Climate zone delineation: evaluating approaches for use in natural resource management

Recent efforts by the United States Department of the Interior (DOI) have the potential to make climate zones the basic geographic units guiding monitoring and resource management programs in the western U.S. We evaluated a new National Park Service approach for delineating climate zones that will likely be a model for other DOI agencies. Using the test case of the Greater Yellowstone Area in Wyoming, Montana and Idaho, we conducted three separate analyses, each based on a different dataset. Cluster analysis of 1971-2000 temperature and precipitation normals grouped weather stations according to similarities in seasonal patterns. Principal Components Analysis (PCAs) of 1895-2008 monthly data grouped stations by similarities in long-term variability. Finally, an analysis of snow data further subdivided the zones defined by the other two analyses. The climate zones produced by the cluster analysis and the PCAs were roughly similar to each other, but the differences were significant. The two sets of zones may be useful for different applications. For example, studies that analyze links between climate patterns and the demography of threatened species should focus on the results of the PCAs. The broad similarity among results produced by the different approaches supported the application of these zones in climate-related monitoring and analysis. However, since choices in data and methodology can affect the details of maps depicting zone boundaries, there are practical limitations to their use.