Future Climate Scenarios in California Signal Increased Volatility with Atmospheric Rivers Playing a Prominent Part
California, a state known for its diverse landscapes and climate, is experiencing a significant shift in its precipitation patterns, leading to increased volatility in water resources. This development is primarily due to the intensification of atmospheric rivers (ARs), as revealed by two recently published studies.
Atmospheric rivers deliver vast amounts of moisture, driving intense precipitation events as they make landfall, particularly in California. Alexander Gershunov, a research meteorologist at the University of California San Diego, led one of the studies published in the journal Geophysical Research Letters (GRL). He and his team analysed 70 years of historical vapor transport and precipitation data to create a catalog of AR behaviour along the West Coast of North America.
The intensification of ARs leads to more extreme precipitation events, causing both heavy rainfall and flooding but also contributing to variable water resource challenges including drought and landslides. In December 2022–January 2023, nine consecutive AR events in California caused catastrophic flooding and over 600 landslides, illustrating how AR intensification raises the risk of extreme localized precipitation impacts.
However, California continues to experience severe drought conditions, with over 93% of the western US in drought and significant dry conditions persisting. This shows that intense AR-produced rain is episodic and often insufficient to alleviate long-term water deficits aggravated by climate patterns such as the negative phase of the Pacific Decadal Oscillation (PDO) and human-induced warming.
The interplay between AR-driven heavy precipitation and persistent drought leads to challenges in water management, including reservoir management, flood control, and wildfire risk due to dry spells followed by intense rainfall affecting vegetation fuel moisture.
The second paper, published in Scientific Reports, predicts that Mediterranean climate regions, including California, will become drier due to the expanding subtropical belt and less frequent precipitation. Long dry periods between storms allow more time for toxins and pollutants to accumulate on the land surface, increasing the amount of toxic runoff going into the ocean and affecting coastal ecosystems and human health.
It is important to note that this work was funded by the Department of the Interior via the Southwest Climate Science Center and the U.S. Bureau of Reclamation, the California Department of Water Resources, and NOAA's California and Nevada Applications Program.
In summary, the intensification of atmospheric rivers causes more extreme precipitation patterns—floods and heavy rains—yet does not fully mitigate long-term drought stress on California’s water resources, instead complicating water availability and hazard risks due to the episodic nature of ARs combined with ongoing climate trends in the region. This volatility leads to more variability in water resources from year to year, making droughts and floods more likely.
Climate science research, as presented in a study led by Alexander Gershunov of the University of California San Diego, has revealed that the intensification of atmospheric rivers (ARs) is causing significant shifts in California's precipitation patterns, contributing to both heavy rainfall and flooding, as well as exacerbating existing water resource challenges such as drought and landslides.
Moreover, another study published in Scientific Reports predicts that Mediterranean climate regions, including California, will become drier due to the expanding subtropical belt, which increases the amount of toxic runoff going into the ocean and affects coastal ecosystems and human health, further complicating the management of water resources in the region.
