Regional water resources assessments using an uncertain modelling approach: The example of Swaziland

Abstract

Study region: The 5 river basins that flow through or within Swaziland in southern Africa. Study focus: A regional water resource assessment using an uncertainty version of the Pitman monthly rainfall-runoff model whose outputs are constrained by six indices of natural hydrological response (mean monthly runoff, mean monthly groundwater recharge, Q10, Q50 and Q90 percentage points of the flow duration curve and% time of zero flows) for each of the 122 sub-basins within the whole of Swaziland. A 2-step approach is adopted where the first step establishes behavioural, but uncertain, model parameter ranges for natural incremental sub-basin hydrological responses, while the second step links all the sub-basin outputs to generate cumulative sub-basin outflows and allows for water use parameters to be included. New hydrological insights for this region: The analysis of hydrological indices highlights the regional variations in hydrological processes and sub-basin response. The adopted modelling approach provides further insight into all of the uncertainties associated with quantifying the available water resources of Swaziland. The study has provided more insight into the spatial variability of the hydrological response and existing development impacts than was previously available. These new insights should provide an improved basis for future water management in Swaziland.

Keywords

• Hydrological response indices
• Uncertainty
• Hydrological modelling
• Swaziland