Evaluation of flood characteristics within a changing climate in Mpologoma river basin

Abstract

Climate change has a feasible impact on the frequency and magnitude of hydrological extremes. This influences the design of future floodplain structures and water resource plans. The objective of this study was to assess flood characteristics within the Mpologoma River basin for the historical (1980-2009) and future (2010-2040) periods. The HEC-HMS model was used to generate daily flows using Log-Pearson III. The area of inundation was determined using the HEC-RAS model. Using projected rainfall data from General Circulation Models (GCMs), future flood characteristics were determined using projected rainfall data under scenarios RCP4.5 and RCP8.5. Results from the HEC-HMS model calibration and validation indicated a good performance (R2 = 0.75 and R2 = 0.79 respectively) in simulating streamflow, making it suitable for this study. The basin experienced more of the 2-year return floods than the 5-year floods with an increasing trend for both. A consistent increase in stream flow volumes and peak flood magnitudes (coefficient of determination > 98%) in all sub-basins is evident. A significant difference between the historical and the near future flow (p = 0.00001) and an increase in the inundation area and flood return period ranging between 12-15 and 13 16 % under RCP4.5 and RCP8.5, respectively, is observed. Flood frequency, magnitude and inundation area would increase in the future, while floods with 5-year return periods would likely occur in 2028 and 2038 for some GCMs. Continuous observation of discharge for better prediction of flood occurrences and mitigation of their impacts in the basin is recommended.