Transcript Drought in the Midwest - University of Missouri

Drought in the
Midwest
by
Anthony R. Lupo
Department of Soil, Environmental, and Atmospheric Sciences
302 E ABNR Building
University of Missouri – Columbia
Columbia, MO 65211
Drought in the Midwest
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Why is it important to discuss it?
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Source: NOAA – USDA – Missouri Climate Center
Drought in the Midwest
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Anatomy of a warm, dry summer – 2005
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Let’s look at the mid-western drought of 2005 and
discern the causes
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Spring season (March – May) Avg over mid-MO = 11.6
inches
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Actual rain = 7.3 inches, 63% of normal – this was
typical across the region.
Drought in the Midwest
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It was not particularly warm during the spring,
but the lack of precipitation still leaves the
ground water supplies low!
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A look at the long term record reveals that the
current dryness began in Dec. 2004
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In early June 2005, the rains stopped coming ( at
least less frequently – which is normal).
Drought in the Midwest
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the ground dried out, the temperatures rose,
etc… (“drought begets drought”)
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A “classical” large-scale ridge (drought pattern)
settled over the central USA.
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The following map is the mean conditions from
15 June – 10 August average.
Drought in the Midwest
Drought in the Midwest
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And what was the assessment?
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Summer 2005 - a year to confound
climatologists in the future!
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Why?
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The summer precipitation across the region was
actually above normal!
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Summer precipitation was at 15.3” in midMissouri, normal is 11.7 inches. But 10” of this
occurred during 14 days in August!
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What was the cause?
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A rare case of summer blocking!
Drought in the Midwest
The jet stream was pushed southward – by 10
August.
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By August 13, rains were falling across the
midwest.
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Q: What is blocking?
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A: It is a large-scale, persistent, nearly stationary, midlatitude, dynamically driven ridging in the jet-stream.
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The dynamics of blocking are not completely
understood, even though the climatological behavior is
well-understood (see Lupo and Smith, 1995a,b, Tellus;
Weidenmann et al.m 2002, J. Climate; Burkhardt and
Lupo, 2005, J. of Atms. Sci.)
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Blocking unusual in August, and when they
occur in the Alaska region, they force cooler air
into North America.
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This event was unusual because prolonged
blocking usually CAUSES drought, e.g., Europe
2003, or Alaska, 2004!
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Blocking is one of the keys to understanding
seasonal variations in the weather, both
observed and for predictive purposes. (El Nino
is the other, more later)
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This is well-known in the climatological
community during the winter, but we sometimes
forget about summer season blocking.
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Summer, 2004 – a study in contrast (blocking was
favorable to the mid-west).
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2005
2004
Drought in the Midwest
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Temperatures for Summer 2004 – 3rd coolest summer
on record for mid-MO and a “top 5” for most of the
mid-west and plains. (Source of picture: Midwest
Regional Climate Center)
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June 2004
July 2004
August 2004
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Summer 2004 upper air pattern.
Drought in the Midwest
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Summer 2004 versus Summer 2005 (source
Missouri Agricultural Statistics service)
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2004
2005
Drought in the Midwest
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Soybeans – trend from 1965 – 2005 (source
Missouri Agricultural Statistics service)
Drought in the Midwest
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The impact of El Nino.
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El Nino, what is it?
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El Niño –means literally “the child”, in this case, THE
Child as El Niño typically sets in around Christmas on
the coast of South America!
Drought in the Midwest
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El Niño (or ENSO – El Niño and Southern
Oscillation) is the generic term referring to the
see-saw of warm (El Niño) and cold (La Niña)
sea surface temperature patterns in the eastern
Tropical Pacific
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This occurs every 2 – 7 years!
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El Nino:
Drought in the Midwest
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Currently: (ENSO-neutral) (Source: Climate Prediction
Center)
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Forecasts persist in projecting neutral conditions for the
rest of the year and range from weak La Nina to weak
El Nino conditions
Drought in the Midwest
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Ratley (Ratley, Baxter, Lupo) et al. 2002 discussed the
onset of the summer regime in the mid-west and it’s
relation to ENSO.
