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Rain and fire is a 'double jeopardy' situation, scientists say

A largely forgettable rainfall provoked a growth in vegetation that, followed by a hot, near-record dry period, simply resulted in more fuel for potential wildfires.

May 14, 2013|By Hector Becerra, Los Angeles Times
  • Crews from Manhattan Beach work on a hillside behind homes threatened by a major brush fire in Newbury Park in early May. Recent rains awakened dormant vegetation, which became a source of more fuel for potential fires.
Crews from Manhattan Beach work on a hillside behind homes threatened by… (Brian van der Brug, Los Angeles…)

When it comes to Southern California's increasingly perilous fire season, you can blame both the lack of rain and the little rain we did have.

Scientists at NASA's Jet Propulsion Laboratory and at Chapman University said satellite data show the effects of a steady and largely forgettable rainfall during a roughly four-day period at the end of January.

JPL scientist Son Nghiem said the rain came just as much of the vegetation throughout the region was awakening from a dormant stage.

The rain provoked a growth in vegetation that, followed by a hot, near-record dry period, simply resulted in more fuel for potential wildfires. The situation was a true "double jeopardy" one, Nghiem said Monday.

"This timing enhanced vegetation growth early this year, particularly in Ventura County, supplying significant new fire fuel despite one of the driest overall rainfall seasons on record," he said. "Had the rains fallen earlier, when the vegetation was in a dormant state, the effects would have been minimal."

Scientists said the satellite data could be used to give fire agencies a broad picture of where the greatest danger lies. The Indian satellite tracked soil moisture levels. The NASA satellite tracked the moisture level of vegetation.

Nghiem said scientists were already working to help fire agencies assess fire danger conditions by using satellite data, and that "tremendous progress" has been made. He said the latest data reinforce the potential of the technology, which can gather information from places that might be inaccessible either because of the terrain or a lack of resources.

"If we can show that the satellite data is useful to help fire agencies make assessments of wildfire danger," there's a potential to create something that can warn officials "in near real time," Nghiem said.

"Within minutes, the data can be turned into a kind of work product that can be directly used by fire agencies," he said.

Southern California's wildfire season got off to an ominously early start because of dry conditions even during the region's nominally wettest months: January, February and March. On top of that, strong Santa Ana winds buffeted the region during a time of year they normally don't.

Earlier in the month, the Springs fire in Ventura County grew into a monster of more than 28,000 acres that was fanned by winds that blew over desiccated scrublands.

On Monday, fires along the Grapevine and near Lytle Creek kept crews busy during a heat wave. No structures were damaged, but the blazes forced the temporary closure of lanes along both the 5 and 15 freeways.

Rich Thompson, a meteorologist for the National Weather Service in Oxnard, said Monday brought blistering temperatures in the high 90s and low 100s in the San Fernando Valley and elsewhere.

Beginning Tuesday, temperatures should steadily decline, and they could plunge all the way to the 70s by Wednesday. But, he said, they're expected to head back up by Sunday and Monday.

"You've got to love the spring in Southern California," Thompson cracked.

Southern California got most of its moisture of the rain year — measured from last July to June 30 of this year — from fall through December. But then, as if a spigot got turned, it all but stopped.

Just over an inch of rain fell in January, but most of it came during a few days late in the month, and especially Jan. 24 and 25, said Bill Patzert, a climatologist at JPL.

"That was our last gasp of rain" for several months, he said. "After that, rain was ephemeral to whimsy."

Nghiem said the rain at the end of January spurred vegetation growth.

"That put water into the soil at a time when the vegetation was waking up from the dormant state," Nghiem said. "It provided water at the right time for the vegetation to grow very fast."

That wouldn't have been a problem had it kept raining, as it can during the winter months. But instead it just got dry and windy, he said.

Nghiem said satellite data showed just how quickly the situation turned after the late January rainfall. A Feb. 25 image of Riverside County — which recently had a large wildfire — shows a landscape color-coded in green to indicate the elevated moisture levels of the vegetation. An image from May 1 shows a different situation.

"In February, you see a lot of green," Nghiem said. "Then on the first of May, all the green is gone. That's exactly where it burned."


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