Implementation of the WA + water accounting system at the basin level and the challenges (Lessons Learned from the Case Study of Tashk - Bakhtegan Basin)

The aim of this paper is to provide an application of Water Accounting Plus (WA+) Framework in the Tashk-Bakhtegan basin based on modification of the Soil Water Assessment Tool (SWAT) model. In this study, it has been provided an analysis of basin conditions in three time periods based on Water Accounting Plus (WA+). The analysis of the results indicates that the Tashk-Bakhtegan basin is a closed basin. In this basin, due to climate change, the manageable water resources have been remarkably declined and unfortunately, not only water managed consumption in the basin (Supplementary Evapotranspiration) have not been reduced but also it has been considerably increased (53%). This has led to a decrease in outflows as the water right supplier of the lake. Moreover, the results indicate an increase in groundwater resources deficiencies and their unsustainable exploitation. Increasing transpiration of plants in agricultural land is another factor influencing the current situation of the Tashk-Bakhtegan basin, due to the expansion of the land area and the increase of high water consuming plants as well as significant contribution of the soil evaporation of the total nonbeneficial consumption of the basin. At the other hand, a significant amount of agriculture water withdrawal is returned to the water basin cycle which emphasizes on “depletion “to “withdrawal” planning.