Testimony: An Introduction to Flooding in California

PPIC Water Policy Center senior fellow Jeffrey Mount testified at the Assembly Water, Parks, and Wildlife Committee Information Hearing, "Is California Ready for Flood?" on March 11, 2025. Here are his prepared remarks.

Madame Chair and Honorable Members of the Select Committee,

Although California is best known for droughts and wildfires, the state is also prone to large, damaging floods. And the changing climate-including increasing storm intensity and rising sea level-is increasing the risk of flooding.

In my presentation to the committee, I will offer an overview of flood risk in California and illustrate some of the major challenges the state faces as flood risk continues to rise. The presentation will focus mostly on rainfall floods, but I want to remind the committee that the economic risks associated with coastal flooding are just as high.

The following points are essential to understanding flood risk in the state:

• Flood risk is high. Roughly one-in-five Californians are at risk of flooding and all 58 counties have had severe flood emergencies. Floods have the capacity to have more economic impact than wildfires or earthquakes, with a large statewide flood potentially leading to $1 trillion in damages.
• Flooding comes in many forms. There are four general types of floods: fluvial (overflow from rivers); pluvial (rainfall that exceeds urban drainage systems); debris flows (sediment-laden flows that often form below burned areas); and coastal flooding (high waves and tides).
• Structures are commonly used to mitigate floods. Thousands of miles of levees, hundreds of dams, bypasses, and flood retention basins are used-at great economic, social, and environmental cost-to manage floods.
• Non-structural flood control is also a vital tool. All major urban areas make use of hazard mitigation planning and land use zoning, with the latter largely reliant on federal flood hazard maps. Federally subsidized insurance and emergency response and recovery programs greatly reduce the social and economic impacts of floods.
• Climate change is increasing risk. The design and operation of flood infrastructure and the development of flood hazard maps all have a fundamental problem: they are based upon the climate of the past, not the present, and do not anticipate a future with growing storm intensity. By mid-century most urban flood control systems in California will not provide adequate protection.
• There are many obstacles to reform. Human nature, economic pressure to develop in flood-prone areas, and the difficulty of changing the institutions that manage floods make it hard to tackle increasing flood risk. But the most difficult hurdle may be financial, with an annual investment shortfall of $1 billion. Flood management is a "fiscal orphan" with no reliable source of revenue.
• Flood management relies heavily upon federal support. The federal government plays a role in all facets of flood management, not just financial support for infrastructure. Over the past few decades, federal investment in major infrastructure projects has declined. There is uncertainty over how reliable this support will be going forward.

I thank the committee for holding this hearing to highlight the importance of flood management in California. Flooding is the state's most pernicious natural hazard, but large, damaging floods are rare, making it difficult to make progress because the threat is not top of mind like wildfires and drought. And despite California's national leadership on climate issues, flood management remains not only a fiscal orphan, but a policy orphan as well, with major uncertainties over federal policies and support. I applaud the committee's efforts to bring this issue to the fore.