Water Balance Study for the Tigris-Euphrates River Basin

Abstract

Several case studies of the Tigris-Euphrates (TE) river basin were performed to investigate the effects of various water resource utilizations on dynamic water balances of the watershed. A daily dynamic water balance model was developed to simulate water resource conditions corresponding to four utilization scenarios in the TE watershed: (1) pre-1970 natural conditions; (2) current levels of water resource development/utilization in Syria and Iraq while maintaining pre-1970 conditions in Turkey (i.e., natural, unobstructed flows from Turkey); (3) scenarios involving constant-discharge water release from the Turkish sector downstream on the basis of estimations of future water utilization in the Turkish sector of the TE watershed; and (4) minimum time-varying water releases from Turkey to meet current irrigation water demands in the downstream region. All water balance simulations reconstructed atmospheric and hydrologic conditions during historical critical drought and flood periods. Irrigation demands were estimated by using the Food and Agricultural Organization of the United Nations (FAO) method, with reconstructed atmospheric and crop distribution data derived from satellite observations. Operations of 15 major dams in the Syrian and Iraqi sectors of the TE watershed were dynamically simulated under several different flow regimes regulated and unregulated by the upstream country, Turkey. This study illustrates that irrigation water demands in Iraq and Syria can be effectively met by various constant-discharge water releases from the Turkish sector. Also, if the seasonality of irrigation water demands in the lower TE region is considered when scheduling water releases from Turkey, these releases can be decreased while still meeting the current irrigation water demands of downstream countries. Water diversion from the Tigris to the Euphrates through the Samarra-Thartar complex may provide significant freedom to optimize water allocation in this region. Additionally, because of the arid climate in the lower TE river basin, a considerable amount of water evaporates from the reservoirs. The analyses indicate that storing water in the upstream region seems to be more effective in reducing reservoir water evaporation compared to storing water in the downstream region because the small surface area-to-storage volume of the upstream TE reservoirs and the cooler climate in the upstream sector of the watershed.