California Wildfires: A closer look

California's future climate favorable for wildfires: experts

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Dr. Mario Picazo

Meteorologist, PhD

Wednesday, December 20, 2017, 13:22 - This month, scientists are pointing at climate change to explain why California wildfires have become so devastating in recent years. Not only are these mega wildfires becoming more frequent, they are also more widespread and intense.

Professor Alex Hall, a climate change expert at UCLA's Department of Atmospheric and Oceanic Sciences and member of the panel of climate scientists that asses the IPCC report, confirms that the sequence of climate events lived in the state over the past few years is what we should expect to see as part of California's future climate scenario.

Fall is the time of the year when wildfires are more common in California. Strong winds produced by a high pressure center with a steep pressure gradient normally positioned over desert areas of Nevada and Utah, help trigger, propagate and intensify the fires.

As the air pushed by these desert winds moves towards the coast, it sneaks through canyons and passes where it can further speed-up. Known as Diablo Winds in northern California and Santa Winds in the south, they are also characterized by becoming warm and dry as they compress and heat due to the elevation difference between plateau (origin) and coast (final destination).

Postdoctoral scholar Daniel Swain from the UCLA Institute of the Environment and Sustainability confirms that Santa Ana winds have been driving the current Southern California fires, but adds that the recent climate scenario in Southern California has a lot to say as well. The period between October and November 2017 was the warmest and second driest on record in coastal Southern California including Los Angeles.

This year the ingredients where all there in the right place and at the right time for a very active Fall fire period to occur. After years of intense drought, this past winter was exceptionally wet, and the then came a scorching summer and a very dry and mild Fall. All the very abundant vegetation from the winter rains turn into fire fuel, and with the first spark came the Santa Rosa fires in the north, and now the greater Los Angeles fires in the south.

October normally marks the end of the active fire season, but this year has extended in full force all the way through December.

According to Glen MacDonald, a professor in the UCLA Geography Department and in the Institute of the Environment, "the American Southwest is experiencing an unprecedented climate state in which variations in temperature and climate have been magnified".

A home's remains are seen, next to a burnt out truck, after they were destroyed, during a wind-driven wildfire in Ventura. REUTERS/Mike Blake

MacDonald has it clear, "we will have a wet year when the fine fuels will grow and accumulate, and then we will be hit by very dry conditions, which will dry out soil surfaces and vegetation, then the fuel from the wet year is going to cause fires during dry periods. That is the worst of all possible worlds, and that is what keeps me awake at night."

When it comes to the relation between California wildfires and climate change, professor Alex Hall stresses that "Southern California fires are very, very weather driven". He says, "If you change the weather, you would imagine that fires might change too, and that's exactly what we have found in recent research."

One of the methodologies used to study past fire activity in California and other areas of the southwest is tree ring analysis. Trees are sensitive to soil water and moisture availability, so the rings give scientists visual information about precipitation, evaporation and other temperature patterns. During dry years, trees grow less and rings are closer. In wet years the pattern is opposite and rings are further apart.

For MacDonald "they are a wonderful archive of climate history, but with climate change turning up the heat these days, fundamental variables like ocean temperatures, evaporation or snowmelt are changing, and that means we are headed into uncharted territory."

As yearly temperature and precipitation variability increases due to climate change, there is a greater contrast between drought and wet years, and that can mean a considerable increase in fire risk across many areas including California.

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Thumbnail image courtesy: Reuters