Modeling for transboundary water resources planning and allocation

Abstract

International water resources agreements for transboundary rivers in southern Africa are based on system analysis models for water planning and allocation. The Wa- ter Resources Yield Model (WRYM) developed in South Africa has so far been the 5 only model applied in official joint water resources studies aimed to form water-sharing agreements. The continuous discussion around the model performance and grow- ing distress over it being South African, where it was originally developed, while South Africa is one of the interested parties in the process, results in an increased controversy over the system analysis results that are often only meant to guide in selecting the op- 10 tions for water resources management in a given set of scenarios. The objective of this study was therefore to assess the model performance of two other models; WAFLEX and WEAP21 in the Umbeluzi River Basin system where the WRYM was previously applied as part of a Joint River Basin Study. A set of basin development scenarios was equally tested in the three models and the results compared. The results show that 15 the three models all are possible tools for system analysis of river basins in southern Africa, although the structure and complexity of the models are different. The obtained level of satisfaction for specific water users could, however, vary depending on which model was used, which causes uncertainties. The reason for the diverse results is the structurally different ways of describing allocation and prioritization of water in the three 20 models. However, the large degrees of freedom in all system models cause even larger uncertainty in the results since the model user can, intentionally or unintentionally, di- rect the results to favor certain water users. The conclusion of this study is therefore that the choice of model does not per se affect the decision of best water allocation and infrastructure layout of a shared river basin. The chosen allocation and prioritization 25 principles for the specific river basin and the model user’s experience and integrity are more important factors to find the optimal and equitable allocation. 476 HESSD