Determining Hydrological Variability Using a Multi-Catchment Model Approach for the Western Cape, South Africa

Andrew Watson,Sven Kralisch,Jörg Helmschrot,Annika Künne,Guy Midgley

doi:10.3390/su132414058

Andrew Watson, Sven Kralisch + Show 3 more

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https://doi.org/10.3390/su132414058

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Abstract

Understanding the impacts of climate change requires the development of hydrological modelling tools. However, data scarcity hinders model application, performance, process simulation and uncertainty, especially for Sub-Saharan Africa. In this study, a multi-catchment approach was used to assess hydrological process variability in the Western Cape (WC) of South Africa using the JAMS/J2000 rainfall–runoff model and a Monte Carlo analysis (MCA). Due to much steeper slopes and lower evapotranspiration, the models suggest that WC is dominated by surface runoff from mountainous regions and regional groundwater flow. The results highlight the impact of the catchment size, availability and position of hydroclimatic and anthropogenic factors and the frequency of the signal-to-noise ratio (water balance). For large catchments (>5000 km2), the calibration was able to achieve a Nash–Sutcliffe efficiency (NSE) of 0.61 to 0.88. For small catchments (<2000 km2), NSE was between 0.23 to 0.39. The large catchments had an overall surface runoff, interflow and baseflow contribution of 44, 19 and 37%, respectively, and lower overall uncertainty. The simulated flow components for the small catchments were variable and these results are less certain. The use of a multi-catchment approach allows for identifying the specific factors impacting parameter sensitivities and in turn provides a means to improve hydrological process simulation.

Highlights

Climate change is altering the distribution and nature of precipitation patterns around the world, driving hydrological change and exacerbating the loss of natural ecosystems [1].As a consequence, hydrological flows are projected to change on a global scale [2,3], with changes in streamflow patterns and expected alterations to the flow components thereof
The results include the analysis of the precipitation amount and characteristics and the resulting observed streamflow of each catchment, as well as the simulated streamflow, simulated hydrological flow components, the simulated water balance and the sensitivity of each parameter for the selected study catchments
Hydrological flows in the Western Cape (WC), and for the Berg and Breede simulation, were dominated by mountainous regions where surface runoff is generated from higher average precipitation and the steep slopes of the Table Mountain Group (TMG) (Figure 8)

Summary

Introduction

Hydrological flows are projected to change on a global scale [2,3], with changes in streamflow patterns and expected alterations to the flow components thereof (surface runoff, interflow and baseflow) These flow components are subject to seasonal variations, but during periods of peak or high flow, surface runoff and interflow are often more significant [4], while during periods of low flow, baseflow is more dominant [5]. The proportion of these flow components depends on climate, land use, surface terrain, subsurface conditions and drainage characteristics [6], as well as anthropogenic water use [7].

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