America's intensifying drought

Intensifying Drought Shifts Toward Central U.S.

Robertscribbler,

12 March, 2018

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.