A plane monitoring the so-called Rough Fire in the Sierra National Forest last month in California. Credit Max Whittaker/Reuters

FRESNO, Calif. — The air in the San Joaquin Valley hangs thick with gray-brown dust, a result of the state’s largest fire, which has burned through more than 160 square miles in the nearby hills.

The fire has so far spared lives and homes. But it has exposed one of the obscured effects that four years of record drought has unleashed here: dangerous drops in air quality that exacerbate public health problems in this region and threaten to choke the quality of life.

“With the fire, even with my inhaler, I’m still wheezing,” Antoinette Wyer, 48, an asthmatic who has lived her whole life here, said at a health clinic on Wednesday. She has kept her 3-year-old grandson inside this week, while a 4-year-old grandson has stayed home from school.

The dreadful conditions here — with temperatures soaring over 100 degrees, dry brush everywhere and a miasma of bad air — seem likely to become more common throughout the Western States, where the fire season is shaping up as a record one. This summer, residents of Denver grappled with air pollution that had wafted down from wildfires in Canada; throughout the West, a big blaze in one place can be felt many miles away.

The Stanislaus Hotshots hiking on a fire line in the Sequoia National Forest. The so-called Rough Fire has burned through more than 160 square miles. Credit Max Whittaker/Reuters

In Fresno County, elementary schoolchildren have been kept inside during recess this week because of the soot in the air that blots out the sun, and the Clovis school district may cancel a football tournament this Saturday for the same reason. Public health officials are warning people with heart and lung problems to stay inside. And asthma clinics around Fresno are overflowing with new patients. Normally, particulate matter levels in the air spike in the winter but drop during the summer, said Seyed Sadredin, the executive director of the San Joaquin Valley Air Pollution Control District.

But since the drought began, the volume of particles in the air has been spiking year-round, for a variety of reasons: Rain does not clear the air; dust from dry, fallow fields and from farmers digging wells kicks up more easily; and the longer wildfire season means more smoke in the air more often.

The San Joaquin Valley lies at the center of the state, surrounded by mountain ranges on the east and the west, receiving little coastal air. The air and soot are effectively trapped in a geographic bowl for much of the summer, and the lack of wind and rain has made it impossible for things to clear out.

Mr. Sadredin said that if the drought continued much longer, it would threaten much of the progress the region has made to lower air pollution levels.

“We have the toughest air regulations in the nation, but we have no control over the geography and the climate,” he said. “The Valley is basically a bowl with a lid on top for most of the year.”

Dr. Vipul Jain, a pulmonologist who runs a chronic lung disease program in Fresno, said the effect of the drought and fires was likely to get worse this week, with temperatures expected to soar to 106 degrees. He said that hospitals could have as many as double the number of patients for acute lung problems in the coming days and weeks.

“It’s kind of a worst-nightmare situation,” said Dr. Jain, an associate professor at the University of California, San Francisco. “And the worst is still yet to come. We can see it, but anyone with a lung problem, they feel it, and there is no way to prevent an exacerbation of their problems. People have to go outside and work, and they will suffer.”

For years, California has had the most polluted air in the country, with cities here dominating national lists of the dirtiest urban areas. And the Central Valley has had the worst air in the state for decades: More than 20 percent of all children in the Central Valley have asthma, according to the American Lung Association.

Many counties throughout the state and the San Joaquin Valley have successfully reduced the amount of ozone in the air. But levels of soot, or particle pollution known as PM-2.5, have started to increase after years of decline, according to state figures. Officials are blaming the drought.

At local asthma clinics, doctors have had an explosion in business since the drought began. Dr. Malik N. Baz said his asthma and allergy practice had grown at least 20 percent each of the past three years, and he has opened five new clinics around the Valley in the past two years — all of them overflowing with patients.

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After Years of Drought, Wildfires Rage in California

“Our only limitation right now is that there aren’t enough parking spots because there are so many people coming in,” Dr. Baz said, adding that he could open more clinics if he could find more doctors willing to move here. “Right now, pollution is so high, I even started coughing when I went to Starbucks to get coffee — and I don’t have asthma.”

As the drought has dragged on, the soot has left the Sierra Nevada covered for weeks at a time. Dust clouds dot the rural roads here, and there is often a stripe of gray haze at sunset. Residents routinely avoid the outdoors in the summer or when they see (or, worse, feel) the film in the air. Sometimes, the air has been so thickly clouded with pollution that it is difficult to see across the California State University football stadium here.

Increasingly this summer, even healthy adults have grown wary of spending time outside. On Wednesday, with soot from what has been called the Rough Fire still blowing into town, some traded morbid jokes, comparing living here to smoking and wondering how many years they were taking off their lives.

“It started last week, with eyes burning, congestion, can’t sleep at night,” said Randall Cooper, 62, a retiree who moved here from the Bay Area 10 years ago. Those who could have tried to flee, often to the coast for the weekend. But this remains one of the few affordable places to live in California, which keeps many people here, even as the local economy continues to suffer under the drought’s weight.

Mr. Cooper said his nose had cleared up when he went to the Bay Area for his son’s wedding, but grew clogged again as soon as he came back.

“I think about leaving, but from here to the Bay Area, every mile is $1,000 more in housing,” he said. “I wasn’t raised here. There are a lot of people who have had to deal with this their whole lives.”

Air and health officials have traded red-coded warnings that indicate “unhealthful” air for purple, calling them “very unhealthful.” But everyone has to go outside sometimes.

Juliet Johnson, 52, has lived in the San Joaquin Valley for nearly four decades and has severe allergies and asthma. She went for a walk with her dog on Monday, despite the “campfire smell” in the air, and woke up Tuesday with no voice.

“It was so nice out, so I opened up all the windows in my house over the weekend,” she said.

Dr. Jain warned the situation was likely to grow worse. Medical studies have shown that asthma hospitalizations reach their peak in September, and the fire season will not be over by then.

“What we have now makes the good-air days bad and bad-air days worse,” he said. “It jacks up the air to a whole ’nother level. What the fire and particles do is like sunburn in their lungs, putting the smoke right down in their lungs. We see a whole bunch of people get exacerbated and getting hospitalized, no matter what we do.”