Large storms can overwhelm flood control channels and damage pipelines and other infrastructure. Rivers carry debris and sediment to reservoirs, where they can clog filtration systems, especially in burned areas. This was a concern in Fresno after the 2020 Creek Fire.
Storm surges and large volumes of rainfall can overwhelm unprepared city systems. An ARkStorm scenario, developed by the US Geological Survey, envisions a series of hurricane-level atmospheric rivers from the tropical Pacific slamming into the US West Coast over several weeks. Patterned after the Great Flood of 1861-1862, which put the Central Valley under as much as 15 feet of water, the ARkStorm scenario could flood thousands of square miles of urban and agricultural land, costing some $725 billion.