Did the recent rain reduce wildfire risk in the SF Bay Area?


Northern California obtained a soaking of rain that is thought-about spectacular for mid-September. Summer time is not even over, and plenty of areas across the San Francisco Bay Space recorded 0.5 to 2 inches of rain Saturday via Monday.

What does this imply for wildfire season within the Bay Space, which normally sees its most harmful fires in September and October when desiccating offshore winds choose up after vegetation on the bottom has dried out all summer time lengthy?

The quick reply, in line with the consultants SFGATE contacted, is that the rain will certainly stall the beginning of peak wildfire season — and the way lengthy that delay lasts depends on what occurs subsequent. 

“It’s positively going to scale back fireplace threat via fall,” mentioned Craig Clements, director of San Jose State College’s Hearth Climate Analysis Laboratory and a professor on the college. “It could be nice if we had one other storm. Then we might be in even higher form. If we get a warmth occasion, after which get a wind occasion, and don’t get any extra rain, we may very well be in hassle once more.”

The rains dampened the area, and that may typically decrease the fireplace threat, however there are nuances in how the moisture impacts totally different components of the panorama. The bushes and enormous shrubs will see little influence from the rain as they’re severely drought-stricken from years of below-normal rain and so they want a number of storms and extra time to get well, however the soil itself will suck up the moisture and make it harder for fires to start out and burn. 

“When you have sizzling, dry soil, it burns in a different way from moist soil that is cooler and places out humidity,” defined Jonathan Cox, deputy chief of Cal Hearth’s San Mateo County division

Most wildfires within the Bay Space begin in grasses, and the rain will assist make the grass-covered hills much less flammable within the short-term.

“We might see a grass crop pop up, and if we get a grass crop, that’s not essentially unhealthy as a result of it might be inexperienced,” defined Clements, director of San Jose State College’s Hearth Climate Analysis Laboratory and a professor on the college. “That will take some vitality out of the fireplace if there have been an ignition.”

However whereas the contemporary inexperienced grass may very well be helpful within the coming weeks, the pre-existing lifeless grass will get little profit from the rain. “That stuff is lifeless; it’s not sucking up rather a lot soil moisture,” Clements mentioned. “The issue is that grass is able to burn once more after we get some wind and sizzling climate.”

The Bay Space’s most devastating fires, such because the 2019 firestorm within the Wine Nation, have occurred when offshore winds blow sizzling air from inland areas towards the coast. As of Tuesday, there are not any offshore winds within the rapid forecast, however fall is the season for them, and there is nonetheless time for the blustery situations to develop.

“I feel one of the best ways to place it’s we have now a historical past of offshore wind occasions in Northern California,” mentioned Cox. “It might not occur this yr or we could get a number of in a row. Till we get a number of measurable rain occasions that actually transfer the needle on the drought, we have now concern that the panorama might be inclined to fireplace.”

Backside line: “The rain helped, however we’re not out of the woods but,” Clements added.

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