An analysis released on Wednesday shows 2,933 properties were impacted by the early March flooding across California, with an average inundation depth at building level of just over 1 foot.
ICEYE’s Flood Insights, a data utility for insurers and emergency management organizations, uses radar imagery from satellites and ground-source data. The report shows the total flood extent of the event across California was 459.7125 square miles.
Data at the building level shows that 2,487 buildings in the flooded regions experienced inundation levels of up to 2 feet, with 390 buildings incurring flooding of between 2 to 5 feet; 44 buildings between 5 – 8 feet, and 12 buildings over 8 feet, according to ICEYE.
This analysis is focused on data specific to the regions most affected by the floods, including: Pajaro, Porterville, San Jose, Salinas, Visalia, Gilroy, Watsonville, Old River, San Joaqiun River, Sacramento River, Salinas River and the Sierra Foothills.
In early March, California experienced heavy snow followed by warmer atmospheric river storm systems, leading to a significant risk of flooding. Snow levels rose above 7 feet, and there was rapid snowmelt, increasing the risk of flooding across many locations.
Heavy rainfall measured 2-3 inches in several areas and up to 10 inches in localized regions. Flooding was observed near the coast north and south of the San Francisco Bay Area, and significant river flooding from heavy rain and snowmelt runoff along the Sierra Nevada foothills, according to ICEYE.
“Approximately one week before the flooding began, the ICEYE team was already monitoring the development of this large-scale meteorological event,” said Brandon Wright, a lead meteorologist at ICEYE.
Wright said his team was monitoring atmospheric rivers of tropical moisture systems, stretching for thousands of miles, which were on track to impact California. The region was already experiencing significant snowfall, with snow in the Sierra Nevada region near record levels.
“So, when the warm atmospheric rivers hit, they brought extensive heavy rainfall and triggered extremely rapid snowmelt, resulting in widespread flooding within a very short period,” he said.
Unlike rain-based flood events where there is often a delay between the weather system impacting and the floods commencing, the flooding in California was “almost instantaneous due to the accelerated snowmelt,” he explained.
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