Revision of the Scarcity State Indicator in the Spanish Drought Management Plans

Droughts are one of the gravest natural threats currently existing in the world and their occurrence and intensity might be exacerbated due to Climate Change. Scarcity is defined as the period when demand does not accomplish the normal reliability levels due to poor water management. Water and drought management plans (DMP) prevent scarcity periods by anticipating to drought and adapting to limited water resources. DMP in Spain were updated in December 2018. Two types of indicators were included: The Prolonged Drought Indicator and the Scarcity State Indicator (SSI). This study presents a comparison of the SSI among seven river basins in Spain, with the aim of making a starting point for its optimization and computation. The scarcity indicator is based on the relationship between the availability of resources and demands, identifying situations of short-term deficit in each of the areas defined. Its computation consists of a seven-step iterative process. Results detect two different approaches when determining the threshold values for the SSI. One method bases the threshold estimation on the risk of supply of the demands while the other obtains the threshold values from direct statistics of historical variables. The authors thank the Spanish Research Agency (MINECO) for the financial support to ERAS project (CTM2016-77804-P, including EU-FEDER funds).