Twentieth century trends in dew point temperature throughout the Upper Midwest

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Twentieth century trends in dew point temperature
throughout the Upper Midwest

• Jesse Wartman

Mentors Daryl Herzmann and Dr. Eugene Takle
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Why are dew-point temperatures important?

• Important in forecasting
• Used for specific and relative humidities
• Regulate transpiration and evaporation processes
• Key factors in the surface energy and
  hydrological budgets
• Water vapor is the strongest contribution to the
  greenhouse effect

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Past Studies

• Gaffen and Ross (1999)
• Increase through spring and fall
• Robinson (1998)
• Dew points were lower in the Upper Midwest during
  the winter
• Robinson (2000)
• Increase of 0.9F per 100 years over U.S.
• Increase over spring and fall

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Possible Errors

• Non-uniform stations
• Technology and instrument changes
• 1950s - sling psychrometers
• 1960s dial hygrothermometers
• Most recent HO-83 dial hygrothermometer (NWS)

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Hypotheses

• Dew-point temperatures have experienced
  significant, positive trends over the past 44
  years in the Upper Midwest.
• Those dew-point temperature tendencies are no
  different from trends that have been found across
  the rest of the United States in past studies.

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Data and Methods

• Hourly obs through IEM from the NCDC
• 1961-2005
• Monthly
• Seasonal
• Winter - December, January, February
• Spring - March, April May
• Summer - June, July August
• Fall - September, October, November
• Yearly
• Decadal

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Observation Stations

• Legend of Cities
• St. Louis
• Kansas City
• Omaha
• Des Moines
• Sioux Falls
• Minneapolis

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Missing Data

• Sioux Falls 0
• Minneapolis 18 - data gap decadal averages
  were substituted in, no significant change so
  left out
• Omaha 30.11 - no data before 1974
• Des Moines 1.33 - data gap
• Kansas City 27.27 - no data before 1973
• St. Louis 27.27 - no data before 1973

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Significance

• Significant if P-value lt 0.05
• Semi-significant if P-value lt 0.1
• P-Value calculated in JMP, observed
  significance probability from t-ratios
• T-ratio tests hypothesis that each parameter is
  zero, ratio of the parameter estimate to its
  standard error

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• RESULTS
• Monthly Climatic Trends
• Seasonal climatic trends
• Yearly average climatic trends
• Decadal climatic trends
• Twenty-two year climatic trends
• Extreme days
• Precipitable water

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Monthly Climatic TrendsP-Value lt 0.05 P-value
lt 0.1
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Seasonal Climatic Trends
Td (F)
13
Seasonal Climatic Trends
Td (F)
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Seasonal Climatic Trends
Td (F)
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Seasonal Climatic Trends
Td (F)
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Yearly Average Climatic Trends
Td (F)
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Yearly Climatic Trends

• Averages
• Kansas City .128
• Sioux Falls .1
• Minneapolis .083
• Des Moines .077
• Omaha .064
• St. Louis .0084
• Total 7.54F per 100 years
• 0.9F per 100 years (Robinson, 2000)

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Decadal Climatic Trends
Td (F)
Td (F)
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Decadal Climatic Trends
Td (F)
Td (F)
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Twenty-two year trends

• 1961-1983
• Omaha -64F
• St. Louis -13F
• Des Moines -5 F
• Minneapolis -4F
• Kansas City -3F
• Sioux Falls 4F

• 1984-2005
• Omaha 12F
• St. Louis 13F
• Des Moines 11F
• Minneapolis 13F
• Kansas City 14F
• Sioux Falls 11F

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Twenty-two year trends
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Pacific Decadal Oscillation (PDO)
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Extreme days dew points over 70F
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Extreme days dew points over 75F
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Precipitable Water

• Surface Vapor Pressure
• Po 1mbe 1.81(17.27D)/(D237.3)
• Precipitable Water
• h Po /(?wg)

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Precipitable Water
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Implications
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Implications

• Precipitation
• Heat stress
• Crop production
• Soil errosion
• Water supplies
• Human health
• Heat waves

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Concluding Remarks

• Shift from negative trend to positive trend
• Positive overall trend
• Hypotheses
• Dew-point temperatures have experienced
  significant, positive trends over the past 44
  years in the Upper Midwest. -gt TRUE
• Those dew-point temperature tendencies are no
  different from trends that have been found across
  the rest of the United States in past studies. -gt
  FALSE
• 7.54F over 100 years in Upper Midwest
• 0.9F over 100 years in United States

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Future Work

• Modelling studies
• Future increases?
• Increase in greenhouse gases
• PDO
• El Niño
• Atlantic Oscillation
• Other factors

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Acknowledgements

• Daryl E. Herzmann
• Eugene S. Takle
• Jon Hobbs

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Questions?

• jwartman_at_iastate.edu
• http//www.meteor.iastate.edu/jwartman/portfolio/
  project.html