Propagation of CMORPH rainfall errors to REW streamflow simulation
mismatch in the Upper Zambezi Basin
Abstract
This study investigates propagation effects of CMORPH rainfall
estimation errors on streamflow simulation for a headwater catchment of
the Zambezi River. Model simulations (2006-2012) by the Representative
Elementary Watershed (REW) framework are carried out for uncorrected and
for bias corrected CMORPH product (the Climate Prediction Center
Morphing technique of the National Oceanic and Atmospheric
Administration, or NOAA). As a benchmark to assessments, the model is
run for in-situ observed rainfall obtained from 6 stations at a daily
timestep. Analysis of CMORPH rainfall necessitates bias correction. A
suite of performance indicators indicates that uncorrected CMORPH
estimates show substantial augmentation of rainfall error to streamflow
simulation mismatch whereas bias corrected estimates show attenuation of
error. The ɛ-NSGAII algorithm is selected for single and multi-objective
calibration to assess CMORPH error propagation to REW streamflow
results. Improved hydrograph simulation is achieved by multi-objective
calibration. Flow discharge simulation during the dry season shows more
substantial error attenuation compared to wet season high flow discharge
simulation. Further, this study shows that ratios of model based actual
evapotranspiration over rainfall (ETa/R) and stream flow over rainfall
(Qs/R) (runoff coefficient) at seasonal base change subject to selected
uncorrected and corrected CMORPH. REW water storage (ΔS) is affected as
well as calibrated model parameters. The paper provides new insights on
propagation effects of satellite based rainfall errors in stream flow
modelling.