The application of CHIRPS-based Pitman modelling in South Africa

Abstract

Study regionThe Berg Water Management Area (WMA), drainage region G of South Africa is critical to supplying water for the City of Cape Town and the entire Western Cape region. Study focusDeveloping an approach for the application of CHIRPS-based Pitman modelling in South Africa. CHIRPS-based satellite rainfall data (with a spatial resolution of 0.05° × 0.05°) was used in the Pitman model to simulate observed flows. The model was set up for the Berg WMA which has 35 quaternary catchments and covers an area of approximately 12,965 km2 in assessing the suitability of CHIRPS-based flows. New hydrological insights for the regionThe simulated CHIRPS-based flows using the developed approach indicated 80% suitability of CHIRPS data as an alternative to the dwindling observed rainfall in simulating flows. CHIRPS rainfall data illustrated a strong correlation to observed catchment rainfall and calibration factors were developed for adjustments. Calibration (1981–2009) and validation (2010–2019) statistics indicated a good similarity between observed and CHIRPS-based flows for the period of analysis. The exceedance probability curves for the entire simulation period illustrated similar flow characteristics for the calibration and validation periods. In assessing for uncertainty, hydrological indices were used at a defined ±15% level and the results showed CHIRPS to be suitable. This research recommends the use of CHIRPS-based rainfall data as a suitable alternative in simulating flows for South Africa.