Climate patterns in California winters
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California Winter Climate Patterns: Temperature and Precipitation Trends
Warming Trends in California Winters
Over the past century, California winters have experienced significant warming, especially in minimum daily temperatures (Tmin), which have increased more than maximum daily temperatures (Tmax) Wang2017Bonfils2008Cordero2011. The average Tmin trend across California from 1920 to 2015 ranges from 1.2°C to 1.9°C per century, while Tmax trends are more variable, ranging from -0.3°C to 1.2°C per century . This warming is most pronounced in late winter and early spring, and is attributed to human-induced changes in large-scale atmospheric circulation rather than natural climate variability . Since 1970, the rate of warming has accelerated, with Tmin and Tmax both rising, particularly in the southern deserts during spring .
Precipitation Patterns and Variability
California’s winter precipitation is highly variable from year to year, with only about 25% of this variability linked to El Niño–Southern Oscillation (ENSO) events Jiang2022Seager2015. Most of the variability is due to circulation anomalies over the West Coast that are independent of ENSO, making seasonal prediction of winter precipitation challenging . Climate models project that, unlike other Mediterranean climate regions that are expected to dry, California may see wetter winters under global warming, primarily due to an eastward extension of the westerly jet stream over the North Pacific . This jet extension is mainly driven by uniform sea surface temperature (SST) warming, with El Niño-like SST patterns playing a secondary role .
Extreme Weather Events: Atmospheric Rivers, Floods, and Wildfires
California winters are marked by recurring extreme weather events, including floods from atmospheric rivers and wildfires fueled by Santa Ana winds Guirguis2021Guirguis2022. These events are linked to four main atmospheric circulation regimes over the North Pacific, known as the NP4 modes, which interact to produce distinct wet and dry weather patterns Guirguis2021Guirguis2022. Recent decades have seen changes in these patterns that increase wildfire risk, while the frequency of flood-linked weather patterns has not decreased Guirguis2021Guirguis2022. Compounding extremes—such as wet years followed by drought and wildfire—are becoming more common, raising the risk of cascading hazards Guirguis2021Guirguis2022.
Future Projections: Temperature and Precipitation Changes
Climate models consistently project significant warming across California by the 2060s, with the hottest historical July becoming only modestly warm in the future, and Januarys becoming notably warmer Pierce2013Cayan2008. While annual precipitation changes are small compared to natural variability, winters in northern California are expected to become modestly wetter, while spring and autumn may become drier Pierce2013Cayan2008. The most pronounced impact of warming is on snow accumulation, with substantial losses projected, especially in high-emission scenarios Wang2017Cayan2008.
Conclusion
California winters are becoming warmer, with minimum temperatures rising faster than maximum temperatures. Precipitation remains highly variable and difficult to predict, but future projections suggest a trend toward wetter winters, especially in the north, due to changes in atmospheric circulation. Extreme weather events, including floods and wildfires, are increasingly shaped by shifting weather patterns, raising the risk of compounding hazards. These evolving climate patterns underscore the need for improved prediction and adaptation strategies in California.
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Most relevant research papers on this topic
How much have California winters warmed over the last century?
California winters have warmed over the last century, with maximum temperatures increasing by 0.3 to 1.2°C/century and minimum temperatures increasing by 1.2 to 1.9°C/century, impacting snow water equivalent.
Weather Patterns Driving Atmospheric Rivers, Santa Ana Winds, Floods, and Wildfires During California Winters Provide Evidence for Increasing Fire Risk
California's winter weather patterns, driven by the "NP4 modes," are changing, enhancing wildfire risk and not diminishing flood frequency, highlighting the increasing hazards of compounding weather extremes in the state.
DOI
Winter wet–dry weather patterns driving atmospheric rivers and Santa Ana winds provide evidence for increasing wildfire hazard in California
Winter weather patterns in California are changing, enhancing wildfire hazard while not diminishing flood frequency, highlighting the increasing hazards of cascading weather extremes in the state.
Causes of the 2011–14 California Drought
SST forcing can explain up to a third of California winter precipitation variance, with La Nina events in 2011/12 and warm west-cool east tropical Pacific SST patterns in 2012/13 and 2013/14 contributing to the drought.
The identification of distinct patterns in California temperature trends
California temperature trends show distinct spatial and temporal patterns, with different rates of warming in minimum and maximum temperatures, suggesting a variety of different forcing mechanisms or feedback processes.
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