Modifying physical supply and use tables (PSUTs) in the system of environmental-economic accounting (SEEA) for off-farm irrigation water management

A reliable water accounting framework is crucial for understanding the contribution of water resources in meeting agricultural demands and selecting appropriate operating systems for off-farm water systems, including hydraulic conveyance and distribution structures. This ensures fair, adequate, and dependable irrigation water distribution, especially under water scarcity operational scenarios. This study presents a novel and effective method for modifying PSU tables in the SEEA water accounting framework that is specifically designed for smallscale agricultural water management study areas. The proposed approach entails a comprehensive analysis of the surface water distribution within the water holders using a hydraulic simulation model and a spatial analysis of the groundwater extraction for meeting on-farm water demands. This approach was implemented on Iran's Central Plateau and revealed notable variations in water rights and distribution effectiveness among stakeholders so that, surface water contributed 27-40% less than the legal water rights, leading to aquifer overexploitation. The evaluation indicated that changing crop patterns and upgrading to pressurized irrigation systems led to 4-7.5% overexploitation of groundwater and 3.5-6% water conservation on farm scales. Besides, the spatial assessment verified a considerable overlap of 59% between the farms with modern irrigation systems and those with cultivated area expansion, resulting in sustained overexploitation pressure on the aquifer. The present study has two significant practical implications. Firstly, it specifies the contribution of surface-and groundwater resources in fulfilling the water demands of individual water-holders. Secondly, it provides reliable information to decision-makers about the incentives for modernization, rehabilitation, and renovation projects in an irrigation district.