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Observed Changes in Heavy Precipitation Events and Extratropical Cyclones

Observed Changes in Heavy Precipitation Events and Extratropical Cyclones. David R. Easterling 1 , Kenneth E. Kunkel 2 , David Kristovitch 3 , Scott Applequist 1 , Leslie Stoecker 3 , Byron Gleason 1 , Rebecca Smith 4 1 NOAA/National Climatic Data Center, Asheville, NC

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Observed Changes in Heavy Precipitation Events and Extratropical Cyclones

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  1. 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

  2. Outline Meteorological causes of observed changes in heavy precipitation events in the USA. Changes in extra-tropical cyclones over the Northern Hemisphere.

  3. 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

  4. 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?

  5. 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

  6. Long-term Precipitation Stations

  7. Extremes Definition • Event Duration – days • Recurrence (threshold exceedance) –years • 1-day duration, 5-year recurrence

  8. 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

  9. 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.

  10. Seasonal Analysis

  11. Spatial Analysis

  12. Types

  13. 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

  14. +0.06 per century

  15. Frontal TC

  16. 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.

  17. 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. 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.

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

  19. 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

  20. 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.

  21. Questions? David.Easterling@noaa.gov

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