DWR Advances Groundbreaking Climate-Resilient Flood Mapping Through FEMA Partnership

Pioneering effort modernizes flood risk analysis in California’s Central Valley by integrating future climate scenarios, revealing a growing risk of flooding in the years ahead.

A groundbreaking flood mapping study completed by the California Department of Water Resources (DWR) shows that climate extremes will significantly increase major flooding in the coming decades, highlighting the urgent need for stronger state and regional flood management efforts to prepare for and address these rising risks and more frequent flood events.

Research has consistently shown that as the climate warms, the atmosphere holds more moisture — intensifying the strength and destructive potential of major atmospheric rivers reaching California. In response to the growing flood risk, DWR partnered with the Federal Emergency Management Agency (FEMA) under the Cooperating Technical Partners Program to complete a groundbreaking flood mapping study that represents a major advance in climate-resilient flood planning. By integrating future climate scenarios into flood inundation modeling, this innovative effort delivers more accurate information for communities, planners, and emergency managers. It equips them to better understand and prepare for the evolving risks of extreme flooding and can help target future state and local investments in flood infrastructure.

Focusing on the Tuolumne River area in Stanislaus County, the study aimed to demonstrate the value of a climate change-informed approach to flood risk. It provides planners and decision-makers with a clearer understanding of three critical questions: What are the potential flood scenarios? How likely are they to occur? And how severe could the impacts be?

To answer these questions, the study evaluated flood impacts across a range of possible future climate outcomes rather than relying solely on outdated historical data or just a few climate change projections. The study found that:

• By 2070, the largest floods on the Tuolumne River—the kind that currently have a 1 in 100 chance of happening in any given year—are expected to get much worse. These peak flows could double, and there’s a small (5%) chance they could grow nearly 3 times larger.
• By 2070, the floodplain will significantly extend beyond the boundaries shown on current FEMA 100-year flood maps, exposing both critical infrastructure and new areas at greater risk.

These climate projections highlight the uncertainty that flood planners and decision-makers must account for as they navigate the challenges of a changing climate. Studying and planning for these possibilities now will help ensure future flood infrastructure investments are targeted to where risk will be in the future rather than where it has been in the past.

“We know that historical assumptions no longer capture the full scope of flood risks in a changing climate,” said Romain Maendly, DWR Climate Action Coordinator. “This study shows how we can better prepare California’s communities by embracing science-based planning rooted in future conditions, not just past trends, and provide local entities with confidence to plan amid the uncertainty of our changing climate.”

In addition to technical innovation, this effort prioritized community engagement. Local agencies helped shape the development of the mapping tools, ensuring the results were not only scientifically sound but also locally relevant and easily understood. This emphasis on inclusive engagement aligns with recommendations in FEMA’s 2024 Climate Adaptation Planning Guide and supports DWR’s mission to strengthen equitable climate resilience across the state.

This study will inform the 2027 update of the Central Valley Flood Protection Plan (CVFPP) — focused on strengthening flood system climate resilience, providing a scalable, science-based approach for evaluating climate-driven flood risks across the Central Valley.

The study also aligns with DWR’s broader climate planning initiatives, including the State Water Project (SWP) Delivery Capability Report, upcoming SWP Adaptation Strategy, and the San Joaquin Watershed Studies. These initiatives share a common goal: to seamlessly incorporate climate science into California’s water management systems through a coordinated and integrated approach.

As the importance of climate-resilience grows, DWR’s early leadership positions the department as a model for other state and federal agencies.

Read the Case Study Report.

Read the Modeling and Inundation Study Report.