Observed Changes in Heavy Precipitation
Events and Extratropical Cyclones
David R. Easterling1, Kenneth E. Kunkel2,
David Kristovitch3, Scott Applequist1, Leslie Stoecker3,
Byron Gleason1, Rebecca Smith4
1NOAA/National
Climatic Data Center, Asheville, NC
2CICS/NOAA/National Climatic Data Center, Asheville, NC
3Illinois State Water Survey, Champaign, IL
4Colorado State University, Ft. Collins, CO
Supported by the NOAA Climate Program Office
1
Outline
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
Meteorological causes of observed
changes in heavy precipitation events
in the USA.
Changes in extra-tropical cyclones
over the Northern Hemisphere.
1.8
Annual
1.6
+21% per Century
Frequency Index
1.4
1.2
1.0
0.8
0.6
0.4
1890
1910
1930
1950
1970
1990
2010
Year
Updated from Kunkel, K. E., D.R. Easterling, K. Redmond, and K. Hubbard, 2003: Temporal variations of extreme
precipitation events in the United States: 1895–2000, Geophys. Res. Lett., 30, 1900, 10.1029/2003GL018052
What’s Causing The Increase?



Have there been secular changes in
the frequency, intensity, and other
characteristics of the meteorological
phenomena producing heavy
precipitation?
Are the recent increases primarily a
result of increases in atmospheric
water vapor concentrations?
Or some combination of the above?
U.S. Climate Data


U.S. Cooperative Observer Network in
operation since late 1880s, used 935
long-term stations.
Daily Observations – Max and Min
Temperature, Precipitation, Snowfall,
Snow Depth
Long-term Precipitation Stations
Extremes Definition



Event Duration – days
Recurrence (threshold exceedance) –
years
1-day duration, 5-year recurrence
Meteorological Types

Extratropical Cyclones
−
−





Frontal (at least ~300 km away from center
of surface or upper low)
ETC (near surface or upper low center)
Tropical Cyclones
Mesoscale Convective Systems
Air Mass Convection
Southwest Monsoon
Upslope
Data Sources For Synoptic Types





Reanalysis pressure and temperature
Tropical Cyclone tracks
Surface fields of temperature and
precipitation
Daily weather maps
Identification of types mostly based
on judgment of authors.
Seasonal Analysis
10
1.2
1.0
June-October
+20% per Century
Frequency Index
0.8
0.6
0.4
0.2
0.0
1890
1910
1930
1950
Year
1970
1990
2010
Spatial Analysis
12
Types
14
Frontal, ETC & Tropical Events
Number of Heavy Events/Station
0.20
0.16
0.12
0.08
0.04
0.00
1900
1910
1920
1930
1940
1950
1960
1970
Year
ETC
Frontal
Tropical
1980
1990
2000
2010
Other Events
Number of Heavy Events/Station
0.04
0.03
0.02
0.01
0.00
1900
1910
1920
1930
1940
1950
1960
1970
Year
Monsoon
Air Mass
MCC
Upslope
1980
1990
2000
2010
Contribution of Tropical
Cyclones
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
HURDAT tropical cyclone tracks
dataset
Heavy precipitation event considered
to be caused by tropical cyclone if it
occurred within 5 degrees of track
Heavy Precipitation Event Index
Tropical Cylone Events
0.3
0.2
Appalachians
+0.06 per
century
0.1
Carolina Coast
Florida
Gulf Coast
New England
Southeast Inland
0.0
1895- 1901- 1911- 1921- 1931- 1941- 1951- 1961- 1971- 1981- 1991- 20011900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2008
Year
Carolina Coast
Heavy Precipitation Event Index
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1895
1905
1915
1925
1935
1945
1955
Year
1965
1975
1985
1995
2005
Southeast
Number of Heavy Events/Station
0.20
Frontal
0.15
0.10
TC
0.05
0.00
19091910
19111920
19211930
19311940
19411950
19511960
19611970
19711980
19811990
19912000
20012006
Decade
ETC
Frontal
Monsoon
Air Mass
MCC
Upslope
TC
Extra-tropical Cyclones: have ETC
tracks shifted and have they
become more intense?
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Use the 100+ year Historical Reanalysis being run by NOAA/Earth
System Research Lab.
Sea-level pressure, 2o grid, 6h, 56
ensemble members
ETCs defined as local minimum,
surrounded by +2 hPa contour.
NH Mid-latitude cyclone frequency, normalized by 1959-97 mean & std dev.
McCabe, G. J., M. P. Clark, and M. C. Serreze,
2001: Trends in Northern Hemisphere
surface cyclone frequency and intensity.
Journal of Climate, 14, 2763-2768.
Tracked ETC counts for winter
season (Nov-Mar) ending in
the year indicated.
NH High-latitude cyclone frequency, normalized by 1959-97 mean & std dev.
CONCLUSIONS
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The observed national upward trend in
heavy precipitation frequency is due
primarily to trends during June through
October
Statistically significant upward trends in
the # of events caused by frontal systems
and tropical cyclones
Upward trends in tropical cyclone events
in all Atlantic and Gulf regions except for
Florida
Extratropical Cyclones
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Results from NOAA Historical
Reanalysis compare well with previous
analyses for post 1950 period.
If pre-1950 period included relative
increase from 1900-1950 for midlatitudes, relative decline from 1920s
for high latitudes.
Questions?
David.Easterling@noaa.gov