Intensified Atmospheric Rivers Set to Boost California's Water Reserves and Enhance Flooding Risks
California is witnessing a significant transformation in its precipitation patterns, with Atmospheric Rivers (ARs) playing an increasingly crucial role. A new study led by the University of California, San Diego, and co-authored by experts from various institutions, has found that the state's rainfall is becoming less frequent but more intense, posing challenges for water management and infrastructure.
The study, titled "Precipitation regime change in Western North America: The role of Atmospheric Rivers," reveals that the heavy precipitation in the West will come more prominently from ARs. All 16 global climate models project that California will receive more precipitation in a progressively more dramatic fashion due to climate change.
Alexander Gershunov, a climate scientist at Scripps, is the lead author of the study. He states that as Mediterranean climate regions around the world are becoming more subtropical, the dry season is expanding, and California is no exception. Gershunov also suggests that the heavy precipitation in California is projected to become more extreme.
The study found that the frequency of precipitation not related to ARs will diminish in California. This means that fewer overall storm events are expected, but when they do occur, they will be of greater intensity. In Southern California, studies forecast these high-intensity storms will produce greater volumes of stormwater runoff and pose challenges to existing stormwater infrastructure designed for lower peak flows.
The increased intensity of ARs, combined with California's topography, could result in the state receiving more precipitation on balance. However, the study also highlights that regional drought remains a concern alongside intense rainfall. For instance, while some areas experience heavy AR-driven precipitation, parts of Southern California continue to suffer from drought conditions.
The implications for water management are significant. The increased forecast accuracy of AR events allows water managers to better prepare reservoirs and flood control systems. With longer lead times, dam operators can optimize release schedules to mitigate flooding while preserving water supplies ahead of AR storms.
However, intensified storms will stress urban stormwater systems, leading to heightened risks of flash flooding, mudslides (especially in areas recently burned by wildfires), and water quality degradation due to overwhelmed drainage systems and impervious surfaces.
The study suggests that a new regime of wet and dry extremes is emerging in California. To adapt, water management must improve forecasting, expand storage capacity, modernise stormwater infrastructure, and integrate flood and drought risk management to handle this higher variability and risk profile.
The study was funded by the federal Bureau of Reclamation, the Southwest Climate Adaptation Science Center, NOAA, the U.S. Geological Survey, and NASA. The Center for Western Weather and Water Extremes at Scripps is leading projects to enhance the skill of AR forecasting. Improvements in the understanding and prediction of ARs could be a key tool in California's climate adaptation toolbox, potentially enabling the needs of 165,000 more people in one Southern California county to be met.
The study also highlights the success of the improved AR forecasting in practice. The improved skill of AR forecasting has been shown to improve water supply reliability and flood risk mitigation, as demonstrated on Lake Mendocino in collaboration with Sonoma Water and the US Army Corps of Engineers.
In conclusion, California's precipitation pattern under climate change and AR influence is trending towards less frequent but more severe storms that bring episodic heavy rainfall with significant flood risk, especially when soils are wet. Adapting to these changes will require a concerted effort from water managers, scientists, and policymakers to ensure the state's resilience in the face of a changing climate.
- The study revealing changes in California's precipitation patterns points towards a future where heavy precipitation events, predominantly from Atmospheric Rivers (ARs), will become more frequent due to climate change – a situation that could potentially impact the state's health-and-wellness and mental-health, as severe storms might lead to flooding and other environmental hazards.
- The increased intensity of ARs and changing precipitation patterns in California pose challenges not only for the state's environment (climate-change) but also for the infrastructure and management of its water resources, emphasizing the importance of improving scientific knowledge (environmental-science) and tools in forecasting and adapting to extreme weather events.
