PRISM results have been compared with results for kriging, detrended kriging, and cokriging in
the Willamette River basin, Oregon (Daly et al. 1994). In a jackknife cross-validation exercise, PRISM
exhibited lower overall bias and mean absolute error. PRISM was also applied to northern Oregon and
to the entire western United States. Detrended kriging and cokriging could not be used in these regions
because there was no overall relationship between elevation and precipitation. PRISM’s cross-validation
bias and absolute error in northern Oregon increased a small to moderate amount compared with
those in the Willamette River basin; errors in the western United States showed little further increase.
PRISM has since been applied to the entire United States with excellent results, even in regions where
orographic processes do not dominate precipitation patterns. By relying on many localized, facetspecific
P/E relationships rather than a single domain-wide relationship, PRISM continually adjusts
its frame of reference to accommodate local and regional changes in orographic regime with minimal
loss of predictive capability. Figure 11.4 shows a mapping of the rain shadow effect in Oregon.