Fires in California

Fires in the USA

7 November 2007

Burn Scars Across Southern California

The explosive wildfires of October 2007 in Southern California killed severalpeople, scorched hundreds of thousands of acres, and destroyed more than twothousand homes. Based on acres burned, two of the fires, the Witch and HarrisFires, climbed into the record books of the state’ 20 largest wildfires (basedon statistics kept since the early 1930s.) In terms of structures burned, fourof the October fires made the list of the top 20 largest fires: the Witch,Harris, Slide, and Rice Fires. As of 5 November 2007, nearly 1.3 million acreshad burned in wildfires in Southern California. That total included the240,000-acre Zaca Fire, which burned during July and August.

31 October 2007

This image of Southern California, centered on Los Angeles, shows how widespreadand large the October 2007 fires were. Captured by the Moderate ResolutionImaging Spectroradiometer (MODIS) onNASA’s Terra satellite on 31 October, theimage is made from a combination of visible and infrared light to make burnedareas (brick red) stand out from unburned vegetation (bright green). Desert orsemi-arid landscapes are beige, dense urban areas are gray, and water is darkblue. Burn scars from previous seasons, such as the 2006 SawtoothComplex Fire and the 2003 SimiIncident Fire have faded to light pink.

The large image provided above have a spatial resolution (level of detail) of250 meters per pixel.

Winds Blow Smoke in California

In addition to the dangers that a wildfire’s flames pose topeople, wildlife, and property, the smoke that they billow out poses a healthhazard over an even larger area. Smoke not only contains carbon monoxide, whichis poisonous, it also contains tiny soot particles that can work their way deepinto people’s (and other animals’) lungs, causing respiratory irritation anddistress. During the firesin Southern California during the fourth week of October, the air quality inmany areas deteriorated to levels that the Environmental Protection Agencycategorizes as “unhealthy.”

This pair of images shows the location and thickness of smoke on October 24and 26 combined with arrows showing wind speed and direction. The smoke wasobserved by the Ozone Monitoring Instrument on NASA’s Aura satellite. OMI measures how much the smoke particles (aerosols) reduce theintensity of sunlight reaching the Earth’s surface. Places where aerosols werethickest are colored pink, clear air is transparent, and clouds are white. Whitearrows show wind patterns at about 3 kilometers altitude (data is from theNational Weather Service’s National Centers for Environmental Prediction). Thelonger the line, the stronger the wind.

24 and 26 October 2007

During the first days of the fires, strong Santa Ana winds blew steadilyoffshore from the high-altitude deserts of the Great Basin; smoke spread far outover the Pacific. On October 24 (top), the Santa Ana winds began to weaken (windarrows are much shorter). The winds continued to make a large, clockwise spiralaround an area of high air pressure over the Four Corners area of the Southwest,and smoke was pushed north as well as west. By October 26 (bottom), winds overCalifornia were onshore, and the smoke from the still-smoldering fires spreadnortheastward into Nevada, Arizona, and Utah. By October 27 (last frame ofanimation), smoke had reached Colorado.

Santa Ana winds are a common occurrence in Southern California in the fall.Cold air often sinks into the Great Basin deserts to the east of California. Asthe air piles up at the surface, high pressure builds, and the air begins toflow downslope toward the coast. When winds blow downslope, the air getscompressed, which causes it to warm and dry out. In fact, the air can warm at arate of 10 degrees Celsius per kilometer of descent (29 degrees Fahrenheit permile). Canyons and passes funnel the winds, which increases their speed. Suchwinds spread fire and smoke, and they also dry out vegetation, making it evenmore flammable.

(source: EarthObservatory)

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