Twentieth century trends in dew Twentieth century trends in dew point temperature throughout the point temperature throughout the

Upper MidwestUpper Midwest

Jesse WartmanJesse Wartman

Mentors: Daryl Herzmann and Dr. Eugene TakleMentors: Daryl Herzmann and Dr. Eugene Takle

Why are dew-point Why are dew-point temperatures important?temperatures important?

Important in forecastingUsed for specific and relative humiditiesRegulate transpiration and evaporation processesKey factors in the surface energy and hydrological budgetsWater vapor is the strongest contribution to the greenhouse effect

Past StudiesPast StudiesGaffen and Ross (1999)

Increase through spring and fallRobinson (1998)

Dew points were lower in the Upper Midwest during the winter

Robinson (2000)Increase of 0.9°F per 100 years over U.S.Increase over spring and fall

Possible ErrorsPossible ErrorsNon-uniform stations

Technology and instrument changes

1950s - sling psychrometers1960s – dial hygrothermometersMost recent – HO-83 dial hygrothermometer (NWS)

HypothesesHypothesesDew-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.

Data and MethodsData and MethodsHourly obs through IEM from the NCDC1961-2005MonthlySeasonal

Winter - December, January, & FebruarySpring - March, April & MaySummer - June, July & AugustFall - September, October, & November

YearlyDecadal

Observation StationsObservation StationsLegend of Cities

St. Louis Kansas CityOmahaDes MoinesSioux FallsMinneapolis

Missing DataMissing DataSioux Falls – 0%Minneapolis – 18% - data gap – decadal averages were substituted in, no significant change so left outOmaha – 30.11% - no data before 1974Des Moines – 1.33% - data gapKansas City – 27.27% - no data before 1973St. Louis – 27.27% - no data before 1973

SignificanceSignificanceSignificant if P-value < 0.05Semi-significant if P-value < 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

RESULTSRESULTSMonthly Climatic TrendsSeasonal climatic trends

Yearly average climatic trendsDecadal climatic trendsTwenty-two year climatic

trendsExtreme days

Precipitable water

Monthly Climatic TrendsMonthly Climatic TrendsP-Value < 0.05P-Value < 0.05 – – P-value < 0.1P-value < 0.1

MPLS January Februrary March April May June July August September October Novemeber DecemberSlope 0.083 0.1489 0.0353 0.0439 0.00875 0.02995 0.0415 0.0595 0.051 -0.0156 0.011 0.201P-Value 0.0068 0.0932 0.5524 0.275 0.8698 0.401 0.173 0.0793 0.2325 0.764 0.853 0.0196

STL January Februrary March April May June July August September October Novemeber DecemberSlope 0.185 0.0865 -0.112 0.059 0.041 0.0227 0.0135 0.033 -0.035 0.037 -0.031 0.0084P-Value 0.0358 0.3335 0.1101 0.3046 0.601 0.6276 0.7246 0.462 0.4968 0.5824 0.6948 0.9309

DSM January Februrary March April May June July August September October Novemeber DecemberSlope 0.2199 0.139 0.07 0.053 0.048 0.035 0.07 0.09 0.0139 0.024 0.021 0.094P-Value 0.0025 0.0354 0.127 0.1169 0.342 0.28 0.0043 0.0021 0.691 0.586 0.673 0.1682

FSD January Februrary March April May June July August September October Novemeber DecemberSlope 0.27 0.155 0.0527 0.055 0.061 0.0369 0.086 0.127 0.075 0.0037 0.0265 0.141P-Value 0.0008 0.0272 0.23 0.0891 0.1862 0.306 0.0032 0.0001 0.024 0.9355 0.5542 0.0323

OMA January Februrary March April May June July August September October Novemeber DecemberSlope 0.2597 0.1477 0.0386 0.00191 0.03987 0.0729 0.0858 0.0867 0.0246 0.09 0.0714 0.1234P-Value 0.0155 0.1933 0.609 0.9798 0.603 0.152 0.0503 0.0534 0.666 0.1723 0.404 0.2682

