Widespread Increase in Atmospheric River Frequency and Impacts Over the 20th Century

American Geophysical Union (AGU) | December 11th, 2025

Atmospheric rivers (ARs) are long, narrow regions of atmospheric moisture transport that provide water resources to many regions, but can also cause hazards such as extre

Atmospheric rivers (ARs) are long, narrow regions of atmospheric moisture transport that provide water resources to many regions, but can also cause hazards such as extreme rainfall and moist heatwaves. Despite their importance, there is uncertainty about how the frequency and impacts of ARs may be changing with time. Our study extends the global record of AR activity back to 1940. We find that the frequency of ARs has increased broadly across the midlatitude regions, rather than shifting polewards as observed in recent decades. This increase in AR frequency leads to more rain and snow associated with these features in both the mid‐ and high‐latitudes. We also find that there is an increase in humid heatwaves associated with ARs over the same period

Winter melt trends portend widespread declines in snow water resources

Nature Portfolio (Springer Nature) | April 5th, 2021

In many mountainous regions, winter precipitation accumulates as snow that melts in the spring and summer, which provides water to one billion people globally. Climate wa

In many mountainous regions, winter precipitation accumulates as snow that melts in the spring and summer, which provides water to one billion people globally. Climate warming and earlier snowmelt compromise this natural water storage. Although snowpack trend analyses commonly focus on the snow water equivalent (SWE), we propose that trends in the accumulation season snowmelt serve as a critical indicator of hydrological change. Here we compare long-term changes in the snowmelt and SWE from snow monitoring stations in western North America and find 34% of stations exhibit increasing winter snowmelt trends (P < 0.05), a factor of three larger than the 11% showing SWE declines (P < 0.05). Snowmelt trends are highly sensitive to temperature and an underlying warming signal, whereas SWE trends are more sensitive to precipitation variability. Thus, continental-scale snow water resources are in steeper decline than inferred from SWE trends alone. More winter snowmelt will complicate future water resource planning and management.

Winter wet–dry weather patterns driving atmospheric rivers and Santa Ana winds provide evidence for increasing wildfire hazard in California

Climate Dynamics (Springer) | August 12th, 2022

Floods caused by atmospheric rivers and wildfires fanned by Santa Ana winds are common occurrences in California with devastating societal impacts. In this work

Floods caused by atmospheric rivers and wildfires fanned by Santa Ana winds are common occurrences in California with devastating societal impacts. In this work, we show that winter weather variability in California, including the occurrence of extreme and impactful events, is linked to four atmospheric circulation regimes over the North Pacific Ocean previously named and identified as the “NP4 modes”. These modes come in and out of phase with each other during the season, result- ing in distinct weather patterns that recur throughout the historical record. Some phase combinations favor atmospheric river landfalls and extreme daily or multi-day precipitation, while other phase combinations favor anomalously hot weather and drying Santa Ana wind conditions over Southern California. This historical perspective of atmospheric circulation and impacts over 70 years reveals that weather patterns are changing in a way that enhances wildfire hazard in California, while the frequency of weather patterns linked to historical floods is not diminishing. These changes highlight the rising hazards of cascading weather extremes in California’s present and future.

Wright et al v. Goleta Water District

Superior Court of California, County of Santa Barbara | November 17th, 1989

Yuba Subbasins Water Management Plan: A Groundwater Sustainability Plan

Yuba Water Agency | December 27th, 2019

Yuba-Feather FIRO Final Viability Assessment

California Department of Water Resources (DWR) | March 14th, 2025

This Yuba-Feather Final Viability Assessment (FVA) evaluates whether improved precipitation and runoff forecasts can reduce flood risk downstream of New Bullards Bar (NBB

This Yuba-Feather Final Viability Assessment (FVA) evaluates whether improved precipitation and runoff forecasts can reduce flood risk downstream of New Bullards Bar (NBB), owned and operated by Yuba Water Agency (Yuba Water), and Lake Oroville (ORO), owned and operated by the California Department of Water Resources (DWR). These reservoirs are in the Yuba-Feather watersheds in the Sierra Nevada and eastern Sacramento Valley of Northern California (Figure ES-1 and ES-2). Each reservoirs’ flood risk reduction operations are regulated by United States Army Corps of Engineers (USACE) through Water Control Manuals (WCMs).  Reducing flood risk by making reservoir releases ahead of storms creates additional temporary flood storage space for anticipated inflows but requires confidence and skill in forecasted conditions.