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Experts at Assembly hearing warn Californiafaces rapidly rising flood risk from stronger storms
Summary
Researchers told the California State Assembly at an informational hearing that flooding risk across the state is increasing because of climate-driven intensification of atmospheric rivers, current flood planning relies on past hydrology, and federal partners and funding are increasingly unreliable.
California faces a growing and urgent flood risk driven by stronger storms and rising atmospheric moisture, a panel of water experts told a State Assembly informational hearing on flooding.
Jeffrey Mount, a senior fellow at the Public Policy Institute of California, told the Assembly that climate projections indicate more intense atmospheric rivers, increasing the probability of very large floods. "The great flood of 1861-62 . . . may now be our hundred year flood," Mount said, summarizing recent modeling that shifts what had been considered very rare events into far higher frequencies.
Mount said flood risk is a function of event probability and economic exposure and that both are rising. He cited estimates of multi-billion-dollar annual damages even in relatively mild recent years and repeated projections that an extreme statewide flood could cause on the order of a trillion dollars in economic losses. "We're planning for the past. We're not planning for the present, and we sure as heck are not planning for the future," Mount said.
Why this matters: Flooding threatens lives, homes, infrastructure and the state economy. Assembly members were told that much of California's built environment sits on flood plains and that social inequities mean lower-income communities are often least able to recover after floods.
Key evidence and analysis
- Mount described four distinct flood modes relevant to California: fluvial (riverine) flooding, pluvial (rainfall-driven) urban flooding, debris flows (rapid water-and-sediment flows that can be lethal) and coastal flooding from storm surge and sea-level rise. He said pluvial and debris-flow damages are major contributors to overall losses.
- He stressed that federal flood mapping and the National Flood Insurance Program are largely calibrated to historical hydrology and thus understate current and future risk. "All the federal government calculates the so-called hundred year flood is all based on the hydrology of the past," Mount said.
- Mount warned of an "unreliable federal partner" on some flood-management fronts: forecasting and some federal program functions are being reduced, and federal capital investment has been constrained. He said some federal modeling centers have been downsized and that sustained federal technical capacity is necessary.
- On opportunities Mount and others raised groundwater recharge and aquifer storage as important climate-adaptation tools, but he cautioned that during extremely large storm events the volume that can be diverted to recharge is modest compared with peak flood flows.
Discussion and follow-up directions
Assembly members asked about the practical limits of aquifer recharge during high flows and about where to prioritize investments. Mount and colleagues urged updated statewide planning, more stable funding for flood management, better alignment of land use with flood risk, and a modernized approach to flood mapping that accounts for a nonstationary climate.
Ending
Mount concluded that while the outlook is sobering, improved forecasting, planning and investment can reduce social and economic impacts. He urged the Assembly to treat flood planning as anticipatory policy rather than a response driven by memory of the last disaster.
