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  • Hydrol. Earth Syst. Sci., 14, 23432354, 2010www.hydrol-earth-syst-sci.net/14/2343/2010/doi:10.5194/hess-14-2343-2010 Author(s) 2010. CC Attribution 3.0 License.

    Hydrology andEarth System

    Sciences

    Modeling for transboundary water resources planning andallocation: the case of Southern Africa

    D. Juzo1 and R. Liden2

    1Universidade Eduardo Mondlane, Faculdade de Engenharia, Av. de Mocambique, CP 257, Km 1.5, Maputo, Mocambique2Lund University, Department of Water Resources Engineering, P.O. Box 118, 22100 Lund, Sweden

    Received: 9 January 2008 Published in Hydrol. Earth Syst. Sci. Discuss.: 19 February 2008Revised: 6 October 2010 Accepted: 15 November 2010 Published: 26 November 2010

    Abstract. International water resources agreements fortransboundary rivers in southern Africa are generallyfounded in system analysis models for water planning and al-location. The Water Resources Yield Model (WRYM) devel-oped in South Africa has so far been the only model appliedin official joint water resources studies aimed to form water-sharing agreements. The continuous discussion around themodel performance and growing distress over it being SouthAfrican, where it was originally developed, while SouthAfrica is one of the interested parties in the process, resultsin an increased controversy over the system analysis resultsthat are often only meant to guide in selecting the optionsfor water resources management in a given set of scenarios.The objective of this study was therefore to assess the modelperformance of two other models; WAFLEX and WEAP21in the Umbeluzi River Basin system where the WRYM waspreviously applied as part of a Joint River Basin Study. Aset of basin development scenarios was equally tested in thethree models and the results compared. The results show thatthe three models all are possible tools for system analysisof river basins in southern Africa, although the structure andcomplexity of the models are different. The obtained levelof satisfaction for specific water users could, however, varydepending on which model was used, which causes uncer-tainties. The reason for the diverse results is the structurallydifferent ways of describing allocation and prioritization ofwater in the three models. However, the large degrees of free-dom in all system models cause even larger uncertainty in theresults since the model developer can, intentionally or unin-tentionally, direct the results to favor certain water user. Theconclusion of this study is therefore that the choice of modeldoes not per se affect the decision of best water allocationand infrastructure layout of a shared river basin. The chosen

    Correspondence to: D. Juzo([email protected])

    allocation and prioritization principles for the specific riverbasin and the model developers experience and integrity aremore important factors to find the optimal and equitable al-location.

    1 Introduction

    Water resources systems are generally complex with bothqualitative and quantitative factors governing water resourcesavailability (Raju and Pillai, 1999). In southern Africa thehigh climatic variability further adds the complexity. Boththe large seasonal variations and the interannual variations,with long dry spells, make infrastructural solutions necessaryto assure water availability at all times. The role of reservoirsin water resources management in Southern Africa is high-lighted by van der Zaag and Bolding (2005).

    However, building infrastructures will not on its own en-sure water availability and equitable water allocation be-tween countries and users of a particular river basin. Thesystem of natural and regulated water resources should beutilized and managed appropriately for sustainable use ofthe water resources. In southern Africa, decision on wa-ter resources permit allocation between different users andbetween different riparian countries is therefore commonlybased on system analysis tools. System analysis tools are ad-equate to evaluate and propose the best management strate-gies towards maximization of benefits for a given number ofusers under given objective functions in the catchment. Aspointed out by Dent (2001) ... a model is a tool to help or-ganize a negotiation or learning process in which its primaryfunction is to provide a framework for thinking by enablingparticipants to make their implicit assumptions explicit in asystematic manner. Despite being a simplification of a com-plex water resources system, a system analysis model givesthe opportunity for decision makers to know beforehand theconsequence of a chosen management option or scenario,

    Published by Copernicus Publications on behalf of the European Geosciences Union.

    http://creativecommons.org/licenses/by/3.0/

  • 2344 D. Juzo and R. Liden: Modeling for transboundary water resources planning and allocation

    though, within the limits imposed by the uncertainty in dataand gaps in the knowledge of the processes involved in natu-ral systems. These tools are therefore important instrumentsfor authorities and governments to adopt policies for waterresources management in both national and transboundaryriver basins. However, because the stakeholders or countriesobjectives often are conflicting it is necessary that the modelor software used is considered unbiased.

