Fear of Rains: "The Mountains Are Loaded"
County Office of Emergency Management officials have rolled out a sweeping change in protocol for evacuations, saying it would better protect all communities below burn areas in future storms.
Twenty-four hours before the arrival of any storm that is forecast to bring half an inch of rain or more per hour to those areas, Sheriff Bill Brown said last week, he will issue a mandatory evacuation order blanketing all of Montecito and parts of the Carpinteria Valley.
Evacuations on this scale for mountainside communities next to the ocean are unprecedented but necessary, officials said.
“Nobody’s done this before,” said Rob Lewin, county emergency manager. “This is what they do in hurricanes. Let us not be fooled that the mountains have flushed the debris from the Jan. 9 storm. The mountains are loaded.”
What happened last time. On Jan. 7, when the county first issued mandatory and voluntary evacuation orders for Montecito, the National Weather Service was forecasting up to one-and-a-half inches of rain per hour from the approaching storm, the first of the winter.
The rain that came was much more extreme, however. Beginning at 3:34 a.m. on Jan. 9, the mountainside that had burned in the Thomas Fire above Montecito was hit with four bursts of intense rain; one of them dumped half an inch in five minutes.
The odds of that occurring were once in 200 years.
By 4 a.m., a massive torrent of mud and boulders was surging through the sleeping community below, overwhelming everything in its path. Twenty-one people died, and two are still missing.
“We knew we were going to have a bad storm,” Brown told a standing-room-only crowd at the Montecito Union School last week. “What we prepared for is not what we received.”
Science of weather. The protocol includes a pre-evacuation advisory 72 hours before a storm and a recommended evacuation warning 48 hours before.
In addition to communities below the Thomas Fire, the protocol applies to less populated areas on the Gaviota Coast, below the Whittier and Sherpa fire burn areas, and in the Santa Maria Valley below the Alamo Fire.
Half an inch of rain per hour is dangerous in the burn areas because it can trigger landslides and debris flows from loose boulders and soil no longer held in place by dense chaparral, scientists said. And now that some – but by no means, all – of the debris has been flushed out of the canyons, they say, water may be able to move faster through them.
“It will now take less rainfall to move debris than it did on Jan. 9,” Brown said.
Also problematic, scientists say, is a mountainside microclimate that has the potential to ratchet up rainfall amounts and intensities in the burn areas.
It happens like this: As storms approach the coast from the north, rotating counter-clockwise, they can generate strong winds from the south. These winds drive moisture-laden air off the ocean straight into the steep east-west trending slopes of the South Coast. The moist air cools rapidly as it is lifted upwards, and then packs a punch as it drops a load of rain high on the mountainside.
“Because of the extreme topography, the prediction for half an inch of rain per hour can easily result in something twice as much on those slopes above Montecito,” said Kevin Cooper, a biologist with the Los Padres National Forest who served on the federal Burned Area Emergency Response team for the Thomas Fire.
“It’s always worrisome in these situations. We could have an equally bad event as on January 9th; it just depends on how hard it rains,” he added.
That’s why the trigger for evacuations is a storm forecast and not the actual amount of rain that comes, Cooper said.
“You can’t wait for something to appear, because it’s like a snow avalanche,” he said. “It looks okay until it’s on top of you.”
“Live your lives.” County records show that rainfall intensities of half an inch per hour occur at least once on the South Coast almost every year. The risk of debris flows is greatest in the first year after a fire, but the evacuation protocol will be in place until the vegetation in the burn areas grows back, Lewin told the anxious crowd at Montecito Union.
“We want you to live your lives and have hope,” he said. “But you have to be prepared to have a bit of a transient life. Make sure you always have a suitcase ready and your gas tank full.”
The audience wanted to know how long it would take for the vegetation to grow back in the burn area. The unsatisfying answer was: one to five years, depending on the rain.
“Unfortunately, it’s not a simple thing,” Lewin said.
The status of green. In an interview, Cooper said he saw very few shoots of vegetation sprouting in the Thomas Fire burn area on a recent visit there. All of the trees are gone, he said, and there’s quite a bit of debris still piled up at the bottom of the creek canyons.
Artificial seeding of burned chaparral slopes has not been effective in the past, Cooper said. It can promote weeds, and if it is done too early, the seeds can be washed away in the rain. The native vegetation comes back just as fast as the seeds, anyway, Cooper said.
“There’s a great seed source still up there, and it’s growing,” he said of the slopes above Montecito. “It’s ready to recover. If we get light rains, it might be hard to walk through these burned areas next spring.”
Story and lead photograph by Melinda Burns, a veteran environmental and investigative journalist based in Santa Barbara.
Images: Federal scientists check status of Thomas Fire burn area; Chart by SB County and National Wether Service; Sheriff Bill Brown briefing after deadly mudslide in early January (SB Independent)'; Destroyed home in Montecito (Mike Eliason)