Modelling Equitable and Reasonable Water Sharing in Transboundary Rivers: the Case of Sirwan-Diyala River

Abstract

There are over 260 transboundary river and lake basins in the world that many of them are facing great challenges of water sharing between riparian countries concerned. The 1997 UN Watercourses Convention, entered into force in 2014, includes articles and factors on water sharing which have not been completely used for modelling of the basins yet. In this paper, legal aspects (i.e. Articles 5, 6, 7 and 10 of the Convention) are integrated with a technical approach for water allocation in transboundary rivers. For this purpose, a new conceptual model is developed for quantification of the Convention provisions concerning equitable and reasonable water sharing. The method is applied to the Sirwan-Diyala transboundary river shared by Iran and Iraq. Some indicators are developed and quantified for determination of water shares of the riparian countries and different scenarios considering extreme and equal weights of the factors are defined. The basin is simulated by WEAP model to evaluate effects of the scenarios on up- and downstream of the basin. Five demand management alternatives comprising increasing of irrigation efficiency and eliminating second cultivation are proposed as appropriate measures for elimination or mitigation of possible significant harm. The proposed technical-legal approach paves the way for enhancing bargaining potentials of the riparian countries and increasing their cooperation to achieve a win-win solution in using waters of transboundary rivers.