Probabilistic approach for drought mitigation measures in the Sardinian water systems

The risk management of water scarcity depends on the level of system drought state. An adequate diagnosis of the water scarcity level is essential to anticipate actions in terms of mitigation measures in a proactive approach. This diagnosis requires a definition, application and evaluation of a system of drought indicators to monitor and forecast drought events. This study proposes a methodology for drought risk management based on the evaluation of indicators of water scarcity to be used to define the thresholds of risk management actions. Indicators are a link between system state and proactive management actions. Arguing for the necessity of dynamic indicators relating supply and demands, in this paper the system state is expressed in terms of single or aggregated reservoir volume and it is related to vulnerability of demands. The methodology is based on the evaluation of the probability of not being able to satisfy system demands for a time horizon for a given system drought state. Sensitivity analysis of model parameters (reservoir volume, probability, demand vulnerability and time horizon) is presented. Based on thresholds of conditional probability value, 4 levels of drought severity are defined (no drought, pre-alert, alert and emergency) with recommended proactive measures. An extensive application of the methodology to the Flumendosa-Campidano water system located in South Sardinia (Italy) is presented. The huge complexity of this water system where severe droughts have occurred in the last 3 decades highlights the strengths and limitations of the proposed approach.