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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

Outline

Meteorological causes of observed changes in heavy precipitation events in the USA.

Changes in extra-tropical cyclones over the Northern Hemisphere.

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.

1010

Seasonal Analysis

1212

Spatial Analysis

1414

Types

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

+0.06 per century

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

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.

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.

NH High-latitude cyclone frequency, normalized by 1959-97 mean & std dev.

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

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.

Questions?

David.Easterling@noaa.gov