California Senate Bill SB599

California 2025-2026 Regular Session

• Introduced: 9/10/25
• Introduced: 2/20/25
• Refer: 3/5/25
• Refer: 3/24/25
• Refer: 4/2/25
• Report Pass: 4/23/25
• Refer: 4/24/25
• Report Pass: 5/23/25
• Engrossed: 5/29/25
• Refer: 6/5/25
• Report Pass: 7/1/25
• Refer: 7/1/25
• Report Pass: 8/29/25

Caption

An act to amend Section 347 of the Water Code, relating to atmospheric rivers.

Summary

SB 599 would amend Section 347 of the Water Code to expand California’s Atmospheric Rivers Research and Forecast Improvement Program (AR/FIRO) within the Department of Water Resources (DWR). The bill requires DWR, when researching, developing, and implementing novel forecasting methods, to include experimental tools that produce seasonal and subseasonal atmospheric river forecasts. It also retains and reinforces DWR’s existing responsibilities to improve reservoir operations, flood protection, and water capture from atmospheric river events. The bill’s findings emphasize that atmospheric rivers are a major source of California’s precipitation and flood damage, and that climate change is making these events more intense and frequent. It cites recent flood disasters, aging flood infrastructure, and the potential benefits of better lead time for emergency planning, groundwater recharge, and water supply reliability. The bill defines “seasonal forecast” as roughly one to six months ahead and “subseasonal forecast” as roughly two to six weeks ahead.

Impact

SB 599 would not create a new program, but it would modify the existing AR/FIRO program by explicitly directing DWR to use experimental seasonal and subseasonal forecasting tools as part of its atmospheric river research and forecasting work. In practice, this would shape how DWR develops forecasting methods and uses forecast information in reservoir operations, flood control, and water storage decisions. The bill also requires that information generated by the program be shared with relevant federal, state, and local agencies. Because the bill is keyed to DWR’s research and operational functions, its main legal effect is on state water management policy rather than on private parties or local land use rules.

Sentiment

The overall sentiment around the bill appears strongly positive and noncontroversial. The recorded votes were unanimous at each stage shown, including committee votes and floor action, and the bill advanced with consent-calendar treatment. The context suggests broad agreement that improving atmospheric river forecasting is a practical flood-risk and water-supply strategy for California.

Contention

There is little evidence of substantive opposition in the available record. The main policy emphasis is on whether DWR should be specifically required to incorporate experimental seasonal and subseasonal forecast tools, but the bill’s language frames this as a technical enhancement to existing work rather than a major policy shift. The only notable procedural issue is that the bill was placed on the suspense file in committee and later moved forward, indicating fiscal review rather than disagreement over the underlying concept.