Reports this week from the front lines of the Sand Fire in Southern California painted the scene as apocalyptic. The drought-fueled blaze was explosive, fast-moving and devastating, burning through 38,000 acres in the Santa Clarita Valley and forcing the evacuation of more than 10,000 homes.

If the state’s wildfire season holds true to forecasts, the Sand Fire will be one of many catastrophic wildfires to scorch drought-stricken forests and shrublands across California this year. So far, only one wildfire has been larger — the 48,019-acre Erskine Fire, which started in June in the Sierra Nevada Mountains and destroyed 250 homes and buildings.

None of the fires have been among the worst or largest wildfires the state has seen in recent years, but they’re part of a dire global warming-fueled trend toward larger, more frequent and intense wildfires. The number of blazes on public lands across the West has increased 500 percent since the late 1970s, said LeRoy Westerling, a professor studying climate and wildfire at the University of California-Merced.

The outlook this summer is sobering: Wildland fire potential for most of coastal California and the Sierra Nevada Mountains is above normal and is expected to remain that way through October, according to the National Interagency Fire Center.

The wildfire forecast follows a major heat wave in California, where the temperatures soared above 120°F (48.9°C) in some parts of Southern California. The region is seeing a significant warming trend. Each decade since 1970, average summer temperatures have warmed about 0.45°F (0.25°C).

The worst of the fire season in Southern California may be yet to come, said Hugh Safford, a U.S. Forest Service ecologist based in Vallejo.

“The most dangerous fire conditions occur from the end of September to December, when Santa Ana winds from the desert interact with the driest fuels of the season after five to six months of drying,” he said. “I would expect an active fire season, and critical conditions in the fall.”

Westerling said 140,000 acres have burned across Southern California this year — a figure that amounts to nearly four times the five-year average for annual acreage burned in an entire wildfire season in the region.

Global warming’s fingerprints can be clearly seen on this year’s fire season in California, where the state’s extreme drought is entering its fifth year and record-breaking heat has baked the region.

“Climate change has exacerbated naturally occurring droughts, and therefore fuel conditions,” said Robert Field, a research scientist at NASA’s Goddard Institute for Space Studies.

The worse the drought, the more of a tinderbox forests become.

“Higher temperatures exacerbate the drought by increasing evaporation and transpiration,” Westerling said. “Drier conditions mean highly flammable (wildfire) fuels. Drier conditions and high temperatures drive more extreme fire behavior.”

Southern California fire conditions today are already bad as firefighters attempt to contain the Sand Fire and battle the Soberanes Fire, which has burned more than 31,000 acres south of Monterey since the fire started on July 22.

The Sand Fire, burning in mountainous shrubland known as chaparral, has surprised wildfire scientists because of the speed with which it scorched the slopes north of Los Angeles. It’s an example of how climate change affects the way wildfires burn.

“Chaparral always burns at high intensity, but the mean size of chaparral fires has been growing,” Safford said. “We haven’t seen much change in the severity of these fires, but they are getting bigger on average, which may be due to drought-driven shrub mortality.”

Dead and dry trees do a lot to help fires spread, he said.

“This last factor results in fire embers that are cast far ahead of the flaming front and leads to faster fire growth and more difficult control,” Safford said.

Climate Central is an independent organization that researches and reports on climate change.

  • VooDude

    Doerr & Santín 2016 ”…many consider wildfire as an accelerating problem, with widely held perceptions both in the media and scientific papers of increasing fire occurrence, severity and resulting losses. However, important exceptions aside, the quantitative evidence available does not support these perceived overall trends. Instead, global area burned appears to have overall declined over past decades, and there is increasing evidence that there is less fire in the global landscape today than centuries ago.”

    ”Regarding fire severity, … little change overall, … area burned at high severity has, overall, declined…”

    ”Analysis of charcoal records in sediments [31] and isotope-ratio records in ice cores [32] suggest that global biomass burning during the past century has been lower than at any time in the past 2000 years.”

    ”The availability of satellite data now allows a more consistent evaluation of temporal patterns in area burned. Thus, from an analysis based on MODIS burned area maps between 1996 and 2012, Giglio et al. [35] present some rather notable outcomes. In contrast to what is widely perceived, the detected global area burned has actually decreased slightly over this period (by 1% per year). A more recent global analysis by van Lierop et al. [36], based primarily on nationally reported fire data supplemented by burned area estimates from satellite observations, shows an overall decline in global area burned of 2% per year for the period 2003 – 2012.”

    ”… the region used in Giglio et al.’s analysis excludes the boreal and drier southeastern zones of the USA, and (ii) area burned in the studies focused on the USA [42 – 46] is based on national and regional fire statistics produced using a variety of methods. These statistics need to be viewed with some caution when examining trends as annual reporting methods and biases have undergone changes over time [47]. Indeed, according to national statistics for the USA, while area burned by prescribed fire has changed little overall since reporting began in 1998 (10 year average: 8853 km^2), area burned by wildfires has seen an overall strong trend of increase by over 5% per yr over the period 1991 – 2015, with 2015 exceeding 40,000 km^2 burned for the first time during the past 25 years (figure 3).”

    ”… for the Californian Cascades and Sierra Nevada, Mallek et al. [49] suggest that ‘modern’ (1984 – 2009) annual area burned was only 14% of that burned annually prior to European settlement (approx. 1500–1850).”

    ”… the general perception of increasing fire around the world is not supported by the data available to date.”

    ”The notion that fire intensity and severity have increased in recent years pervades media reports, and some of the literature [11,64–66]. Whether or not this is the case is not easy to ascertain, given that these parameters and associated trends are much more difficult to determine, compared with area burned.”

    ”Indeed, there is increasing evidence, suggesting that there is, overall, less fire in the landscape today, than there has been centuries ago…”

    Doerr, Stefan H., and Cristina Santín 2016. “Global trends in wildfire and its impacts: perceptions versus realities in a changing world.” Phil. Trans. R. Soc. B

  • VooDude

    “Although an increasing frequency of forest fires has been suggested as a consequence of global warming, there are no empirical data that have shown a climatically driven change in fire frequency since the warming that has followed the end of the ‘Little Ice Age’. We present here evidence from fire and tree-ring chronologies that the post-‘Little Ice Age’ climate change has profoundly decreased the frequency of fires in the northwestern Québec boreal forest. A 300-year fire history (AD 1688-1988) from the Lake Duparquet area (48°28′ N, 79°17′ W) shows an important decrease, starting 100 years ago, in the number and the extent of fires. … The contradictory results between predicted and observed effects of warming on fire frequency call into question our present capability to generalize the effect of increasing CO2 levels on fire frequency.”

    Bergeron, Yves, and Sylvain Archambault 1993. “Decreasing frequency of forest fires in the southern boreal zone of Quebec and its relation to global warming since the end of the’Little Ice Age’.” The Holocene

  • VooDude

    “It’s an example of how climate change affects the way wildfires burn.”
    Nope.

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