The West Coast rainy season lasts from November to April. Seasonal rains can bring heavy flooding. There is also an increased flood risk as a result of weakened levees and land made vulnerable to mudflows from past wildfires.

Mudflows
A string of large wildfires have dramatically altered the landscape and ground conditions in several Western states. The charred ground in burned areas cannot absorb water easily, making residents especially vulnerable to flooding.

Mudflows and mudslides occur when fire-scorched earth saturates with rain and gushes down hills. Properties directly affected by fire, as well as those located below or downstream of the fire areas, are at the most risk, including properties that were previously not considered at high risk for flooding. Experts say that it may take years for the vegetation to return, and without this vegetation and ground cover, rainfall can cause the soil on the steep slopes to become powerful, devastating mudflows.

Levees and Flooding
The West Coast has thousands of miles of levees. These embankments along waterways, usually made of earth, are designed to protect lives and properties in the event of a flood. However, no levee provides full protection from flooding.

Levees can and do decay over time, and maintenance can become a serious challenge. Levees can be overtopped and even fail in large flood events, with catastrophic results. The flood damage after a levee failure can be more significant than if the levee was not there. For these reasons, people living near levees need to understand the flood risks they face. Local officials can provide more information about nearby levees and the related flood risk your property faces.