A practical approach for understanding and monitoring the sustainability of a river basin as a complex socio-hydrological system is to co-develop an indicator-based assessment framework with the help of the major stakeholders. This study defines the concept of Sustainability Assessment (SA) in the context of water management at basin level. A step-by-step methodology is proposed and further applied for developing indicator-based SA framework in the complex and overexploited Mashhad Basin in Iran. The methodology is based on a participatory approach that includes forming an expert panel of basin stakeholders, co-creating goals and objectives, identifying and screening indicators, and shaping the final SA framework. We identify 332 potential indicators from existing literature. Using selection criteria and two-round of fuzzy Delphi method, we adapt 25 fit-for-purpose indicators relevant to sustainable water management in Mashhad Basin. Subsequently, a SA framework is developed by categorizing final indicators into four main components (Technical, Environmental, Economic and Social) and ten subcomponents to provide better links and insights of the basin water management practices between different groups of stakeholders. Finally, using a weighting scheme through the Analytical Hierarchy Process (AHP), a sustainability index is constructed by aggregating the indicators. The results indicate that Mashhad Basin is in a critical unsustainable condition with a sustainability index at 0.34 out of 1. Analysis of the relative importance of the adapted indicators shows that the top-four ranked indicators (including water productivity, access to safe drinking water, renewable groundwater dependency and water pollution) have almost 40% contribution to the basin sustainability index. Such indicator-based SA framework can support identification and analysis of major sustainability trade-offs. Additionally, it can provide an effective tool for achieving water-related targets of the Sustainable Development Goals (SDGs). We therefore highly encourage further development of indicator-based SA frameworks in the context of water management at basin level.

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