In changing climate, handling of uncertainty plays a prominent role in water resources assessment and management. To address the uncertainty in water management under climate change, the EU-funded project "Water Efficient Allocation in a Central Asian Transboundary River Basin (WE-ACT)" proposes a solution framework compromising five dimensions: data, climate model, impact model, scenario and communication.First, the scarcity of hydrometeorological stations and restricted data sharing, lead to uncertainty in impact assessments. To tackle the issues, WE-ACT establishes real-time hydrometeorological stations to improve data availability and adopts a hybrid cloud architecture database to enhance the technical foundation for transboundary data sharing.

Second, to reduce uncertainty from coarse resolution climate models and the propagation into the impact models, WE-ACT employs an ensemble of highly resolved regional climate models to account for abrupt elevation changes in Central Asia, enabling coupling with impact models to reflect the feedback of irrigation on local hydroclimatology.

Third, it is often difficult for a single impact model to capture all the processes associated with water allocation. WE-ACT uses an integrated modeling system, including water availability, water use, water footprint, and water allocation, to embrace uncertainty and compensate for one another's inadequate description of the processes.

Fourth, while the above options reduce uncertainty in climate impact assessment in water resources, uncertainty in management remains. WE-ACT follows the precautionary principle to develop management scenarios to cope with uncertainty in impact assessments. Examples include various water allocation scenarios under extreme prolonged severe drought conditions.

Finally, we engage stakeholders to understand their capacity and preferences for uncertainty and risk in decision making. Technically, a decision support system tool is also envisioned to communicate uncertainty and chart adaptive pathways toward alternative futures.

Although unknown unknowns remain under climate change, the WE-ACT solution serves as a compelling example of how water resources management can address uncertainty under climate change.