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Exceptional Drought Blankets 58 Percent of California; Reservoirs Missing One Year’s Worth of Water
Robertscribbler,
31 July, 2014
For
California, the punishment just won’t stop.
Human
warming and a climate change induced blocking pattern have withered
California under record drought conditions for the better part of
three years now. A vicious trend that worsened again in recent days
with yet another jump in drought severity as exceptional drought
conditions surged to cover a majority of the state.
Previous
week’s values of 36 percent exceptional drought coverage rocketed
to 58 percent in just one week. Exceptional drought is the highest
drought category for the US Drought Monitor, representing the most
extreme conditions in the measure. So most of the state is now
sweltering under the nation’s worst drought category with the
remainder covered by extreme and severe drought:
(US
Drought Monitor map
of California showing 58 percent of the state covered in exceptional
drought [brick red], 23 percent covered in extreme drought [red], and
the rest covered in severe drought [orange]. California is now
entering its fourth month of 100% drought coverage after more than
three years of abnormally dry conditions.)
One
hundred percent drought coverage with worsening conditions has been
the prevailing pattern ever since May when drought first surged to
blanket the entire state. Since that time, conditions have been
steadily worsening with agricultural regions drying out, farmers,
communities and industries forced to further deplete limited ground
water supplies, and with reservoirs dropping despite best efforts by
federal and state officials to conserve.
As
a result, state supplies are being hammered. For, according to a
report released today by the National
Drought Mitigation Center,
the state is “short more than one year’s worth of reservoir
water, or 11.6 million acre-feet, for this time of year.” In other
words, if a year’s worth of rain fell over the state tomorrow, it
would barely be enough to bring reservoir levels back to normal.
So
far, drought effects have been mitigated, mostly through the
above-mentioned reliance on ground water supplies. But it remains
questionable how long such activities can continue. And despite even
these efforts thousands of agricultural workers have been laid off
amidst a 2 billion dollar loss for the state’s food industry.
As
ground water and reservoir levels continue to drop, officials have
grown more anxious to enforce conservation measures. To this point,
fines in excess of 500 dollars have been levied for residents hosing
sidewalks and driveways, for excessively watering their lawns, or for
other water intensive practices. To this end, many municipalities
have hired ‘water police’ to patrol neighborhoods and enforce
water conservation measures.
Climate
Change and A Mangled Jet Stream
Recent
scientific studies have made a strong link between the historic
California drought and ongoing changes to Earth’s climate resulting
from human greenhouse gas emissions.
Many of these changes involve heat-driven alterations to Earth’s
atmospheric circulation. For as the Earth warms, it does so unevenly.
In regions near the pole, and especially above 60 North, temperatures
have risen by, on average, about 0.5 degrees Celsius per decade since
the 1980s. This heating has pulled the Jet Stream along with
prevailing weather patterns northward.
(A Sierra Nevada mountain range featuring glaciers turned brown and sweltering under temperatures as high as 70 degrees on July 25, 2014. For 2013 to 2014, the Sierra Nevadas have been mostly devoid of the reservoir-restoring snows that California typically relies upon. Image source: LANCE-MODIS.)
This
more rapid heating of the far north has also resulted in a reduction
of the north-south temperature differential. In the past, a high
difference in temperature from north to south helped drive a
prevailing wind pattern called the Jet Stream which kept weather
systems moving across the Northern Hemisphere. But as the difference
between north and south temperatures dropped, weather systems tended
to stall. High amplitude waves tended to form in the Jet Stream and
blocking patterns tended to emerge more often.
For
California, the upshot has been the increasing prevalence of a ridge
and blocking high pressure system deflecting storms away from the
California coast. The pattern, which began to take hold three years
ago, has been an almost constant feature for the past 16 months. And
the result has been one of the worst droughts California has ever
seen.
In
May, a
new scientific study linked
the anomalous blocking pattern, the California Drought and human
caused climate change stating:
The
2013–2014 California drought was initiated by an anomalous
high-amplitude ridge system. The anomalous ridge was investigated
using reanalysis data and the Community Earth System Model (CESM). It
was found that the ridge emerged from continual sources of Rossby
wave energy in the western North Pacific starting in late summer and
subsequently intensified into winter. The ridge generated a surge of
wave energy downwind and deepened further the trough over the
northeast U.S., forming a dipole. The dipole and associated
circulation pattern is not linked directly with either El
Niño–Southern Oscillation (ENSO) or Pacific Decadal Oscillation;
instead, it is correlated with a type of ENSO precursor.The
connection between the dipole and ENSO precursor has become stronger
since the 1970s, and this is attributed to increased greenhouse gas
loading as
simulated by the CESM. (emphasis added)
This
climate change induced blocking pattern has also been associated with
numerous warm air invasions of the Northern Hemisphere polar
region, the
most recent of which occurred yesterday.
Models
Show Worsening Drought Conditions Under Human-Caused Climate Change
Unfortunately
for California, the US Southwest, and for a growing portion of the
country, the most recent drought may be just one in a string of many
increasingly worsening events to come. Climate models predict a
wholesale drying out of the US Southwest and Central US under an
intensifying regime that has already begun to take hold. By
mid-century conditions are expected to be quite extreme indeed:
(NCAR model study of global precipitation under moderate warming throughout the 21st Century. The scale is based on the Palmer Drought Severity index with values of -4 and lower at exceptional drought. Under this model run, most of the US is blanketed by exceptional drought conditions. Overall, drought is expected to originate in the south and central US and then expand north and eastward as human caused warming intensifies.)
For
Californians suffering under a three year long drought, such
long-range forecasts indicate that the worst may be yet to come. For
the short-to-middle-term, the west coast blocking pattern remains in
place and shows little sign of movement. For the long-term, unless
human greenhouse gas emissions are rapidly reduced, droughts of this
intensity grow more and more likely.
But
Californians are not alone, as model predictions show most of the US
coming under an increasing regime of drought as human-caused warming
intensifies throughout the 21st Century. Drought emerging now in the
US Southwest is expected to expand north and eastward, eventually
taking root and reaching an extreme intensity in the Central US. The
front of drought then rides into the US Southeast and Mid-Atlantic
as, by mid-to-late century, it surges northward into Canada.
The
lesson to take from this is that few in the US are spared a fate of
worsening drought spurred by human-caused climate change. And with
climate change clearly linked to the California drought, we may be
getting a bit of the bitter taste of what’s still to come.
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