Drought Through a PRISM: Precipitation 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

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

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

-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 PRISM Parameter-elevation Regressions on Independent Slopes Model

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 PRISM

PRISM Spatial Climate Datasets Western Canada China Taiwan Mongolia Caribbean Islands All data sets are state-of-the-art, and are used as the standard for evaluation of other methods 50 US States & Poss.

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

prism.oregonstate.edu

PRISM Website ~6,000 unique visits per month ~3,000 grid downloads per month ~1-2,000,000 hits per year

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

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

NW flow example: January 2, UTC SW flow example: January 7, UTC

Percent of the normalized all-day mean annual precipitation SW (Southwesterly) 700-mb flow mean annual precipitation Percent of the domain-wide precipitation

Percent of the normalized all-day mean annual precipitation NW (Northwesterly) 700-mb flow mean annual precipitation Percent of the domain-wide precipitation

Percent of the normalized all-day mean annual precipitation Climo PRISM S (Southerly) 700-mb flow mean annual precipitation Percent of the domain-wide precipitation

Precipitation Observer Bias Precipitation Observer Bias [BAMS June 2007] Precipitation Observer Bias Precipitation Observer Bias [BAMS June 2007] The vast majority of United States cooperative observers introduce subjective biases into their measurements of daily precipitationThe 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)

Percent frequency distribution of daily precipitation >=0.01”, Bishop, CA MAP=4.9” Bishop, CA MAP=4.9” Qillayute, WA MAP=101.9” Qillayute, WA MAP=101.9” Gamma Function

Percent frequency distribution of daily precip >=0.01” Philadelphia 1 WSW, MS Under-reporting bias nine-phobia

Cloverdale, OR 5/10 Bias Percent frequency distribution of daily precip >=0.01”

Vale ‘s 10-yr Mean Number of Wet Days Dropped to Half that of Malheur 25% 13%

Vale ‘s 10-yr Mean Wet Day Precip Increased to 150% that of Malheur

Scope of Observer Bias - USHCN Stations,

OSU PRISM Group Web Site Long-term average climate maps Up-to-date monthly maps for CONUS Graphics, map server, and data