Basin-wide water accounting based on modified SWAT model and WA plus framework for better policy making

Evaluation of water resources systems and implementation of appropriate management strategies requires accurate and well classified information describing supply, demand, and consumption. The WA + water accounting framework is a relevant tool in this regard. Earlier applications of the WA + framework draw heavily from remote sensing (RS) data; however, applying RS data limits the application of the framework to past and current situations. Such analyses are needed for future assessments due to new management and climate scenarios. Therefore, the objective of this research is to link WA + with the Soil Water Assessment Tool (SWAT) model to enhance it and to evaluate water management strategies through an integrated framework. The resulting system, SWAT-FARS (customized version of SWAT model for Fars region) is capable of supporting macro and micro water planning through a systematic presentation of the past trends, current and future status in water supply and demand. To explore this methodology, the system was applied to the Tashk-Bakhtegan basin (Iran). The trends in supply and consumption within the basin and some of the water saving policies that are mandated by the country's 6th development plan were evaluated. Application of SWAT-FARS to the Task-Bakhtegan basin showed decrease in "Manageable water" of about 23% and a simultaneous increase of "Incremental irrigation" of about 53%; this lack of accessible water and imbalance of manageable water and water usage has almost omitted the basin's "Outflows". To alleviate pressures on the basin's water resources, a suggested elimination of rice cultivation and improving pressurized irrigation showed the first policy could reduce water consumption by 0.08 BCM/yr and the second one can even increase water consumption by 0.25 BCM/yr over current conditions. The methodology used to develop SWAT-FARS is strongly recommended for other regions suffering water scarcity.