Hydrologic evaluation of bias corrected CMORPH rainfall estimates at the headwater catchment of the Zambezi River

Abstract

Uncorrected and bias corrected CMORPH satellite-based rainfall estimates were evaluated for application in the Representative Elementary Watershed (REW) modelling approach in the Kabompo Basin, a headwater catchment of the Zambezi River. Results of modelling (2008–2013) by use of raingauge rainfall served as benchmark to the simulation results. The uncorrected CMORPH rainfall show overestimation (>20%) and underestimation (<−15%) biases for the 2000–2015 period. A linear-multiplicative bias correction scheme was applied to remove the bias. When applied to the REW model, bias corrected CMORPH rainfall improved the match between observed and simulated streamflow. Improvements in streamflow simulation are reported for highest discharges and streamflow totals. Objective function values for Relative Volume Error and for Nash Sutcliffe Efficiency improved significantly by the bias correction. Errors in uncorrected CMORPH rainfall estimates cause large mismatch between simulated and observed streamflow, however mismatch reduces notably for bias corrected satellite rainfall. Optimized REW parameter values changed by > 50% when gauge-based rainfall inputs are replaced by uncorrected CMORPH estimates. However, parameter values, remained within physically acceptable ranges for bias corrected CMORPH, for intermediate flows and for the wet season. This study shows that bias correction of CMORPH rainfall in the Kabompo Basin is critical for successful application in rainfall-runoff modelling.