Drought Through a PRISM: Precipitation Mapping and Analysis Activities at the PRISM Group

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Drought Through a PRISMPrecipitation Mapping
and Analysis Activities at the PRISM Group

• Christopher Daly, Director
• PRISM Group
• Assoc. Prof., Dept. of Geosciences, College of
  Science
• Oregon State University
• Corvallis, Oregon, USA

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• Outline
• Overview of PRISM Group
• Brief introduction to PRISM
• PRISM precipitation products
• Directional precipitation climatologies
• COOP observer bias in daily precipitation
  measurements

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• PRISM Group
• 5-FTE applied research team at Oregon State
  University, funding from contracts and grants
• The PRISM Group is the only center in the world
  dedicated solely to the spatial analysis of
  climate
• PRISM climate mapping technology has been
  continuously developed, and repeatedly
  peer-reviewed, since 1991
• The PRISM Group is the de facto climate mapping
  center for the US
• The PRISM Group is advancing Geospatial
  Climatology as an emerging discipline

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PRISM
Parameter-elevation Regressions on Independent
Slopes Model

• Generates gridded estimates of climatic
  parameters (e.g., P, T, DP)
• Moving-window regression of climate/weather
  values vs. elevation or climatology for each grid
  cell
• Uses nearby station observations
• Spatial climate knowledge base weights stations
  in the regression function by their physiographic
  similarity to the target grid cell

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PRISM

• PRISM spatial climate knowledge base accounts for
  spatial variations in climate due to
• Elevation
• Terrain orientation rain shadows
• Terrain profile terrain enhancement of
  precipitation
• Moisture regime exposure to moisture sources
• Coastal proximity marine air intrusion
• Two-layer atmosphere inversion layer, free
  atmosphere
• Topographic position susceptibility to cold air
  pooling

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PRISM Spatial Climate Datasets
All data sets are state-of-the-art, and are used
as the standard for evaluation of other methods
50 US States Poss.
Mongolia
China
Western Canada
Taiwan
Caribbean Islands
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• Use of PRISM Data Sets
• Official spatial climate data sets of the USDA
• Climate monitoring and projections
• Drought and wildfire studies
• National Weather Service Forecasts
• Weather Channel Forecasts
• Thousands of users, both public and private

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prism.oregonstate.edu

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• PRISM Website

6,000 unique visits per month 3,000 grid
downloads per month 1-2,000,000 hits per year
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CONUS 1895-Present Monthly Climate Time Series

• Tmax, tmin, precip, dew point
• 4-km grid resolution, soon to be 800-m
• At each grid cell, provides realistic historical
  values and variability

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Time Series Data Set Needs Support!
Funding for monthly updates will end in spring
2008 If you use this product, it is time to step
up
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SW flow example January 7, 1990 1200 UTC
NW flow example January 2, 1990 1200 UTC
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SW (Southwesterly) 700-mb flow 1971-2000 mean
annual precipitation
Percent of the domain-wide precipitation
Percent of the normalized all-day mean annual
precipitation
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NW (Northwesterly) 700-mb flow 1971-2000 mean
annual precipitation
Percent of the domain-wide precipitation
Percent of the normalized all-day mean annual
precipitation
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Climo PRISM S (Southerly) 700-mb flow 1971-2000
mean annual precipitation
Percent of the domain-wide precipitation
Percent of the normalized all-day mean annual
precipitation
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• Precipitation Observer Bias
• BAMS June 2007

• The vast majority of United States cooperative
  observers introduce subjective biases into their
  measurements of daily precipitation
• These biases affect the long-term means and
  temporal trends of commonly-used precipitation
  statistics across the country (USHCN included)

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Percent frequency distribution of daily
precipitation gt0.01, 1971-2000
Bishop, CA MAP4.9
Qillayute, WA MAP101.9
Gamma Function
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Percent frequency distribution of daily precip
gt0.01 1971-2000
Philadelphia 1 WSW, MS
Under-reporting bias
nine-phobia
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Percent frequency distribution of daily precip
gt0.01 1971-2000
Cloverdale, OR
5/10 Bias
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Vale s 10-yr Mean Number of Wet Days Dropped
to Half that of Malheur
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Vale s 10-yr Mean Wet Day Precip Increased to
150 that of Malheur
0.22
0.15
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Scope of Observer Bias - USHCN Stations, 1971-2000
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OSU PRISM Group Web Site

• http//prism.oregonstate.edu
• Long-term average climate maps
• Up-to-date monthly maps for CONUS
• Graphics, map server, and data