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Weather and Climate Extremes
John W. Nielsen-Gammon Texas State Climatologist
What’s a Weather or Climate Extreme?
What’s a Weather or Climate Extreme?
• Something unusual • Something high-impact
Why Do People Care About Weather or Climate Extremes?
Why Do People Care About Weather or Climate Extremes?
• Something unusual • Something high-impact
40
-10
40
-10
80
0
1989
80
0
1949
80
0
1930
80
0
1899
40
-10
40
-10
115
90
9.05
Weekly number of flood reports through November
0
5
10
15
20
25
20
25
30
35
15
10 5
0
0
1
World record: 21.93” in 2h 45m, Woodward
Ranch, D’Hanis, Texas
Extreme Weather and Climate Change
The Four Pillars of Attribution of Trends to Climate Change
The greater the number of solid pillars, the greater the scientific confidence that cause and effect has been identified
The Four Pillars
Solid observed
trend
The Four Pillars
Solid observed
trend
Known reason for
change
The Four Pillars
Solid observed
trend
Known reason for
change
Good modeling
ability
The Four Pillars
Solid observed
trend
Known reason for
change
Good modeling
ability
No outside
influences
IPCC SREX
National Centers for Environmental Information
IPCC SREX
National Centers for Environmental Information
IPCC SREX
National Centers for Environmental Information
National Centers for Environmental Information
National Centers for Environmental Information
Climate change turned a 96°F day into a 100°F day
National Centers for Environmental Information
Climate change turned a 96°F day into a 100°F day
Climate change turned a 4°F above normal day into an 8°F above normal day
National Centers for Environmental Information
Climate change turned a 96°F day into a 100°F day
Climate change turned a 4°F above normal day into an 8°F above normal day
Climate change increased the odds of at least 100°F from 1:50 to 1:7
National Centers for Environmental Information
Texas Precip thru 2016: +8.5%
The Four Pillars
Solid observed
trend
Known reason for
change
Good modeling
ability
No outside
influences
✔
Texas Rainfall
Solid observed
trend
Known reason for
change
Good modeling
ability
No outside
influences
✔ ✖
Texas Rainfall
Solid observed
trend
Known reason for
change
Good modeling
ability
No outside
influences
✔ ✖ ✖
Texas Rainfall
Solid observed
trend
Known reason for
change
Good modeling
ability
No outside
influences
✔ ✖ ✖ ✔
Texas Very Heavy Rainfall
Solid observed
trend
Known reason for
change
Good modeling
ability
No outside
influences
✔ ✔ ✔
What makes rainfall different from very heavy rainfall?
IPCC AR5, WG1, Fig. 2.8
56 (50,62)
Tweaked from:
The Faucet
• Warmer air can carry more water = bigger pipe + 7% per °C
• The effect of weather patterns = turning the handle
The Faucet
• The size of the pipe matters most when the faucet is wide open
National Centers for Environmental Information
National Centers for Environmental Information
National Centers for Environmental Information
National Centers for Environmental Information
Statewide Extreme Rainfall Analysis
• For each county & each year: – Find stations with nearly-complete data – Pick the one with longest period of record
• Stitch together daily precipitation into one long time series
• Find events exceeding threshold • Sort chronologically, find date of middle event
Time
Time
Time
Events less frequent Events more frequent
Time
Events less frequent Events more frequent
new frequency old frequency
length of first period length of second period =
*about once every 5000 days
Probable Maximum Precipitation
• The maximum amount of precipitation physically possible for a given basin over a given duration
• Used for critical infrastructure design – Dams – Nuclear power plants
Hurricanes
National Centers for Environmental Information
Problems with Smaller-Scale Extreme Weather Phenomena
• Lack of stability in data record • Low signal-to-noise ratio • No direct information from climate models
National Centers for Environmental Information
Smaller-Scale Extreme Weather Phenomena
Solid observed
trend
Known reason for
change
Good modeling
ability
No outside
influences
✖ ✖ ?
Problems with Smaller-Scale Extreme Weather Phenomena
• Low signal-to-noise ratio – Natural (and random) variability drives
individual events and clusters – Small trends have large monetary impact – Once clear trend is detectable, it’s too late
National Centers for Environmental Information
Hurricanes: The Balance of Evidence
• Increase in peak intensity (1.5 pillars) • Decrease in frequency (1 pillar)
– …but spatially variable (1.5 pillars)
National Centers for Environmental Information
National Centers for Environmental Information
National Centers for Environmental Information
Change in hurricane frequency
National Centers for Environmental Information
Summary
• Extreme weather – Extremely unusual – Extremely impactful
• Texas gets extremes • Climate change affects extremes
– Not always worse – Often very hard to tell
Contact Information
• John W. Nielsen-Gammon • n-g@tamu.edu • 979-862-2248 • http://climatexas.tamu.edu • http://climatechangenationalforum.org • http://www.cpc.ncep.noaa.gov
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