    In southern Africa the countries have not yet agreed on theset of decision support tools that should apply in the waterallocation process. The experience from the already imple-mented joint system analysis studies in Umbeluzi and Inco-mati rivers in southeast Africa (Consultec and BKS Acres,2000; SWECO and Associates, 2005) has shown preferenceto the Water Resources Yield Model (WRYM) as the tooladopted for system analysis. The experience from these stud-ies, however, shows that the results obtained from WRYMare not easily understood by the stakeholders, and govern-ment representatives of different countries bear some suspi-cion about the results from the system analysis. The lackof trust in the system analysis tool has prevented a smoothnegotiation on transboundary water resources allocation, fo-cusing the discussion on the nature and properties of the toolsrather than the strategies that can be applied to improve waterresources allocation between countries.

    Water resources system analysts are challenged to producea system analysis model that considers both the legal frame-work and the true behavior in the system. Stakeholders of-ten share water resources at very local level and rely mostlyon customary principles embodied in local level institutions(van der Zaag and Bolding, 2005). Integrating small stake-holders in a large-scale river basin management thus needsharmonization of local and regional interests. In the case awater release in a large basin targets the most downstreamuser, e.g. environment flow to the estuary, all the local wa-ter users along the river must have a corresponding objec-tive not to use this water, otherwise the reserved water willgradually be used by the local users starting with the mostupstream community. This situation is even more difficult intransboundary rivers. In such a situation the question is: howcomplex should a system analysis model be to handle thisscale problem but at the same time be sufficiently transpar-ent and uncomplicated to give stakeholders information forsetting and accepting allocation criteria?

    This study examines the role that decision support toolsplay in the agreement process by evaluating three differ-ent system analysis model packages for water allocation forthe same river basin, the Umbeluzi River in Swaziland andMozambique. The objective is to compare these models interms of complexity, reliability of results, transparency andto assess whether the model selection may affect the deci-sion of best water allocation and infrastructure layout of ashared river basin.

    2 Material and methods

    Because the WRYM is the preferred model tool for sys-tem analysis of international river basins in the SADC re-gion (Carmo Vaz and van der Zaag, 2003; van der Zaag andCarmo Vaz, 2003) a comparative analysis of model perfor-mance was conducted through applying two other modelsin a river basin where the WRYM had been applied. As acase study it was chosen to do the assessment in the Um-beluzi River in which the WRYM has previously been setup as part of the Joint Umbeluzi River Basin Study (JU-RBS) that aimed to prepare the baseline for a new water re-sources sharing agreement between Swaziland and Mozam-bique (SWECO and Associates, 2005). The Umbeluzi Riverbasin was chosen because it is a relatively simple water re-sources system which is faced with some of the core chal-lenges of transboundary rivers in southern Africa: high cli-matic variability, scarce water resources, upstream versusdownstream users, large-scale versus small-scale users andsignificant environmental flow requirements. The challengesfor water resources management in the Umbeluzi River basinhave previously been studied by Juizo et al. (2006).

    The basis for the study was that the different models wouldapply the same inputs and configuration as was used in thestudy by SWECO and Associates (2005). As a first step theWRYM model runs by SWECO and Associates (2005) werereproduced to simulate a set of different development sce-narios for the Umbeluzi River basin. Secondly a spreadsheetbased system analysis model, WAFLEX, and a correspond-ing GIS based software, WEAP21, were set up for the Um-beluzi River and applied for the same development scenarios.The WAFLEX model has been used previously in analyzingother river basins in SADC region, namely the Incomati, Ma-puto and Save (Nkomo and van der Zaag, 2004; Sengo et al.,2005; de Groot and Oosterwijk, 2006; Symphorian et al.,2003). While the WEAP21 was used in the Olifants river atributary to Limpopo river (Levite and Sally, 2002; Le Roy,2005).

    2.1 The Umbe

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