A Continuous Drought Risk Monitoring System, CDRMS, Based on Copulas

From the drought indices, the Standardized Precipitation Index, SPI, is the most used one. However, it is difficult to use to monitor the ongoing drought characteristics because it cannot be expeditiously related to precipitation deficits. It also does not provide information regarding the drought risk nor the temporal evolution of the droughts. By using the SPI, a copula-based Continuous Drought Risk Monitoring System, CDRMS, was developed aiming to monitor the droughts, including the risk of having a drought event as the rainy season advances. In climates with very pronounced rainy seasons, the absence of precipitation along the same is the fundamental booster of droughts. After presenting the CDRMS, the paper describes its application to Mainland Portugal, which showed that the system has an increased capability of anticipating the drought risk by the end of the rainy season as new precipitation records are known. The good performance of the system results from the ability of the copula to model complex dependence structures as those existing between precipitations in different time intervals. CDRMS is an innovative and user-friendly tool to monitor the precipitation and, consequently, the drought risk, allowing to anticipate mitigation and adaptation measures or even to issue alarms.