Including the freshwater landscape in a multi-themed regionalization system to capture macroscale patterns
Results/Conclusions: Using principal components analysis as a variable reduction approach, we found that 17, 10, and 24 PCA axes were needed to capture 85% of the variation in the natural (a) terrestrial landscape, (b) freshwater landscape, and (c) integrated landscape, respectively. Using these PCA axes, we clustered USGS 12-digit hydrologic units to make contiguous regions for each of the three regionalizations. We did not assume an optimum number or size of region. Instead, we used an iterative process, and varied the number of regions from 5-1000 in order to maximize within-region similarity in landscape features. For each of the three regionalizations, 100 was identified as the optimal number of regions. This optimal number was based on comparing fitted curves of the within-region sum of squares error as region number increased to that from contiguous regions made using random start seeds. The region boundaries from the natural freshwater and natural terrestrial regionalizations differed greatly, with the integrated freshwater and terrestrial landscape most closely resembling the natural freshwater landscape.This result points to the importance of including the freshwater landscape in regionalization efforts, as well as how a multi-themed regionalization system that includes the freshwater landscape can capture dominant macroscale patterns.