Delineation of climatic regions in Maine

As part of a project to develop a productivity-oriented site classification system for spruce and fir in Maine, multivariate analyses of meteorological data were used to partition the state into homogeneous climatic zones. Data were obtained for 63 weather stations reporting both temperature and precipitation in Maine during the period 1954–1983. Monthly means were computed for each variable over the period of record and summarized by four 3-month seasons. Eighty-two percent of the variation in the 37 variables was accounted for by the first three principal components. Cluster analysis identified eight homogeneous groups of weather stations. Results from the principal components analysis were spatially extrapolated across the state using stepwise regression to define the relationship between the first two principal components and the location variables latitude, longitude, and elevation. Principal component scores were predicted across the state along a grid composed of township line intersections. The Triangulated Irregular Network of ARCINFO, a geographic information system software package, was used to spatially summarize the predicted component scores into climagraphic maps. The combined results from cluster analysis and spatial extrapolation of the principal components analysis suggested the presence of four broad climatic regions, which were further subdivided into nine climatic zones. Overlap among the four regions and nine zones was evaluated with a jackknifed classification of a linear discriminant function. Ninety-four percent of the weather stations were correctly classified by climatic region, whereas 76% were correctly classified by climatic zone. The high degree of correspondence between climatic zones and biophysical regions reinforced results of the multivariate analyses.