Jenny HodbodJason OwensAaron Sidder

The Question

• Is there a correlation between hurricane strength (intensity) and frequency vs. time?

http://www.katrina-hurricane.biz/images/katrina-hurricane-pic3.jpg

Methods

• Analyze the total number of storms per decade

• Analyze the average maximum wind speed per year by decade and the maximum wind speed per decade

• Analyze the number of Category 4 & 5 hurricanes per decade

Chi Squared Tests

• Fo= observed data hurricane data smoothed into decadal averages

• Fe= expected data average for the whole data set

• (fo-fe)^2/fe• Sum of the chi squared values• Compare to the critical chi squared values

Biases and Data Limitations

• Advances in technology from 1850 (pre-Civil War) to 2006

• Limited time frame, no knowledge of historical storm data beyond 1850

• 2005 was a crazy year that skewed the data

Expected and Observed Hurricane Frequencies

Expected and Observed Hurricane Frequencies

y = 2.525x + 63.475

R2 = 0.481

0

20

40

60

80

100

120

1851-1860

1861-1870

1871-1880

1881-1890

1891-1900

1901-1910

1911-1920

1921-1930

1931-1940

1941-1950

1951-1960

1961-1970

1971-1980

1981-1990

1991-2000

2001-2006

decade

Nu

mb

er o

f ev

ents

Line 1

expected frequency

Linear (Line 1)

Chi Squared test: Frequency

• Null Hypothesis= the total number of events is not increasing per decade

• Used the average for the entire data set: fe= 85 events per decade

• 16 df: critical chi squared value at 5% is 26.30

• Chi squared total is 53.02

• Reject null hypothesis

Chi Squared: Frequency cont.fo fe fo-fe fo-fe^2 fo-fe^2/fe

1851-1860 60 85 -25 625 7.35

1861-1870 74 85 -11 121 1.42

1871-1880 75 85 -10 100 1.18

1881-1890 82 85 -3 9 0.11

1891-1900 84 85 -1 1 0.01

1901-1910 79 85 -6 36 0.42

1911-1920 54 85 -31 961 11.31

1921-1930 56 85 -29 841 9.89

1931-1940 104 85 19 361 4.25

1941-1950 98 85 13 169 1.99

1951-1960 98 85 13 169 1.99

1961-1970 98 85 13 169 1.99

1971-1980 98 85 13 169 1.99

1981-1990 95 85 10 100 1.18

1991-2000 109 85 24 576 6.78

2001-2006 95 85 10 100 1.18

53.02

Event Category as a % of Total

0

10

20

30

40

50

60

1851-1860 1861-1870 1871-1880 1881-1890 1891-1900 1901-1910 1911-1920 1921-1930 1931-1940 1941-1950 1951-1960 1961-1970 1971-1980 1981-1990 1991-2000 2001-2006

%

decade

% Tropical Storms

% Category 1

% Category 2

% category 3

% Category 4

% Category 5

Biggest increases are in TS, 4 &5Tropical storms increase (y=1.9985x +17.2)

Category 1 events show a slight increase (y= 0.3029 +16.55)Category 2 events show a decrease (y = -0.775x +20.65)

Category 3 events show a slight increase (y= 0.1191x + 9.425)Category 4 events show an increase (y=0.6162x + 0.575)Category 5 events show an increase (y= 0.3456x-1.125)

Category 4&5 increase

y = 2.301x + 33.75

y = -0.655x + 30.07

y = 0.961x - 0.55

0

10

20

30

40

50

60

70

80

1851-1860 1861-1870 1871-1880 1881-1890 1891-1900 1901-1910 1911-1920 1921-1930 1931-1940 1941-1950 1951-1960 1961-1970 1971-1980 1981-1990 1991-2000 2001-2006

numb

er o

f eve

nts

decade

TS + 1

2+3

4+5

Linear (TS + 1)

Linear (2+3)

Linear (4+5)

TS and Category 1 are increasing2&3 are decreasing4&5 are increasing

Frequency of Category 5 Events

y = 0.345x - 1.125

-2

-1

0

1

2

3

4

5

6

7

1851-1860 1861-1870 1871-1880 1881-1890 1891-1900 1901-1910 1911-1920 1921-1930 1931-1940 1941-1950 1951-1960 1961-1970 1971-1980 1981-1990 1991-2000 2001-2006

Numb

er of

Cate

gory

5 hur

rican

es

Decade

Total Number of Category 5 hurricanes

Category 4&5 increase

• Null hypothesis= category 4 & 5 hurricanes are not increasing in frequency

• Fe= average number of 4&5 per decade= 8

• Total chi squared value= 56.62

• More than the critical chi squared value (26.30)

• Reject the null hypothesis

Maximum Wind Speeds

0

20

40

60

80

100

120

140

160

180

1851-1860 1861-1870 1871-1880 1881-1890 1891-1900 1901-1910 1911-1920 1921-1930 1931-1940 1941-1950 1951-1960 1961-1970 1971-1980 1981-1990 1991-2000 2001-2006

win

d s

pee

d (k

not

s)

decade

Maximum Wind speedaverage maximum wind speed

maximum wind speed

Linear (average maximum wind speed)

Linear (maximum wind speed)

Chi Squared: Wind Speed

• Average the maximum wind speed per year by decade

• Average of these 16 speeds =115 mph (fe)• Null hypothesis= no increase in wind

speed over time• Sum of the chi squared values= 20.02• Below the critical chi squared value for

16df (26.30), therefore accept the null hypothesis

Chi Squared: Wind Speed cont

• Using the maximum wind speed per decade

• Average = 142.5 = fe

• Sum of chi squared values= 29.47

• Reject the null hypothesis at the 5% probability level

Number of Storms Through Time

Who is this?!

Trying to Summon Nikola Tesla?

Number of Storms Through Time

Troughs and Spikes can clearly be seen

Cycles drive our dynamic Planet

Conclusion

Increase in frequency through time? YES

Increase in severity through time? YES

Manifestation of anthropogenicClimate change? ???

Manatees and Hurricanes

Source: WEST INDIAN MANATEE (Trichechus manatus latirostris):FLORIDA STOCKU.S. Fish and Wildlife Service, Jacksonville, Florida; September 2000

Average # of storms by decade as compared to Sea Surface Temp.

Average # of storms by decade as compared to Sea Surface Temp.

• Two-way chi squared test:– SST anomaly and Average # of storms/yr by

decade– Null Hypothesis= no relationship between the

two– Total chi squared value = 29.99– Reject the null hypothesis