three months after Harvey’s record rains, Southeast Texas is
experiencing drought. No, this is not quite normal despite a mild La
Nina exerting a drying influence. Image source:U.S.
Drought Monitor. Hat
tip to Eric Holthaus.)
did this happen? How did so much water disappear so soon? How could
an instance of one of the most severe floods due to rainfall the U.S.
has ever experienced turn so hard back to drought in so short a time?
a sentence — climate change appears to be amplifying a natural
switch to warmer, drier weather conditions associated with La Nina.
course, climate change does not exist in a vacuum. Base weather and
climate conditions influence climate change’s impact. At present,
with La Nina emerging in the Pacific, the tendency for the southern
U.S. would be to experience warmer and drier conditions. But in a
normal climate, these conditions would tend to be milder. In the
present climate — warmed up by fossil fuel burning — the tendency
is, moreso, to turn toward an extreme. In this case, an extreme on
the hot and dry end of the climate spectrum.
the region of Southeast Texas flooded so recently by Harvey’s
record rains, it means that a turn from far too wet to rather too dry
took just a little more than 3 months.
Texas, however, is just one pin in the map of a larger trend toward
drought that is now blanketing the South. Over the past month,
precipitation levels were less than 50 percent of normal amounts in
most locations with a broad region over the south and west
experiencing less than 10 percent of the normal allotment of
moisture. Meanwhile, 90-day
precipitation averages are also much lower than normal across the
drought conditions are widespread as severe to extreme drought is
starting to crop up in the South-Central U.S. With La Nina likely to
continue through winter and with global temperatures in the range of
1.1 to 1.2 C above pre-industrial averages, there is risk that
conditions will intensify. Image source: U.S.
upshot is that moderate drought is taking hold, not just in southeast
Texas, but across the southwest, the southeast, and south-central
U.S. Severe to extreme drought has also already blossomed from
northern Texas and Louisiana through Oklahoma, Arkansas and Missouri.
This is relatively early to see such a sharp turn, especially
considering the fact that La Nina conditions have only lasted for a
short while and have, so far, been
rather mild on the scale of that particular climate event.
like Texas, many of these drying regions experienced extreme rainfall
events during spring and summer. Such events, however, were not
enough to stave off a hard shift to drought in a world in which
human-caused climate change is now driving both droughts and more
extreme rainfall events to rising intensity.
temperature and precipitation variance from normal over next three
months. Climate change is likely to enhance this variability related
feature. Image source: NOAA.)
other words, there is not insignificant risk that the hard turn away
from record wet conditions in the South will continue and that severe
to very severe drought conditions will tend to spring up and expand.
La Niña means drought is now expanding in Texas, even though we're just three months after Hurricane Harvey's record-setting rainfall. Yes, this will be Houston's rainiest year in history. Yes, they'll probably end the year in a drought.