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Intensifying Drought Shifts Toward Central U.S.
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.
