Water planners are increasingly in need of raising more complete information on the hydrological and economic consequences of water management in order to take adequate decisions to secure water supply in the future. This paper combines a scenario-based modeling of future impacts on water availability at basin level with economic valuation to answer the following questions: Which is the most cost-effective adaptation strategy? Is adaptation bringing net benefits to society as opposed to no adaptation? How to select an efficient adaptation level, if any, when facing uncertainty on which future scenario will apply? The model integrates cost-effectiveness analysis of adaptation measures, monetary valuation of avoided scarcity impacts and hydrologic modeling. By testing a set of cost-effective strategies at basin level in several potential short-term drought scenarios, we identify the most efficient strategy that should be implemented by water planners. The model is applied to the Llobregat river, in north-east Spain