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<p>The Satinsyi River Network in Ngororero District has experienced major hydrological and land surface transformations between 2017 and 2023, driven by agricultural expansion, settlement growth, vegetation loss, and increasingly variable rainfall. The basin’s steep slopes, shallow soils, and dominance of low-permeability Hydrologic Soil Groups C and D limit infiltration and intensify surface runoff. This study integrated multi-year Remote Sensing and GIS-based LULC analysis with hydrological modeling in HEC-HMS using the SCS Curve Number framework. Hourly rainfall, runoff, and excess precipitation data from rain gauge stations and HEC-HMS model simulations were used to capture short-duration rainfall extremes and rapid basin responses, while soil texture and HSG mapping informed infiltration and runoff dynamics. Results show substantial LULC shifts: cropland increased from 17454.03Ha (25.73%) in 2017 to 23,23219.29&#xa0;ha (34.23%) in 2023; rangeland declined from 35,691.69&#xa0;ha (52.61%) to 29,949.47&#xa0;ha (44.15%); tree cover decreased from 12,876.01&#xa0;ha to 10,741.40&#xa0;ha; and built-up areas more than doubled from 1,508.08&#xa0;ha to 3,259.09&#xa0;ha. The key findings from the hydrological changes in the Satinsyi River Basin Network based on HEC-HMS simulations, focusing on runoff generation, excess precipitation, and direct flow characteristics revealed that there is an extremely rapid rainfall–runoff response controlled by surface processes. During the major event of 17 November 2020, peak discharges reached 190.7&#xa0;m³/s (S1), 161.8&#xa0;m³/s (S2), 61.1&#xa0;m³/s (S3), 352.6&#xa0;m³/s (R1), and 413.6&#xa0;m³/s at the outlet (Sink-1), reflecting strong downstream flood concentration. Precipitation totaled 10,474.48&#xa0;mm, of which more than 99% became direct runoff. Losses were negligible (32.87–70.18&#xa0;mm), and baseflow was 0&#xa0;mm across all sub-basins, confirming the absence of groundwater contribution. Excess rainfall volumes closely matched discharge volumes (10,416–10,442&#xa0;mm), indicating saturation-excess–dominated behavior over steep slopes and low-permeability soils. Model performance after calibration and validation demonstrates excellent reliability. During calibration (2017–2021), simulated peak discharge at the outlet (387.2&#xa0;m³/s) closely matched observations (348.5&#xa0;m³/s), with NSE = 0.982, KGE = 0.889, and PBIAS = 11.11%. Validation (2022–2023) maintained similar skill (NSE = 0.981, KGE = 0.891, PBIAS = 10.87%) with low error (RMSE = 0.1), confirming strong model transferability under variable conditions. Direct flow analysis indicates moderate but consistent runoff intensity. Mean annual direct flows peaked in 2020 at 9.51&#xa0;m³/s (S1), 8.06&#xa0;m³/s (S2), and 3.04&#xa0;m³/s (S3), aligned with higher effective rainfall. Long-term means were 6.64, 5.63, and 2.13&#xa0;m³/s, respectively, suggesting limited interannual flashiness at annual scale but pronounced event-scale flood peaks during extreme storms. By conclusion, the Satinsyi River Basin functions as a highly runoff-dominated system with minimal infiltration and no baseflow. Extreme rainfall events are rapidly transformed into flood discharges, producing high peak flows at the outlet. These findings underscore the basin’s high flood vulnerability and the critical need for land-use and soil-water conservation measures to attenuate runoff and reduce downstream flood risk.</p>

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Dynamics of land use land cover changes and hydrological responses on runoff in Satinsyi River network of Ngororero District, Rwanda

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月6日

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  • Jean Nepo. Nsengiyumva,
  • Nathan Kanuma Taremwa,
  • John Musemakweri,
  • Hussein Bizimana,
  • J. M. V. Niyigena,
  • Seth Niyitanga,
  • Manasseh Manirakinga,
  • Phenias Mukiza,
  • Marie Jeanne Umuhoza

摘要

The Satinsyi River Network in Ngororero District has experienced major hydrological and land surface transformations between 2017 and 2023, driven by agricultural expansion, settlement growth, vegetation loss, and increasingly variable rainfall. The basin’s steep slopes, shallow soils, and dominance of low-permeability Hydrologic Soil Groups C and D limit infiltration and intensify surface runoff. This study integrated multi-year Remote Sensing and GIS-based LULC analysis with hydrological modeling in HEC-HMS using the SCS Curve Number framework. Hourly rainfall, runoff, and excess precipitation data from rain gauge stations and HEC-HMS model simulations were used to capture short-duration rainfall extremes and rapid basin responses, while soil texture and HSG mapping informed infiltration and runoff dynamics. Results show substantial LULC shifts: cropland increased from 17454.03Ha (25.73%) in 2017 to 23,23219.29 ha (34.23%) in 2023; rangeland declined from 35,691.69 ha (52.61%) to 29,949.47 ha (44.15%); tree cover decreased from 12,876.01 ha to 10,741.40 ha; and built-up areas more than doubled from 1,508.08 ha to 3,259.09 ha. The key findings from the hydrological changes in the Satinsyi River Basin Network based on HEC-HMS simulations, focusing on runoff generation, excess precipitation, and direct flow characteristics revealed that there is an extremely rapid rainfall–runoff response controlled by surface processes. During the major event of 17 November 2020, peak discharges reached 190.7 m³/s (S1), 161.8 m³/s (S2), 61.1 m³/s (S3), 352.6 m³/s (R1), and 413.6 m³/s at the outlet (Sink-1), reflecting strong downstream flood concentration. Precipitation totaled 10,474.48 mm, of which more than 99% became direct runoff. Losses were negligible (32.87–70.18 mm), and baseflow was 0 mm across all sub-basins, confirming the absence of groundwater contribution. Excess rainfall volumes closely matched discharge volumes (10,416–10,442 mm), indicating saturation-excess–dominated behavior over steep slopes and low-permeability soils. Model performance after calibration and validation demonstrates excellent reliability. During calibration (2017–2021), simulated peak discharge at the outlet (387.2 m³/s) closely matched observations (348.5 m³/s), with NSE = 0.982, KGE = 0.889, and PBIAS = 11.11%. Validation (2022–2023) maintained similar skill (NSE = 0.981, KGE = 0.891, PBIAS = 10.87%) with low error (RMSE = 0.1), confirming strong model transferability under variable conditions. Direct flow analysis indicates moderate but consistent runoff intensity. Mean annual direct flows peaked in 2020 at 9.51 m³/s (S1), 8.06 m³/s (S2), and 3.04 m³/s (S3), aligned with higher effective rainfall. Long-term means were 6.64, 5.63, and 2.13 m³/s, respectively, suggesting limited interannual flashiness at annual scale but pronounced event-scale flood peaks during extreme storms. By conclusion, the Satinsyi River Basin functions as a highly runoff-dominated system with minimal infiltration and no baseflow. Extreme rainfall events are rapidly transformed into flood discharges, producing high peak flows at the outlet. These findings underscore the basin’s high flood vulnerability and the critical need for land-use and soil-water conservation measures to attenuate runoff and reduce downstream flood risk.