study concludes that the HEC-HMS_XGBoost hybrid model provides more reliable, physically plausible, and climate-resilient design discharges than standalone HEC-HMS, and recommends its adoption as the primary basis for flood control structure design in data-scarce tropical mountainous catchments. The standalone HEC-HMS projections under SSP5-8.5 are best reserved as upper-bound safety checks.
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Undergraduate Research Report
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Canwat, E. (2026). Comparative assessment of HEC-HMS and HEC-HMS_XGBoOST models to simulate streamflow under climate change for flood control structure design in River Sipi Catchment, eastern Uganda [Undergraduate research report]. Busitema University.