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Worsening Prairie Fires: Exceptional Central Heat and Drought Spurs More Oklahoma Blazes

Today, as with many recent days, Oklahoma is experiencing hot, dry, critical fire hazard conditions. And over the past month, historically exceptional drought and hotter than normal weather have spurred a spate of very severe and seemingly unrelenting wildfires across the state.

(The Rhea Fire burned nearly 300,000 acres in Oklahoma during mid-April. This large fire is now 100 percent contained. But blazes continue to break out. Image source: Climate.gov.)

During mid-to-late April, the Rhea Fire scorched 286,000 acres destroying more than 50 homes and killing hundreds of cattle. At about the same time, the 34 Complex fire burned through 62,000 acres and forced many Oklahoma residents to evacuate. For reference, the massive Thomas Fire which burned hundreds of structures in California this past December was 240,000 acres in size.

Unfortunately, severe fire conditions continued through today with 500 acres going up in flames near Pawnee Oklahoma in just the past 24 hours. In total, about 350,000 acres have burned so far this year (an area half the size of Rhode Island), numerous structures have been destroyed and an estimated 2,000 cattle have likely been killed. With severe drought, heat, and extreme fire conditions expected to continue throughout at least the next month, there is little relief in sight.

 

(The U.S. Drought Monitor shows severe dry conditions expanding across the Central U.S. during early 2018. Long range forecasts show drought continuing or worsening over Central and Southwestern States over the coming months. Image source: Drought Monitor and NOAA.)

The causes of the present fire hazard are quite clear. Throughout fall, winter, and spring, the Central U.S. has experienced both hotter and drier than normal conditions. During recent weeks, drought in this region has become exceptional — the highest drought category provided by the National Drought Monitor. In addition, strong, warm south-to-north winds have tended to prevail over the region. These winds have rapidly fanned many recent Oklahoma fires to massive size.

Over the coming month, this drought is expected to dig in as temperatures warm. And, as a result, fire danger is expected to be quite high for a broad region of the U.S. South stretching from just west of the Mississippi all the way to California.

(Above normal wildfire potential is expected to remain in place for Oklahoma even as risks rise for neighboring states. Image source: NOAA.)

Though spring wildfires do occur across Oklahoma and parts of the plains states, the trend has been for an increasing large fire incidence. This trend, in turn, has been driven by human-caused climate change. For as the U.S. has warmed, the rate of evaporation from soils, vegetation and lakes has increased. This higher rate of moisture loss both intensifies drought and spikes fire risk.

Warming and worsening drought has been a particularly acute set of affairs for Central and Western states. The number of weeks when large fires are a risk has increased from 50 to 600 percent for most of these regions. In other words, if it seems like there are more large fires, it’s because there are. And what we see now are spring prairie fires that are far more intense than they were in the past.

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Intensifying Drought Shifts Toward Central U.S.

Last week saw a major increase in drought intensity in the Central U.S. as flash wildfires sparked across Oklahoma. Meanwhile, longer term drought trends remained strong even as the U.S. West Coast saw breaks in the dryness in the form of late winter precipitation.

(Drought expanded across the Central U.S. last week as precipitation deficits there increased. Image source: Drought Monitor.)

A return to severe to exceptional drought across the Western and Central U.S. was one of the hallmarks of the overall warm winter of 2017-2018. Historic drought, which had been suppressed by substantial rains during 2016-2017, appears to have returned — with threat of worsening conditions through spring, summer and fall.

In the Central U.S., the dry pattern reinforced this week which added to already serious conditions. During mid-week, Oklahoma saw the eruption of seven large brush fires as a result of both drought and strong winds sweeping across the plains states. Dry springs can result in fires for this region. However, the recent intensification of droughts brought on by human-caused climate change is spiking fire hazards from the Central U.S. through the West Coast and beyond.

(California snow pack totals remain well below average despite a recent increase in the number of storms affecting the state. Image source: CDEC.)

In California, snow packs are still running well below average, despite a recent wave of storms sweeping through the region. But it’s worth noting that though still much diminished from typical snow depth totals, the present range is now higher than the driest years — 2014-2015 and 1976-1977. So the situation isn’t looking quite so bad as it was a few weeks ago.

In addition, the blocking ridge that had dominated the West for much of the winter has mostly collapsed — allowing more rain and snow-bearing storms to cycle through. Some relatively intense precipitation is expected to fall over central and northern parts of the state later this this week. However, with widespread drought reasserting and with warmer than normal temperatures likely this spring, the increasingly drought-prone state is far from out of the woods.

(Temperatures have tended to remain above average across most of the U.S. this winter even as abnormally dry conditions impacted the Southwest. Image source: NOAA.)

Under human-caused climate change increasingly warm temperatures result in higher rates of evaporation from lakes and soils. This increases drought intensity for many locations around the world. In keeping with this longer-term trend, the winter of 2018 can still be characterized as both warmer and drier than normal for most of the U.S. But the overall drought pattern has shifted more toward the Central U.S. and away from the West Coast with the approach of spring.

 

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