Conditions leading to the extraordinary Summer Heat during
the 1930s US Dust Bowl
Markus G.
1
Donat ,
Andrew D.
1
King ,
Jonathan T.
2
Overpeck ,
Lisa V.
1
Alexander ,
Imke
3
Durre ,
David J.
4
Karoly
1. ARC Centre of Excellence for Climate System Science and Climate Change Research Centre, University of New South Wales, Sydney, Australia; 2. Institute of the Environment, Department of Geosciences and Department of Atmospheric Sciences, University of
Arizona, Tucson, Arizona 85721, USA; 3. NOAA’s National Climatic Data Center, Asheville, NC, USA; 4. School of Earth Sciences and ARC Centre of Excellence for Climate System Science, University of Melbourne, Parkville, Victoria, Australia
Contact: [email protected]
Extreme summer heat during the 1930s
 Large areas of North America were affected by extraordinarily
hot summers during the 1930s
 Observations and 20th Century Reanalysis agree in showing
unprecedented high numbers of hot day frequencies (i.e.
percent of days with T > 90th percentile; TX90p)
 1934 and 1936 stand out as the hottest summers on record –
with higher hot day frequencies than the most recent heat
events in 2011 and 2012
Shifts in the dominating pressure patterns explain
the atmospheric flow anomalies
 Northward extension of the Atlantic Subtropical High and
eastward extension of the Pacific Subtropical High weaken the
moisture transport into the continent
 The 1930s extreme heat and drought was also accompanied by
anomalous warm surface waters in the North Atlantic and
Northeast Pacific oceans
Correlations
Summer heat was accompanied and preceded by
anomalous dry conditions
 Observations and reanalysis show a strong relationship
between summer heat and (meteorological) drought
 The extraordinary hot summers in the 1930s were preceded by
particularly dry spring seasons
 Spring seasons of 2011 and 2012 less dry (although 2012 was
also drier than normal)
Precipitation deficit in spring related to largescale atmospheric flow anomalies
 The Gulf of Mexico is an important moisture source for the
Central US: meridional winds transport warm moist air into the
continent
 There is a strong relationship between weakening/reversal of
the meridional flow and precipitation deficits in the central US
SST (MAMJ)
MSLP (MAMJ)
Precipitation (MAMJ)
Meridional winds 850hPa (MAMJ)
Precipitation and atmospheric flow are related
to large-scale MSLP and SST anomalies
 Spring-time precipitation (left) over the central US and
meridional winds (right) from the Gulf of Mexico into North
America show significant correlations with MSLP and SST
fields
 Correlation patterns are consistent with the anomalies related
to the extreme 1930s heat
Combination of Atlantic and Pacific warm
anomalies leads to dry and hot conditions
 Composites of spring precipitation and summer heat for spring
seasons with warm Pacific SSTs and warm Atlantic SSTs indicate
significantly drier and warmer conditions over the central US
 Multi-linear regression of both Atlantic and Pacific SSTs leads to
even stronger dry and hot anomalies
Warm NE-Pacific
Warm N-Atlantic
Regression
Precipitation (MAMJ) anomaly [mm]
TX90p (JA) anomaly [% of days]
Conclusions
 The hottest summers on record in the central US occurred during the 1930s Dust Bowl
 The extraordinary heat was associated with particularly dry conditions in spring and summer
 Spring drought was related to atmospheric flow anomalies, suppressing the transport of moisture into the
North American continent
 Atmospheric flow anomalies were related to SST warm anomalies during spring over North Atlantic and
Northeast Pacific
→ Potential for predictability of summer heat from spring-time SST and wind anomalies