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Drought in the Midwest

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					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
   Why is it important to discuss it?




   Source: NOAA – USDA – Missouri Climate Center
         Drought in the Midwest
   Anatomy of a warm, dry summer – 2005


   Let’s look at the mid-western drought of 2005 and
    discern the causes

   Spring season (March – May) Avg over mid-MO = 11.6
    inches

   Actual rain = 7.3 inches, 63% of normal – this was
    typical across the region.
         Drought in the Midwest
   It was not particularly warm during the spring,
    but the lack of precipitation still leaves the
    ground water supplies low!

   A look at the long term record reveals that the
    current dryness began in Dec. 2004

   In early June 2005, the rains stopped coming ( at
    least less frequently – which is normal).
         Drought in the Midwest
   the ground dried out, the temperatures rose,
    etc… (“drought begets drought”)

   A “classical” large-scale ridge (drought pattern)
    settled over the central USA.

   The following map is the mean conditions from
    15 June – 10 August average.
Drought in the Midwest
        Drought in the Midwest
   And what was the assessment?
         Drought in the Midwest
   Summer 2005 - a year to confound
    climatologists in the future!

   Why?



   The summer precipitation across the region was
    actually above normal!
         Drought in the Midwest
   Summer precipitation was at 15.3” in mid-
    Missouri, normal is 11.7 inches. But 10” of this
    occurred during 14 days in August!

   What was the cause?



   A rare case of summer blocking!
       Drought in the Midwest
The jet stream was pushed southward – by 10
 August.
         Drought in the Midwest
   By August 13, rains were falling across the
    midwest.
          Drought in the Midwest
   Q: What is blocking?

   A: It is a large-scale, persistent, nearly stationary, mid-
    latitude, dynamically driven ridging in the jet-stream.

   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.)
         Drought in the Midwest
   Blocking unusual in August, and when they
    occur in the Alaska region, they force cooler air
    into North America.

   This event was unusual because prolonged
    blocking usually CAUSES drought, e.g., Europe
    2003, or Alaska, 2004!
         Drought in the Midwest
   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)

   This is well-known in the climatological
    community during the winter, but we sometimes
    forget about summer season blocking.
           Drought in the Midwest
   Summer, 2004 – a study in contrast (blocking was
    favorable to the mid-west).



   2005                         2004
         Drought in the Midwest
   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)
    Drought in the Midwest
   June 2004   July 2004   August 2004
         Drought in the Midwest
   Summer 2004 upper air pattern.
           Drought in the Midwest
   Summer 2004 versus Summer 2005 (source
    Missouri Agricultural Statistics service)



   2004                        2005
        Drought in the Midwest
   Soybeans – trend from 1965 – 2005 (source
    Missouri Agricultural Statistics service)
          Drought in the Midwest
   The impact of El Nino.



   El Nino, what is it?



   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
   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



   This occurs every 2 – 7 years!
        Drought in the Midwest
   El Nino:
          Drought in the Midwest
   Currently: (ENSO-neutral) (Source: Climate Prediction
    Center)




   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
   Ratley (Ratley, Baxter, Lupo) et al. 2002 discussed the
    onset of the summer regime in the mid-west and it’s
    relation to ENSO.

   They noticed that before the summer regime becomes
    “established”, significant rains (widespread and more
    than 0.25 inches) fall on average every 7 days.

   This becomes every 12 days after the onset of the
    summer pattern.
         Drought in the Midwest
   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)

    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
   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.

   It is well-known in the agricultural community
    that lighter, more frequent (regular) precipitation
    events are much better for crops.
         Drought in the Midwest
   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.



   Initial results from this extended work (future
    Birk and Lupo paper) support the results given
    here.
         Drought in the Midwest
   What’s in store for 2006?
         Drought in the Midwest
   Our group predicted a relatively dry and warm
    summer regionally based on a few factors.



   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
   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.


   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.
         Drought in the Midwest
   4) we’d also projected a drier spring, which did
    occur. So far, the summer (June) has also been
    in-line with our predictions.

   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
   What is the role of climate and climate change
    on drought?

   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).
         Drought in the Midwest
   Climate of the USA as measured using
    temperature (source National Assessment)
        Drought in the Midwest
Borrowed from Karl and Knight (1998), BAMS




Borrowed from Hu et al. (1998), BAMS
         Drought in the Midwest

   Climate change may impact the temporal and/or
    spatial distribution and severity of drought,
    however, drought and pluvials (wet spells) will
    still occur.

   Let’s look at a couple centuries…….
        Drought in the Midwest
   Temperatures (source: IPCC)
             Drought in the Midwest
•   Borrowed from the Missouri Tree-Ring Laboratory

                                                       8
                Palmer Drought Severity Index (PDSI)

                                                       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

                                                                                      Dust Bowl
                                                          Maunder Minimum


            Medieval Warm Period                  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
   Borrowed from Fye et al. (2003), BAMS
         Drought in the Midwest
   Precipitation in the Northern Plains (Borrowed
    from Woodhouse and Overpeck, (1998), BAMS
         Drought in the Midwest
   Studies have shown that the US climate has
    been getting wetter.

   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).
         Drought in the Midwest
   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!
         Drought in the Midwest
   Questions?

   Comments?

   Criticisms?

   LupoA@missouri.edu
Drought in the Midwest
Climate, Climate Change & Hurricanes
   2005 (27)   versus   1933 (21)
Drought in the Midwest
Drought in the Midwest

				
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posted:3/1/2012
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