Precipitation extremes during 1895 2003 in the continental

Questions • Are the frequency and intensity of extremes changing? • What is the

• Trends in extreme precipitation • Characteristics of early 20 th Century pluvial

U. S. Climate Data • U. S. Cooperative Observer Network in operation since late

Until recently, digital availability of pre-1948 daily climate data has been deficient

Climate Database Modernization Project • U. S. Congress has appropriated funds to NOAA NESDIS

Long-term Stations: 1895 -2003 Red – new; Blue - old

Data Set Quality Control • Basic QC of data performed by National Climatic Data

Extremes Definition • • • Event Duration – days Recurrence (threshold exceedance) –years 1,

1 -dy, 1 -yr Extreme Precipitation: 1895 -1905 Blue = positive anomaly Red =

1 -dy, 1 -yr Extreme Precipitation: 1990 -2000 Blue = positive anomaly Red =

Current Drought in West • High frequencies in western U. S. occurred shortly before

Tree ring reconstruction • Tree-ring reconstruction of western US climate recently extended back to

Western United States Tree-Ring Climate Reconstruction Consecutive Years of Positive Palmer Drought Severity Index

Wettest Seasons in Western U. S. season precipitation (mm) *winter 1908 -09 winter 1968

Causes • Studies with GISS GCM • North Pacific Index • Cyclone tracks Klein,

CONCLUSIONS • Heavy Precipitation Frequencies were highest during the late 20 th Century but

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Precipitation extremes during 1895 -2003 in the continental United States Kenneth E. Kunkel Illinois State Water Survey Collaborators: Dave Easterling, Kelly Redmond, Ken Hubbard, Connie Woodhouse, Ed Cook

Questions • Are the frequency and intensity of extremes changing? • What is the magnitude of natural variability in the frequency and intensity of extremes • What are the implications for the global change debate?

• Trends in extreme precipitation • Characteristics of early 20 th Century pluvial • Causes of observed trends

U. S. Climate Data • U. S. Cooperative Observer Network in operation since late 1880 s • Daily Observations – Max and Min Temp, Precip, Snowfall, Snow Depth • Digitizing of Observations began in 1948 • Miscellaneous projects resulted in the digitizing of selected data prior to 1948

Until recently, digital availability of pre-1948 daily climate data has been deficient

Climate Database Modernization Project • U. S. Congress has appropriated funds to NOAA NESDIS to digitize data records • One of the first data sets chosen for digitization was the daily cooperative records. Digitization of these records finished for the most part in 2001.

Long-term Stations: 1895 -2003 Red – new; Blue - old

Data Set Quality Control • Basic QC of data performed by National Climatic Data Center • A collaborative project, partially funded by NOAA OGP CCDD, to more completely QC these data has been completed • Illinois State Water Survey, National Climatic Data Center (Dave Easterling), U. of Nebraska. Lincoln (Ken Hubbard), Desert Research Institute (Kelly Redmond)

Extremes Definition • • • Event Duration – days Recurrence (threshold exceedance) –years 1, 5, 10, 30 -day duration 1, 5, 20 -year recurrence National index

1 -day duration

1 -dy, 1 -yr Extreme Precipitation: 1895 -1905 Blue = positive anomaly Red = negative anomaly

1 -dy, 1 -yr Extreme Precipitation: 1990 -2000 Blue = positive anomaly Red = negative anomaly

Current Drought in West • High frequencies in western U. S. occurred shortly before 1922 Colorado River compact • Analysis of this period reveals role of extreme seasons • Compact based on 16. 5 maf annual flow; 19062001 average was 15. 1 maf; paleoclimatic reconstructions indicate 400 -year average of only 13. 5 maf

Tree ring reconstruction • Tree-ring reconstruction of western US climate recently extended back to more than 1000 years before present (Cook et al, Science, in press) • Comparative analysis tree-ring reconstruction for early 20 th Century pluvial (consecutive years of positive PDSI, cumulative PDSI sum) – Connie Woodhouse, Dave Easterling, Ed Cook

Western United States Tree-Ring Climate Reconstruction Consecutive Years of Positive Palmer Drought Severity Index # of years period cumulative sum average annual value 9 9 8 7 7 1076 -1084 1112 -1120 1424 -1431 1615 -1621 1911 -1917 12. 86 8. 99 6. 46 11. 51 12. 22 1. 129 1. 000 0. 807 1. 645 1. 750

Wettest Seasons in Western U. S. season precipitation (mm) *winter 1908 -09 winter 1968 -69 winter 1939 -40 spring 1995 *winter 1915 -16 *winter 1913 -14 *winter 1914 -15 winter 1997 -98 winter 1995 -96 *spring 1906 winter 1940 -41 winter 1979 -80 *winter 1910 -11 *winter 1905 -06 winter 1935 -36 209 201 196 189 182 182 181 180 178 177 176 175

Causes • Studies with GISS GCM • North Pacific Index • Cyclone tracks Klein, W. H. , 1957: Principal tracks and mean frequencies of cyclones and anticyclones in the Northern Hemisphere. U. S. Weather Bureau Research Paper 40, 60 pp. U. S. Weather Bureau, Daily Synoptic Series, Historical Weather Maps, Northern Hemisphere Sea Level, January 1899 to June 1939, Cooperative project of U. S. Army Air Force and U. S. Weather Bureau, Washington DC 1944.

CONCLUSIONS • Heavy Precipitation Frequencies were highest during the late 20 th Century but also rather high during the late 19 th and early 20 th Century • The late 20 th Century peak may be caused by Tropical Pacific SST anomalies. The early 20 th Century peak occurs at a time of large positive values of the NPI and above normal frequency of cyclones coming ashore in the Pacific Northwest.

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