Assessment of changes in severity of compound drought and saltwater intrusion events based on a multi‐index approach in Pearl River estuary

Abstract Global warming alters the inherent variability of climate variables and induces more frequent extremes of hydroclimatic compound events with substantial impacts. The concurrence of hydrological drought and saltwater intrusion in the estuary can have devastating effects on agricultural production, water security, and ecological health. In this study, the compound drought and saltwater intrusion extreme indices, including the Blend Drought and Saltwater intrusion Index (BDSI), the Compound drought and Saltwater intrusion Index (CDSI) and the Standardized Drought and Saltwater intrusion Index (SDSI), were constructed to monitor compound extremes in the critical zone of Pearl River Estuary during the dry season from 1999 to 2016. The results reveal that the three compound indices can effectively depict different aspects of compound drought and saltwater intrusion extreme events in the critical zone of Pearl River Estuary. Among the three indices, the SDSI performed best in depicting compound drought‐saltwater intrusion events, while the BDSI outperformed the other indices in depicting high value of Standardized Runoff Index (SRI) and Standardized Saltwater intrusion Index (SSI), and the CDSI outperformed the other indices in depicting low values of SRI and SSI. Using those developed compound indices, we found that the frequency of abnormal and moderate compound drought‐saltwater intrusion events increased from 9.26% to 12.03% during the period of 1999–2016, while severe, extreme and exceptional compound drought‐saltwater intrusion events were rare.