Can climate services help reconcile environmental flows and irrigation water allocation during drought?

Water allocation during drought often prioritizes short-term human demands over freshwater ecosystem needs. An important barrier to reconciling socio-economic and environmental water uses is the high uncertainty surrounding drought onset, evolution, and cessation. Climate services providing seasonal forecasts of water availability offer potential to reduce this uncertainty and support more proactive management. However, their use remains limited due to misalignment with decision-making practices and low user trust. This study engages with decision-makers in the Douro River Basin (Spain) to investigate how seasonal forecasts can minimize environmental flow restrictions during drought while avoiding unnecessary irrigation restrictions in the Órbigo catchment. Through co-creation with decision-makers we explore how seasonal forecasts could add value. We then assess this potential value through a seasonal forecasting modelling chain adapted to user preferences and simulating their decision processes, particularly in the trade-off between allocation to irrigation water use and environmental flows. Our results reveal that decision-makers are more interested in forecast probabilities relative to climatological decision thresholds (i.e. anomalies) than absolute forecast magnitudes, likely influenced by initially low trust in forecasts. Model results over a 40-year period (1981-2020) indicate that during most drought years, accurate forecasts enable maintaining environmental flows, particularly during drought recovery, and largely without compromising irrigation restrictions. In some years, accurate forecasts generated co-benefits by reducing both environmental and irrigation restrictions, while in others, inaccurate forecasts led to higher unnecessary irrigation restrictions, relative to current practices. This study demonstrates that climate services can, with proper stakeholder involvement, provide seasonal forecasts that enhance environmental flow management during drought, thereby reducing conflicts and supporting the objectives of the European Water Framework Directive.