Research papersDrought early warning based on optimal risk forecasts in regulated river systems: Application to the Jucar River Basin (Spain)

•Modelling the past to anticipate future drought is an ineffective and risky approach.•A new method for continuous drought monitoring and early warning in regulated catchments is proposed.•Reservoir storage probability is a reliable indicator for drought status in regulated catchments.•New approach adds value to existing monitoring and early warning methods.

Droughts are a major threat to water resources systems management. Timely anticipation results crucial to defining strategies and measures to minimise their effects. Water managers make use of monitoring systems in order to characterise and assess drought risk by means of indices and indicators. However, there are few systems currently in operation that are capable of providing early warning with regard to the occurrence of a drought episode. This paper proposes a novel methodology to support and complement drought monitoring and early warning in regulated water resources systems. It is based in the combined use of two models, a water resources optimization model and a stochastic streamflow generation model, to generate a series of results that allow evaluating the future state of the system. The results for the period 1998-2009 in the Jucar River Basin (Spain) show that accounting for scenario change risk can be beneficial for basin managers by providing them with information on the current and future drought situation at any given moment. Our results show that the combination of scenario change probabilities with the current drought monitoring system can represent a major advance towards improved drought management in the future, and add a significant value to the existing national State Index (SI) approach for early warning purposes.