The eastern and western ends of the country have offered a stark study in weather contrasts in recent days.

On the West Coast, a heat wave has once again settled in, helping to fuel wildfires, one of which has destroyed dozens of homes, while on the East Coast, a string of thunderstorms wrung out massive rains over West Virginia and caused deadly flash flooding.

While it would take dedicated studies to estimate any potential influence from global warming on the odds of both events, both large wildfires and heavy downpours have been on the rise in the U.S. in recent decades. Both trends are expected to continue into the future if heat-trapping greenhouse gases aren’t curbed.

Hot, Tinder-Dry West

Wildfires are a familiar summer danger across the West because that is the region’s dry season, but heat waves can exacerbate the risk by drying out vegetation.

The scorching heat wave that sent temperatures in the Southwest to record-breaking levels last week, combined with dry, windy conditions, helped do just that, meaning there has been ample fuel for any sparks from human activity or lightning to grow into full-fledged conflagrations.

Now, another heat wave is settling in. While it’s less intense than last week’s, it is covering a larger area.

Several fires already broke out last week. The biggest one is the Erskine Fire, which is burning about 45 miles northeast of Bakersfield in central California. The fire has scorched more than 45,000 acres since it started on June 23 and subsequently exploded on the following day. The fire has reportedly killed at least 2 people and destroyed 250 structures, including homes.

While more favorable weather over the weekend helped the thousands of firefighters battling the blaze to get it 45 percent contained as of Tuesday, the shift to hotter conditions again could cause further problems as well as fuel other wildfires.

Erskine Fire

The Erskine Fire in California as seen by NASA's Aqua satellite.

Credit:

“Now that we're seeing a second wave, fire risk is even higher than it was earlier as fuels have already been primed to burn more intensely,” said Daniel Swain, an atmospheric science Ph.D. student at Stanford University. “Hopefully we don't see any major wind or dry lightning events in the near future.”

The additive effects of the heat are also a concern for public health, especially in urban areas that suffer from the heat island effect.

“Successive days and weeks of well above average temperatures — especially at night — can cause progressively greater stress upon the human body,” Swain said,  “especially in individuals who are more susceptible for one reason or another,” such as the very young and old and those with particular medical conditions.

Teasing out any potential influence from climate change in fueling this and other fires is tricky because of the large number of factors that contribute to them. However, recent Climate Central research has found the average annual number of wildfires in the West that burn more than 1,000 acres has tripled since 1970. Such wildfires burn on average six times as much area today and the fire season is 105 days longer.

The wildfire concerns this summer won’t go away anytime soon as seasonal forecasts from the National Oceanic and Atmospheric Administration suggest above-average temperatures are likely to continue for the remainder of the season.

Deluge in the East

The situation was the polar opposite on the other side of the country: On Friday, a frontal system collided with an area of extremely moist air over West Virginia and  “it just absolutely blew up,” sending torrents of rain down on the state, said Andrew Beavers, a meteorologist with the National Weather Service office in Charleston.

West Virginia flooding

Emergency crews take out boats on a flooded I-79 at the Clendenin Exit in West Virginia on June 24, 2016.

The impact of the rains was compounded by two other factors, he said. One was that the storms “went over the same sites over and over and over again,” a situation called “training.”

The other was that the steep slopes and narrow valleys of the local terrain meant those valleys saw significant runoff and therefore flooding. “There’s nowhere for all that rain to go” except down, Beavers said.

One of the worst hit areas was around White Sulphur Springs, which recorded a stunning 9.17 inches of rain in 48 hours — the bulk of it, more than 8 inches, fell in less than 24 hours. Several other areas saw more than 5 inches in 24 hours.

The massive floods that rapidly inundated towns displaced thousands and damaged or destroyed thousands of homes and other structures. At least 23 people were killed, according to news reports.

 

 

The meteorological setup that led to the heavy rains and floods is fairly rare for the region, Beavers said. The Charleston NWS office said that it was a 1-in-1,000-year event for them, or one that has only a fraction of a percent chance of happening in any given year.

While such heavy downpours have been on the rise nationally and are expected to become more common and more intense as temperatures rise, saying something about the potential role of warming in this particular event is difficult.

That is because the storms were localized and driven by convection, and climate models have a difficult time accurately capturing such features, said Friederike Otto, of Oxford University's Environmental Change Institute, who works on such attribution analyses with the Climate Central World Weather Attribution program.

More widespread extreme rainfall, like that which recently deluged parts of France, are easier to analyze and therefore to tease out the influence of warming, she said.