Parameter and input data uncertainty estimation for the assessment of water resources in two sub-basins of the Limpopo River Basin

摘要

The demand for water resources is rapidly growing, placing more strain onaccess to water and its management. In order to appropriately manage waterresources, there is a need to accurately quantify available water resources.Unfortunately, the data required for such assessment are frequently far fromsufficient in terms of availability and quality, especially in southernAfrica. In this study, the uncertainty related to the estimation of waterresources of two sub-basins of the Limpopo River Basin – the Mogalakwena inSouth Africa and the Shashe shared between Botswana and Zimbabwe – isassessed. Input data (and model parameters) are significant sources ofuncertainty that should be quantified. In southern Africa water use data areamong the most unreliable sources of model input data because availabledatabases generally consist of only licensed information and actual use isgenerally unknown. The study assesses how these uncertainties impact theestimation of surface water resources of the sub-basins. Data on farmreservoirs and irrigated areas from various sources were collected and usedto run the model. Many farm dams and large irrigation areas are located inthe upper parts of the Mogalakwena sub-basin. Results indicate that water useuncertainty is small. Nevertheless, the medium to low flows are clearlyimpacted. The simulated mean monthly flows at the outlet of the Mogalakwenasub-basin were between 22.62 and 24.68 Mm3 per month whenincorporating only the uncertainty related to the main physical runoffgenerating parameters. The range of total predictive uncertainty of the modelincreased to between 22.15 and 24.99 Mm3 when water use datasuch as small farm and large reservoirs and irrigation were included. For theShashe sub-basin incorporating only uncertainty related to the main runoffparameters resulted in mean monthly flows between 11.66 and 14.54 Mm3. The range of predictive uncertainty changed to between 11.66and 17.72 Mm3 after the uncertainty in water use informationwas added.