Hydrological risk assessment in the euphrates-tigris river basin: A stochastic dual dynamic programming approach

This paper analyzes the impacts of the Southeastern Anatolia Project(Turkey) on the hydrological regime of the Tigris and Euphrates rivers. The Southeastern Anatolia Project, commonly called GAP, is a Turkish multi-dimensional development project involving primarily irrigation and hydropower generation in the Euphrates and Tigris river basins. For the last two decades, the GAP has been a source of tension between Turkey and the two riparian countries, Syria and Iraq, which are concerned by the modification of the hydrological regime of the Euphrates and Tigris rivers. The quantification of the hydrological risk faced by Syria and Iraq can be comprehended by an integrated management model that simultaneously considers the dispatch of the hydropower plants and the irrigation water withdrawals. The model assumes that the GAP hydroelectric reservoirs are dispatched so as to minimize the operating costs of the Turkish hydrothermal electrical system while meeting irrigation water demands. This optimization problem is solved by a stochastic dual dynamic programming (SDDP) formulation which allows a detailed representation of the Turkish hydrothermal electrical system including the GAP. Scenarios of future irrigation water demands in the GAP are constructed based on projected irrigation areas and on the main crops. Simulation results show that if the project is completed as planned, Euphrates and Tigris outflows will be reduced by 32% and 25% respectively, while the average production of hydroelectricity would reach 2 7 TWh. In addition, Turkey's commitment to deliver a minimum flow of 500 m(3)/s in the Euphrates could only be guaranteed 75% of the time. This percentage increases substantially (up to 95%) if only half of the irrigation projects are implemented.