New paradigm in hydrologic risk: Importance of integrating consecutive events of dry and wet extremes for improved infrastructure resilience

Dry and wet extremes are often considered separately in hydrologic risk assessment and water resources management (e.g., dam operations) although they are the extremes of the same hydrologic cycle and can occur in close succession without leaving reasonable recovery time for critical infrastructure (e.g., dams, levees, dikes, or reservoirs). Ignoring this aspect can lead to the underestimation of hydrologic risk and challenge infrastructure resilience, as happened in Oroville dam in 2017, among others. Besides, if infrastructure is affected severely by one extreme (e.g., drought) cascading effects of the consecutive extreme (e.g., flood) can be devastating. We characterize consecutive dry and wet (CDW) extremes at global scale using the Standardized Precipitation-Evapotranspiration Index (SPEI) and estimate their compound risks. We find hotspots of CDW (frequency and severity) spread across North America, Europe, and Australia. Results indicate that the exceedance probabilities of the occurrence of dry and wet extremes are higher when CDW events and their associated dependence are considered compared to their independent and isolated counterpart. This reveals the importance of integrating CDW with appropriate dependence structure for quantifying hydrologic infrastructure risk. Furthermore, we investigated teleconnections between CDW and sea surface temperature (SST) and unveil that warm and cold phases of SST over the Nino3.4 region (5°N-5°S, 120°-170°W) can explain the frequency and severity of CDW at all global hotpots.