jenny hodbod jason owens aaron sidder. the question is there a correlation between hurricane...
Post on 19-Dec-2015
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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
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