Is there a relationship between atmospheric rivers (ARs) and deadly floods? And are there meteorological phenomena that cause rainfall and flooding?
This work presents a new Performance-Based Atmospheric River Risk Analysis (PARRA) framework that adapts existing concepts from probabilistic risk analysis and performance-based engineering for application to AR-based river flooding. The PARRA framework is a chain of physically based models that contract atmospheric forcings, hydrological forcings, and economic consequences of AR-based riverine flood risk together at fixed "close points". Organizing around these pinch points makes the framework modular, meaning that models between pinch points can be updated without affecting the rest of the model chain, creating probabilistic output that determines the uncertainty in the underlying system states. The PARRA framework can generate results beyond the analysis of individual scenario events and can look at the prospective assessment of events or systemic changes not seen in the historical record.
Atmospheric rivers (ARs) are long (>2000 km) and narrow (500–1000 km) corridors with strong horizontal water vapor transport, with water mainly concentrated in the lowest 3 km of the atmosphere (Ralph et al., 2018). ARs are the main transporter for moisture transport from the tropics to the midlatitudes, accounting for up to 90% of the longitudinal water transport while covering only 10% of the land surface (Zhu and Newell, 1998). .ARs (atmospheric rivers) are critical to the sustainability of California's water resources: they can store up to half of the state's annual water in just one hundred hours of rain per year (Lamjiri et al., 2018). However, this gift comes at a price. ARs cause more than three-quarters of all extreme precipitation events in California and more than 90% of the state's recorded floods (Lamjiri et al., 2018), resulting in approximately $660 million in average annual damages (Corringham et al., 2019). One of AR's most devastating events was the Great Flood of 1862. Central California received over 3 meters of rain in 43 days between December 1861 and January 1862, and cities from San Francisco to San Diego set rainfall records based on the disaster that still stand today.
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