A recent survey of the Sierra conducted by the U.S. Forest Service paints a disturbing picture of the fuel conditions across Central and Southern California.
Continuous drought the past five years has weakened trees, allowing them to be susceptible to the bark beetle. The recent number of dead trees in the Central Sierra is 66 million, providing a heavy concentration of dead and highly combustible fire material, especially in the Sierra and Sequoia National Forests.
Tree mortality is nearly uniform in these areas, with broad expanses of dead trees as opposed to the patchwork of dead trees from a year or two ago.
According to the Southern California Geographic Coordination Center (SCGCC), relatively pleasant temperatures of May and early June were replaced by well-above normal temperatures over central and southern California during the last two weeks of June.
While the heatwave didn’t last long, it was intense enough to cause rapid curing of all fuel types across the entire region, and several large fires quickly developed during the peak of the heatwave. Two large fires in the Angeles National Forest exhibited rapid rates of spread, even during the absence of wind.
Once winds kicked up a few days later, the Erskine Fire in Kern County June 23 exploded to more than 48,000 acres, destroying 285 homes.
The SCGCC feels that this year’s summer weather pattern will likely be different than the pattern last summer, in which broad areas across the Pacific had well-above normal sea surface temperatures (SST).
The above normal SSTs included an area off the coast of Baja which is often the spawning ground for tropical systems. A few remnants of these storms brought thunderstorms with heavy rainfall quite frequently last year.
This year, SSTs are much lower - in fact, much of the Pacific now has below normal SSTs. This temperature profile will be much less conducive for thunderstorm activity, however,
while there will likely be fewer thunderstorm days this year, there may be a higher risk of ‘dry’ thunderstorms with lightning. Last year, nearly every storm that formed was wet, as a saturated airmass allowed heavy rain to fall from most of the storms.
Therefore, despite the high amount of lightning, the number of new fire starts from thunderstorms was low last summer. This year, a much higher proportion of the storms may be dry compared to past few years.
Given the extremely dry fuel status across the entire area, it would only take one sizable outbreak of dry lightning to generate a heavy amount of fire starts. Due to the possibility of dry lightning and the dry fuels, a higher than normal threat of large fires could take place through summer and early fall.
Any lightning outbreak in these areas could easily spark vegetation fires. Large fires will continue to be highly resistant to control efforts during hot and windy periods, and large fire potential may not fall to near normal levels before November or December.
The combination of extremely dry fuels, along with the potential for dry lightning this summer, may result in the busiest and most dangerous fire season in years, the report concluded.