Using PRISM to Map Extreme Precipitation Events

PRISM (Parameter-elevation Regressions on Independent Slopes Model) is an analytical model that uses point data and a digital elevation model (DEM) to generate gridded estimates of monthly and event-based climatic parameters. Originally developed for precipitation estimation, PRISM has been generalized and applied successfully to temperature, among other parameters. PRISM has been used extensively to map precipitation and minimum and maximum temperature over the United States, Canada, and other countries.

Most of the modeling performed using PRISM has been at time scales of one month or longer. Examples of products already produced include: (1) monthly and annual average climate maps for precipitation, temperature, snowfall, degree days, and other parameters for the 1961-1990 period; and (2) sequential monthly maps for precipitation and temperature (mean maximum and mean minimum) for the period 1895-1993 (one map per month for each year).

Recent work has been conducted using short-term high-intensity precipitation data. Existing products containing maps of precipitation intensity (TP-40, and NOAA Atlas 2, for example) are quite outdated. Successful use of PRISM to model short-term (daily to several days) would suggest that it could be used for assisting in updating of those publications.

Using point data from precipitation stations throughout the Pacific Northwest, PRISM produced several new maps and digital coverages: (1) maps of precipitation for three extreme precipitation-flood events (February and November, 1996, and December-January 1996-97); (2) isopluvial maps for 24-hour precipitation intensities (2-, 25-, and 100-year return periods). The maps have been reviewed by several federal and state agencies and accepted for use in publications describing the flood events, and in landslide assessments conducted by the State of Oregon.

Data are available in several digital formats, including ASCII, GRASS, and Arc/Info, as well as in hard copy.