University of Twente Student Theses


Assessing impacts of climate change and land-use interventions on flooding in Nyabugogo catchment (Kigali -Rwanda)

Umutesi, Mameline (2021) Assessing impacts of climate change and land-use interventions on flooding in Nyabugogo catchment (Kigali -Rwanda).

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Abstract:Flooding is a very common disaster in Rwanda. It is recognized that a sound understanding of the effect of climate change and land use change on extreme hydrological events in catchments is required since such changes heavily affect the hydrological responses of the catchments. This study has assessed the hydrological and flooding behaviors of the Nyabugogo catchment (Kigali-Rwanda) due to land use changes under extreme rainfall due to climate change. The change in climate was analyzed between the period (1981-2005) and (2021-2050) for RCP4.5 and RCP8.5 emission scenarios. With outputs of regional climate models through empirical quantile mapping, corrected future rainfall projections were obtained while the observed rainfall was used for the baseline period. The results for RCP8.5 have shown an increase in monthly rainfall for both the short and long rainy seasons with November being the wettest month of the year. RCP4.5 showed both increase and decrease of rainfall for some months. Annual rainfall was also calculated, and relative to the baseline period, a slight increase was obtained for RCP4.5 while RCP8.5 has shown a considerable increase in the future annual rainfall. The analysis showed that the extreme rainfall events based on the 99th percentile and return periods of 10, 50, and 100-years, these events will become more frequent and increase in magnitude due to climate change under RCP8.5. The results showed that daily extreme rainfall will increase in magnitude under RCP8.5, with 24% while RCP4.5 showed opposite behavior. The increase and decrease of rainfall is associated with to ENSO phenomena which usually influences the extreme events in the region and is expected to influence future climate of the region. The HEC-HMS rainfall-runoff model was used to examine the effect of land use change and climate change on the streamflow hydrograph and peak flows. The results from rainfall-runoff modeling showed that the peak flows will increase with future land use by 29.0%, 37.9% and 45.9% for return periods of 10, 50, 100-years respectively. The increase in peak flows was attributed to the increase of urban runoff response caused by an increase in impervious areas for the future period. Streamflow and peak flows have also increased as a result of climate change for RCP8.5 22.4%, 26.9%, and 29.6% for return periods of 10, 50, 100-years. The RCP4.5 scenario showed a reduction in peak flows with (-25.25, -33.7, and -36.34%) for return periods of 10,50 and 100years respectively. The combined effects of land use change with extreme rainfall for RCP8.5 scenario showed a lager increases in peak flows for Nyabugogo catchment by 61%, 63.3%, 69.6 % for return periods of 10, 50, and 100-years respectively. From the results, was concluded that land-use change has more impacts on streamflow than climate change in the Nyabugogo catchment. The streamflow hydrograph for different scenarios served as inflow boundaries for the flood model. The 1D2D SOBEK hydrodynamic model for the Nyabugogo commercial hub was forced by the boundary inflows from the hydrological model for different scenarios and different return periods. The increase and decrease behaviors observed in extreme rainfall and streamflow and peak flows for land use change, and climate change, respectively were reflected in flooding behavior. For three flood characteristics assessed ( flood water depth, velocity, and flood extent), land use change showed an increase in flooding compared to the present time. The study has concluded that land use change contribute the most to producing more flooding in the Nyabugogo catchment in the future,, while the climate change due to high emission scenario RCP8.5 will take second place. The combined effects of land use and climate change under high emission scenario RCP8.5 exacerbate flooding with a large flood extent. The medium emission scenario RCP4.5 reduced the flooding compared to the current case. This study was the first to assess flooding using the extreme rainfall information from regional climate models for the study area. It was concluded that the RCMs can serve for future flood assessment under a changing climate. Studying the effects of climate change and land-use changes on flooding is useful for water managers for better planning and awareness.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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