Growing population, increasing basin development, and progressively declining water supplies are typical water resources issues in the Middle East. Drought is one of the most damaging climate-related hazards that affect more people than any other. For identifying drought-prone areas in the Euphrates-Tigris Basin, multifold aspects of drought and its features such as the frequency of drought occurrence and its spatial distribution were assessed. The long-term precipitation data were collected from different meteorological stations of Turkey and Iran, and standard precipitation index (SPI) was calculated. Due to the lack of raw data, the literature works on drought were used in Syria and Iraq to obtain a drought perception in these countries. Moreover, the policy of water resources management and the hydraulic works in these regions were considered. The results show significant changes in the precipitation in these regions over the past decades. The projects undertaken in the basin are not in line with the principles of integrated water resources management and intensify the drought and caused marshland demise in the downstream of the basin. The results of a comprehensive analysis of precipitation variation and water management in this research can alter the policy of water resources management in order to avoid drought in the basin.

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Water withdrawal and changes in hydrologic fluxes have lowered the level of Urmia Lake in Iran, adversely impacting its ecosystem. The continued lowering of the Urmia Lake water level would put Iran's most important aquatic ecosystem in danger of extinction. Therefore, there is an urgent need for management of water withdrawals and for reduction of water use in upstream dams and rivers to halt its continuing decline and allow storage recovery. The Urmia Lake basin was herein modelled with system dynamics (SD) to assess the effects of modifying reservoir operation and water use management on the sustainability of Urmia Lake storage. The model performance was evaluated with the root mean square error (RMSE) and the correlation coefficient (R 2). The results show that SD with RMSE = 18.0 (10 6 m 3) and R 2 = 0.952 is accurate in simulating Urmia Lake storage. Evaluation of the impacts of several scenarios of agricultural water use on lake storage indicates that reductions in the agricultural sector appear inevitable to restore the water balance of Urmia Lake. K E Y W O R D S modelling, system dynamics, Urmia Lake, water demand, water rationing Résumé Les prélèvements d'eau et les changements de flux hydrologiques ont abaissé le niveau du lac Urmia en Iran, affectant négativement son écosystème. La baisse continue du niveau d'eau du lac Urmia mettrait en danger d'extinction le plus important écosystème aquatique d'Iran. Par conséquent, il est urgent de gérer les prélèvements d'eau et de réduire l'utilisation de l'eau dans les barrages et les rivières en amont pour arrêter son déclin continu et permettre la récupération du stockage. Le bassin du lac Urmia a été modélisé ici avec system dynamics (SD) pour évaluer les effets de la modification du fonctionnement du réservoir et de la gestion de l'utilisation de l'eau sur la durabilité du stockage du lac Urmia. La performance du modèle a été évaluée avec l'erreur quadratique moyenne (RMSE) et le coefficient de corrélation (R2). Les résultats montrent que SD avec RMSE = 18.0 (10 6 m 3) et R2 = 0.952 est précis dans la simulation du stockage du lac Urmia. L'évaluation des impacts de plusieurs scénarios d'utilisation agricole de l'eau sur le stockage du lac indique * Dynamique des systèmes appliquée à la gestion de l'eau dans les lacs