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