Assessing development and climate variability impacts on water resources in the Zambezi River basin: Initial model calibration, uncertainty issues and performance

Highlights

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  Two hydrological models are established for 76 sub-basins covering the whole of the Zambezi River basin.

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  While both models were successfully calibrated in most areas, there remain a number of uncertainties, mostly related to the available data.

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  The poor simulations for the Shire sub-basins are associated with uncertainties in the observed flow data, as well as the dynamics of Lake Malawi.

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  A further source of uncertainty is related to the interactions of some major tributary river systems with adjacent large wetland areas.

Abstract

Study region

: The Zambezi River basin, one of the most important water resources in sub-Saharan Africa from both a water supply and hydro-power generation perspective.

Study focus

: Calibration of two hydrological models (Pitman and WEAP) that have been established for 76 sub-basins covering the total basin area of about 1 350 000 km ². The longer-term purpose of establishing the models is to facilitate scenario analyses of future conditions related to changes in water use and management as well as climate change.

New hydrological insights for the region

: While there are many (inevitable) uncertainties in the data used, as well as the models and calibrated parameter sets themselves, the results suggest that the models are generally fit for purpose in terms of evaluating future changes. There are, however, some parts of the basin where the reduction of identified uncertainties would lead to improved models and greater confidence in their future use. One of sources of uncertainty relates to the existence of several large wetland areas that have impacts on downstream flows, but are difficult to simulate due to the relatively poor existing understanding of the dynamics of water exchange between the river channels and the wetland storage areas.