1 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 2 CICS/NOAA/National Climatic Data Center, Asheville, NC 3 Illinois State Water Survey, Champaign, IL 4 Colorado 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, /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.

10 Seasonal Analysis

12 Spatial Analysis

14 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

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, 2 o 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, NH Mid-latitude cyclone frequency, normalized by mean & std dev. Tracked ETC counts for winter season (Nov-Mar) ending in the year indicated.

NH High-latitude cyclone frequency, normalized by 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 for mid- latitudes, relative decline from 1920s for high latitudes.

Questions?