MCI January Februrary March April May June July August September October Novemeber DecemberSlope 0.313 0.178 -0.0215 0.0887 0.0924 0.0828 0.12 0.109 0.0417 0.092 0.092 0.13917P-Value 0.0012 0.076 0.758 0.189 0.2 0.0726 0.0192 0.0087 0.4623 0.189 0.272 0.179

Seasonal Climatic TrendsSeasonal Climatic TrendsWinter Means

0

5

10

15

20

25

30

35

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

Year

Td

(°F)

Seasonal Climatic TrendsSeasonal Climatic TrendsSpring Means

25

30

35

40

45

50

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

Year

Td

(°F)

Seasonal Climatic TrendsSeasonal Climatic TrendsSummer Means

50

52

54

56

58

60

62

64

66

68

70

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

Year

Td

(°F)

Seasonal Climatic TrendsSeasonal Climatic TrendsFall Means

25

30

35

40

45

50

55

1961

1963

1965

1967

1969

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

Year

Td

(°F)

Yearly Average Climatic TrendsYearly Average Climatic Trends

29

33

37

41

45

49

1961 1967 1973 1979 1985 1991 1997 2003

Year

Td

(°F)

Yearly Climatic TrendsYearly Climatic TrendsAverages

Kansas City: .128*Sioux Falls: .1*Minneapolis: .083*Des Moines: .077*Omaha: .064St. Louis: .0084

Total ~ 7.54°F per 100 years0.9°F per 100 years (Robinson, 2000)

Decadal Climatic TrendsDecadal Climatic TrendsYearly Trend 1961-1970

30

32

34

36

38

40

1961 1962 1963 1964 1965 1966 1967 1968 1969 1970

Year

Yearly Trend 1971-1980

28

30

32

34

36

38

40

42

44

46

48

50

1971 1972 1973 1974 1975 1976 1977 1978 1979 1980

Year

Td

(°F)

Td

(°F)

Decadal Climatic TrendsDecadal Climatic TrendsYearly Trends 1981-1990

3032343638404244464850

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990

Year

Yearly Trend 1991-2000

3032343638404244464850

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

Year

Td

(°F)

Td

(°F)

Twenty-two year trends1961-1983

Omaha: -64°F *St. Louis: -13°FDes Moines: -5 °FMinneapolis: -4°FKansas City: -3°FSioux Falls: 4°F

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

Twenty-two year trends

-70-60-50-40-30-20-10

01020

OMA STL DSM MSP MCI FSD

1961-19831984-2005

Pacific Decadal Oscillation (PDO)

Monthlytemperature

anomaly (°C)

4

2

0

-2

-4

Years

Monthly values for the PDO index (Jan. 1955-Oct. 2006) (Mantua, 2000)

Extreme days: dew points over Extreme days: dew points over 70°F70°F

0

10

20

30

40

50

60

DSM STL (1973-2005) MSP FSD OMA (1974-2005) MCI (1973-2005)

Extreme days: dew points over Extreme days: dew points over 75°F75°F

0

5

10

15

20

25

DSM STL (1973-2005) MSP FSD OMA (1974-2005) MCI (1973-2005)

Precipitable WaterPrecipitable WaterSurface Vapor Pressure: Po = 1mb*e {1.81+(17.27*D)/(D+237.3)}

Precipitable Water: h = Po /(ρw*g)

Precipitable WaterPrecipitable Water

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Precipitable Water (mm/100 years)

FSD

MSP

OMA

DSM

MCI

STL

Citie

s .

Winter

Summer

Year Mean

ImplicationsImplications

ImplicationsImplicationsPrecipitationHeat stressCrop productionSoil errosionWater suppliesHuman healthHeat waves

Concluding RemarksConcluding RemarksShift from negative trend to positive trendPositive overall trendHypotheses

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

7.54°F over 100 years in Upper Midwest0.9°F over 100 years in United States

Future WorkFuture WorkModelling studies

Future increases?Increase in greenhouse gasesPDOEl NiñoAtlantic OscillationOther factors

AcknowledgementsAcknowledgementsDaryl E. HerzmannEugene S. TakleJon Hobbs

Questions?Questions?jwartman@iastate.eduhttp://www.meteor.iastate.edu/~jwartman/portfolio/project.html