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Are the California Wildfires a Sign of Climate Change?

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The exceptional heat in Southern California and the dangerous wildfires occurring since May 13 may be a sign of climate change given their severity and timing. As of Friday, May 16, over 10,000 acres have burned throughout Southern California and several locations have surpassed previous temperature records.

Image: National Weather Service

Image: National Weather Service

The role of the Santa Ana winds

One factor key to both the heat and wildfires ravaging Southern California is the role of the Santa Ana winds. The Santa Ana is defined as strong, extremely dry winds in southwestern California that blow westward through the canyons toward the coast. It is the product of strong high pressure over the Great Basin and lower pressure along the coast. Usually it occurs during the fall and winter and tends to produce the warmest temperatures of the year.

The Santa Ana winds season is projected to expand into the dry season in the presence of climate change. This could mean more wildfires coupled with heat waves like those we are seeing now. However, the underlying mechanism of Santa Anas, which require the gradient caused by cooler desert temperatures in the high pressure system over the Great Basin and lower pressures in the warmer coastal areas might weaken as the land warms faster than the ocean as the planet continues to get warmer. Thus, Santa Anas may occur less often during the season as the difference in temperature between the land and the ocean grows.

Impact from California drought

While droughts naturally occur, the current, devastating drought in California is a bellwether of what we can expect to occur more often if current greenhouse emission rates are not reduced. Recent research shows that the prevalence and duration of droughts have increased in the last 100 years.

The progression of the California drought of 2014 has had an impact on the available fuel for the wildfires. Already this year, the 1400 wildfires starting in January is more than twice the amount that usually occurs, according to Cal Fire. Most of the state is in “extreme drought,” with 25 percent of California experiencing “exceptional drought” conditions. The California wet season spans the October-April period. Only 51 percent of average rainy season precipitation fell during this period. Compounding this impact is the statewide snowpack water content, which is at 18 percent of its normal level.

Droughts can be made worse by climate change because warmer air induces more evaporation, effectively desiccating the land. Longer-term droughts such as the one in California or Australia also create a dangerous feedback loop that makes heat waves more likely and more severe. A recent study, published in Nature, proposes that dry soil becomes even drier with initial heat and pumps more heat to the air above, sustaining higher temperatures for longer.

Trends in temperature extremes

The National Climate Assessment indicates that extreme heat has shown the biggest trend over the Southwestern U.S. Heat waves in the state of California since the year 2000 have shown clear upward trends for interior regions and along the coast.  The clearest sign in these trends is the nighttime temperatures, which have risen, in unison, for a great majority of station observations throughout California.

Lowest daily temperature for the month of May for 1900-2010. Based on USHCN station observations with continuous, validated data for Pasadena, Paso Robles, Riverside, Santa Barbara, Ojai, San Bernardino.

Lowest daily temperature for the month of May for 1900-2010. Based on USHCN station observations with continuous, validated data for Pasadena, Paso Robles, Riverside, Santa Barbara, Ojai, San Bernardino.

The great heat waves of 2003 and 2006 were cataloged as “nighttime heat waves” in recent research. During these events, low temperatures were much warmer than average and unprecedented compared to previous events in the observational record. This is a dangerous component of the trends because it does not allow for a person to cool off after the heat of the day, putting many people without access to air conditioning in danger.

Just last year, a heat wave that started at the end of June broke multiple records across the Southwest U.S., making it the warmest day of any June in station observations. Heat extremes are also becoming more prevalent earlier in the year, as exemplified by May 2014 and in 2008. The extreme heat of May 2014 is doing the same for numerous locations in Southern California. The San Diego high temperature average is 68°F and it registered 97°F May 15 and this is the seventh record in the city this month alone. It also set a record high minimum temperature for the day at 70°F.

Climate change has played an important role in the lengthening of the wildfire season and this trend will continue in the future. A Cal Fire spokesman put it quite simple for the LA Times: the 2013 fire season rolled right into 2014.

Posted in: Global Warming Tags: , ,

About the author: Roberto Mera is a climate scientist and Kendall Science Fellow in climate attribution. His work entails analyzing specific carbon emissions to determine how they are affecting global temperatures and extreme heat events. He holds a Ph.D. in marine, earth and atmospheric science from North Carolina State. See Roberto’s full bio.

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  • Sherry M.

    I live in the foothill canyons of Orange County within the congressional boundary of the Cleveland National Forest. I have lived here for almost 40 years, almost 30 in the same home.

    I am an avid outdoors person and birder. This season, wildlife is just devastated by the drought. I would guess, based on several years of birding the exact same areas, some species are missing altogether and some are reduced by 90%.

    A recent front page article in the Orange County Register [Sun. May 18 edition] cites raptor experts Pete Bloom, Ph.D., and Scott Thomas on the conditions of raptor nests they have been watching for years. The drought has pretty much devastated an entire generation of raptors. They aren’t producing and the reason is pretty obvious; less prey because there is less rain, which causes low seed production.

    I feel like I am watching a world in a frying pan and until and unless we do something on a national level that is significant, it will get worse and be a problem longer.

    It is heartbreaking to watch the results on the natural world caused by both our actions and inaction. I am 61 and won’t see the worst of this, but know it is coming fast.

    Thanks for all the information you provide.

    • http://www.ucsusa.org/about/staff/staff/robreto-mera.html Roberto Mera

      Sherry,

      Thank you for your comment. It’s always interesting to hear the first-hand observations of those affected by climate change. It puts a human touch on the effects.

  • http://co2freefuelexistsnow.wordpress.com/ mike gilliland

    Convincing research! Congrats to Mr Mera, I’d like to comment really on the ‘GET MORE MILES TO THE GALLON’ article on the main site.
    When oh WHEN will UCS comission a study on NH3 fuel, which is CO2-free and toxic emissions free when burnt, nearly as energetic as gasoline, and can now easily be manuifactured from just air, water, some catalysts and electricity, preferably renewable.
    I just put ‘NH3 fuel’ in the UCS Search Engine and got NO RESULTS.. what is this? Another example of bought out science in the USA? Even Toyota proved NH3 works last year and Sth Korea is considering mass vehicle conversions, all internal combustion engines could be converted to run on NH3.
    Please UCS.. less emphasis on slightly modifying your collosal carbon footprint and more courage to examine real alternatives.
    see the full NH3 ‘green gas’ story here: http://co2freefuelexistsnow.wordpress.com/

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