Beginning on December 26, the West Coast was affected by a series of tropical cyclones causing heavy rains, overflowing rivers, flash flooding, levee breaches, mudslides, and more, along with some wind damage. .
The rainfall intensity in California was so extreme that several places in the central part of the state set three-week rainfall records, with some places receiving their average annual rainfall totals in less than a month.
Damage to infrastructure in the state was extensive. A combination of flooding and mudslides damaged state and local highways, and trees were uprooted by high water speeds, saturated soil, and high winds, which also damaged power grids, cars, and property. Moody’s RMS said.
Continued rainfall and impacts from riparian-groundwater-coastal interactions also caused prolonged flooding in some urban coastal areas.
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The cyclones hit California after a prolonged drought. 2022 was the second driest year in more than 128 years for certain areas of the state and was classified as “extreme drought” according to the National Drought Information System.
Even with flooding, California is unlikely to be out of the drought, especially when it comes to aquifer replenishment, Moody’s RMS said. High-intensity rainfall from the storms resulted in a high proportion of rainfall running off into the ocean, while aquifers are generally gradually recharged with less intense rainfall and snowmelt.
Insurance is expected to cover a relatively small proportion of the economic impact, Moody’s RMS said. The proportion of California households with flood insurance is less than 2% and has been steadily declining. As of August 2022, there were only 193,281 residential NFIP policies in force in the state, a decrease of about 5% from 2021.
“Extreme drought leads to soil compaction, which means less infiltration and more runoff, therefore less aquifer recharge and increased risk of flooding,” said Firas Saleh, director of product management at Moody’s RMS. “No place is safe from flooding in California today. If we have learned anything from this extreme rainfall and subsequent damage, it is that even flood zones perceived as low risk are still flood zones. If it rains, it can overflow.”
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