Atmospheric rivers: research: forecasting methods: experimental tools.

Senator Caballero's atmospheric river forecasting legislation expands California's water management capabilities by requiring the Department of Water Resources to incorporate experimental seasonal and subseasonal forecasting tools into its existing research program. The bill adds these longer-range prediction requirements to the department's Atmospheric Rivers Research and Forecast Improvement Program, which develops methods to anticipate and respond to these concentrated bands of Pacific moisture that deliver up to half of California's annual precipitation.

The legislation directs the department to apply these extended forecasts, ranging from two weeks to six months, to reservoir operations and flood control decisions. Under the bill, information from these experimental forecasting tools must be shared with federal, state and local agencies to support coordinated water management. The department would continue using forecast data to adjust reservoir operations for capturing atmospheric river flows while maintaining flood protection capacity.

This measure builds upon California's current atmospheric river monitoring system, which the bill's findings indicate has already demonstrated improved accuracy. According to the legislative findings, five-day forecasts in 2020 achieved greater precision than four-day predictions from 2017. The findings also note that atmospheric rivers have caused 94 percent of California's flood damages, averaging $620 million annually, while recent winter storms in 2022-2023 resulted in $30 billion in damages across 40 counties.