Analysis of effective environmental flow release strategies for Lake Urmia restoration

Abstract Saline lakes have diminished considerably due to large-scale irrigation projects throughout the world. Environmental flow (EF) release from upstream reservoirs could help conserve and restore these lakes. However, experiences from regions lacking environmental legislation or with insufficient water resources management show that, despite EF allocation, farmers tend to use all available water for agriculture. In this study, we employed a new method for designing environmental flow release strategies to restore desiccated terminal lakes in arid and semi-arid regions with intensive cultivation within the catchment. The novelty of the method is that it takes into account farmers’ water use behavior and the natural flow regime in upstream systems to design an optimum monthly EF release strategy for reservoirs. We applied the method to the water resource system of Lake Urmia, once the largest saline lake in the Middle East and now one of the most endangered saline lakes in the world. The analysis showed that the EF released is exploited by lowland farmers before reaching Lake Urmia and that inflow to the lake from some rivers has decreased by up to 80%. We propose a new EF release strategy that requires a considerable change in practice whereby water is released in the shortest possible time (according to reservoir outlet capacity) during the period of lowest irrigation demand in winter. Restoring the lake to minimum ecological level would require 2.4–3.4 km³ EF allocation by different methods of release based on the recent condition (2002–2011) of the lake