Observed Changes in Heavy Precipitation Events and Extratropical Cyclones
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Observed Changes in Heavy Precipitation Events and Extratropical
CyclonesDavid R. Easterling1, Kenneth E. Kunkel2,
David Kristovitch3, Scott Applequist1, Leslie Stoecker3, Byron Gleason1, Rebecca Smith4
1NOAA/National Climatic Data Center, Asheville, NC2CICS/NOAA/National Climatic Data Center, Asheville, NC3Illinois State Water Survey, Champaign, IL4Colorado State University, Ft. Collins, CO
Supported by the NOAA Climate Program Office
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Outline
Meteorological causes of observed changes in heavy precipitation events in the USA.
Changes in extra-tropical cyclones over the Northern Hemisphere.
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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
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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?
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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
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Long-term Precipitation Stations
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Extremes Definition
Event Duration – days Recurrence (threshold exceedance) –
years 1-day duration, 5-year recurrence
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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
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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.
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Seasonal Analysis
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Spatial Analysis
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Types
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Contribution of Tropical Cyclones
HURDAT tropical cyclone tracks dataset
Heavy precipitation event considered to be caused by tropical cyclone if it occurred within 5 degrees of track
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+0.06 per century
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Southeast
0.00
0.05
0.10
0.15
0.20
1909-1910
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 H
eavy
Eve
nts
/Sta
tio
n
ETC Frontal Monsoon Air Mass MCC Upslope TC
Frontal
TC
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Extra-tropical Cyclones: have ETC tracks shifted and have they become more intense?
Use the 100+ year Historical Re-analysis 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.
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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.
NH Mid-latitude cyclone frequency, normalized by 1959-97 mean & std dev.
Tracked ETC counts for winter season (Nov-Mar)
ending in the year indicated.
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NH High-latitude cyclone frequency, normalized by 1959-97 mean & std dev.
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CONCLUSIONS
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
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Extratropical Cyclones
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 mid-latitudes, relative decline from 1920s for high latitudes.