NCDC: Climate of 2002 - August

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Climate of 2002 - August
Oregon Drought

National Climatic Data Center, 13 September 2002

Statewide Overview / Eastern Oregon Paleo Perspective

Statewide Overview

August marked the seventh consecutive month with near to below-normal precipitation on a statewide basis, resulting in the seventh driest May-August and February-August on record (see table below). The extreme dry conditions of the previous wet season, however, when combined with the moderately dry wet season of this year put much of the state in the extreme drought category (based on the Palmer Hydrological Drought Index and the 24-month Standardized Precipitation Index).

As a result, agriculture has suffered, reservoirs have been depleted (map provided by U.S. Bureau of Reclamation, and several wildfires have burned across the state.

According to the NIFC, the Florence Fire and Sour Biscuit Fire merged on August 7, becoming the largest fire in Oregon's history burning over 500,000 acres (200,000 hectares) by the end of the month.
Pictures provided by Western Regional Climate Center climatologist, Dr. Kelly Redmond, revealed grass growing on the bottom of Antelope Reservoir. This reservoir, which is in the far southeastern corner of Oregon, would normally have water, but it has been basically empty (or low) for quite some time.

Statewide Precipitation Ranks
for Oregon , 2001-2002
Period	Rank
Aug	16^th driest
Jul-Aug	14^th driest
Jun-Aug	21^st driest
May-Aug	7^th driest
Apr-Aug	17^th driest
Mar-Aug	14^th driest
Feb-Aug	7^th driest
Jan-Aug	16^th driest
Dec-Aug	27^th driest
Nov-Aug	34^th driest
Oct-Aug	34^th driest
Sep-Aug	28^th driest

Click here for graphic showing Oregon statewide precipitation departures, January 1998 - present

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Click here for graphic showing Oregon statewide Palmer Z Index, January 1998 - present

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Click here for graphic showing Oregon statewide precipitation, Feb-August 1895-2002

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Click here for graphic showing Oregon statewide Palmer Hydrological Drought Index, January 1900 - August 2002

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Eastern Oregon Paleoclimate Perspective

Palmer Drought Indices based on instrumental (rain gauge and thermometer) observations go back to the beginning of the 20th century. To get an idea of the drought history of a region prior to January 1900, we must rely on paleoclimatic data such as tree rings. The graph to the right shows the August Palmer Drought Severity Index (PDSI) reconstructed from tree-rings in eastern Oregon going back to 1706. The blue curve shows the PDSI computed from weather observations for 1900-2002, and the red curve shows the tree-ring reconstruction for 1706-1978. The thin curves are annual values and the thick curves are ten-year moving averages. (The tree-ring data were contributed by Garfin and Hughes, 1996; a description of the data is available at the NOAA Paleoclimatology web site; the data are also available from the web site.)

Click here for graphic showing eastern Oregon Palmer Drought Severity Index, August, 1706-2002

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The tree rings reproduce a conservative PDSI (the extremes are not reproduced exactly, but the overall pattern and trend are reproduced well). The drought of the 1920s-1930s is captured well in both the instrumental and reconstructed indices and represents the most severe drought episode in this region based on this data. A drought episode similar in magnitude and duration occurred about a hundred years earlier.

References:

Garfin, G.M. and M.K. Hughes, 1996. "Eastern Oregon Divisional Precipitation and Palmer Drought Severity Index from Tree-Rings." Report to the U.S. Forest Service Intermountain Research Station. USDA Forest Service Cooperative Agreement PNW 90-174.

NCDC / Clim. Monitoring / Climate-2002 / Aug / U.S. Regional Drought / Search / Help

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