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They noticed that before the summer regime becomes
“established”, significant rains (widespread and more
than 0.25 inches) fall on average every 7 days.
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This becomes every 12 days after the onset of the
summer pattern.
Drought in the Midwest
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They then found that in summers involving the
transition into a (future) El Nino situation, the
mean precipitation frequency in spring and
summer is 6 days and 10 days, respectively. (e.g.,
summer 1993, summer 2004)
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For the transition into a La Nina situation, the
corresponding numbers are 8 days, and 19 days,
respectively. (e.g., summer 1983, 1988, 1999,
2005, and historically, the severe dry spell of the
1950’s)
Drought in the Midwest
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Thus, they found that in the Missouri region,
there is not a significant difference region-wide
in precipitation amounts year-to-year, but the
frequency of heavy precipitation is markedly
different.
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It is well-known in the agricultural community
that lighter, more frequent (regular) precipitation
events are much better for crops.
Drought in the Midwest
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The results of Ratley et al. (2002) are based on
30 years worth of data. We’re currently working
on extending this analysis back to 1900.
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Initial results from this extended work (future
Birk and Lupo paper) support the results given
here.
Drought in the Midwest
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What’s in store for 2006?
Drought in the Midwest
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Our group predicted a relatively dry and warm
summer regionally based on a few factors.
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1) For 11 of the past 18 months have had
precipitation amounts below (3) to well-below
normal (8), while only two months have been
very wet.
Drought in the Midwest
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2) During the late winter, early spring, weak La
Nina conditions persisted in the eastern tropical
Pacific. At the time, this was expected to persist
through the spring and summer.
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3) We’ve noticed that we’re in the dry portion of
a long – term cycle. The Missouri Tree Ring
Laboratory bolstered our impressions here.
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4) we’d also projected a drier spring, which did
occur. So far, the summer (June) has also been
in-line with our predictions.
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5) one piece of information arguing against this
forecast is the recent migration of the Pacific
region SSTs back to ENSO-neutral from La
Nina conditions.
Drought in the Midwest
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What is the role of climate and climate change
on drought?
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Let’s look at the decadal record for the USA. We
had drought years in this part of the country
during the 1930s, 1950’s, 1980, 1983, 1988, 1999,
2003, 2005 (but wet years in 1993 and 1995).
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Climate of the USA as measured using
temperature (source National Assessment)
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Borrowed from Karl and Knight (1998), BAMS
Borrowed from Hu et al. (1998), BAMS
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Climate change may impact the temporal and/or
spatial distribution and severity of drought,
however, drought and pluvials (wet spells) will
still occur.
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Let’s look at a couple centuries…….
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Temperatures (source: IPCC)
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•
Borrowed from the Missouri Tree-Ring Laboratory
Palmer Drought Severity Index (PDSI)
8
6
4
2
0
-2
-4
-6
-8
1930
1940
1950
1960
1970
1980
1990
2000
year
• Stambaugh, M.C. and R.P. Guyette. (in prep). 1000 years of
tree-ring reconstructed drought in the Central United States.
Paleoecological understanding
1816, Year without summer
16th Century Megadrought
Maunder Minimum
Medieval Warm Period
Dust Bowl
Little Ice Age
Stambaugh, M.C. and R.P. Guyette. (in prep). 1000 years of tree-ring reconstructed drought
in the Central United States.
Drought in the Midwest
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Borrowed from Fye et al. (2003), BAMS
Drought in the Midwest
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Precipitation in the Northern Plains (Borrowed
from Woodhouse and Overpeck, (1998), BAMS
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Studies have shown that the US climate has been
getting wetter.
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What does the future hold? Model studies have
shown our region may be drier (e.g., IPCC), and
some studies have shown it may be wetter (e.g.
Semenov et al., 2003, Climate Dynamics).
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Many regions of the country give similar mixed
results, but since drought and wet spells are
seasonal in nature (and driven by SST and
atmospheric variations) they will continue to
occur regardless of what the climate does!
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Questions?
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Comments?
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Criticisms?
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[email protected]
Drought in the Midwest
Climate, Climate Change & Hurricanes
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2005 (27)
versus
1933 (21)
Drought in the Midwest
Drought in the Midwest