Assessment of Water Resources System in Zayandehrood Basin, Using Water Accounting Method Najmeh Mohammadi Khozani Najmeh.mohammadi@cv.iut.ac.ir Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc Language: Farsi Supervisor: Dr. Azadeh Ahmadi, aahmadi@cc.iut.ac.ir To cope with thegrowing challenges such as supply, distribution and management of water resources, especially in arid and semi-arid basins, it is necessary to use new approaches to manage water consumption and resources. One of these approaches to achieve a comprehensive understanding of the conditions of the basin, which has also been evaluated and used in this study, is System of Environmental-Economic Accounting for Water (SEEA-W) that introduced by the United Nations, which has been investigated in this study. Initially, the information required to complete the relevant tables in this method of accounting was examined. After understanding the information needed to complete the tables and realizing that the information available in the agricultural sector will increase uncertainty, the SWAT model simulation has been used to extract the information required by this section in the tables. For this, the Zayandehrood basin was simulated in 1988 to 2015 period. After basin simulation, runoff, evapotrairation and performance of dominant crops in the region were calibrated using the SUFI-2 algorithm in SWAT-CUP software for the years 1991 to 2009. The validation was taken for the years 2010 to 2015. In order to able the model to identify the basin conditions, the first three years of the simulation were considered as Warm up period. After validation, the extracted data from 2011 were used to complete the accounting tables in the agricultural sector using SWAT outputs. These tables show a water cycle for each user and the equilibrium and water exchange equation between the range of activities and the environment. In order to complete the physical tables of consumption and supply in other sectors due to the size of the area and the importance of the role of industry in it, the need for field research from relevant experts, especially in collecting information on water supply and wastewater and sewerage. After completing the physical tables using the results of the SWAT model in all fields of activities, the economic tables of the basin for 2011 were completed and indexes such as renewable water resources, dependence on groundwater resources and economic productivity, in each section for this this year was calculated. The economic productivity index, which shows the gross income of each sector divided by water consumption, was estimated at 23.401 Rials per thousand cubic meters in agriculture, 3092.8 Rials per thousand cubic meters in industries, and 1041.1 Rials per thousand cubic meters in urban drinking water and services. Industries have the highest economic productivity in the region due to the amount of water consumed (about 6%). Finally, to evaluate the basin in the agricultural sector as the biggest water consumer sector in the basin, agricultural and economic productivity indexes were examined. For 2011 in the whole basin, evapotrairation productivity index, 0.76 kg/m3, irrigation efficiency and effective rainfall index, 0.63 kg/m3, net profit index based on evapotrairation, 1786 Rials per cubic meter and net profit index based on irrigation water and rainfall, 1501 Rials was obtained per cubic meter. Rice as the product with the lowest agricultural productivity (effective rainfall productivity and irrigation and evapotrairation productivity) and alfalfa as the product with the lowest economic productivity (net profit to rainfall productivity Irrigation and the ratio of net profit to evapotrairation productivity were identified. Then, in order to increase the agricultural and economic productivity of crops in the basin, four scenarios were defined