*Topo-Climatic Variability*

Natural communities occur across a range of both macro and micro-climates. For example, some major temperate grassland types of the Western Great Plains form the upland 'matrix' of an ecoregion and in topography of limited relief, while other woodland types occur in microclimates formed by rugged canyons and low mountain ranges. Their current distributions are largely based on both regional and local-scale responses to temperature and precipitation. The relative variability in climate encompassed by the distribution of a given community can provide another useful indication of adaptive capacity under changing climate [72]. The idea of climate change 'velocity' [73] has been proposed as a measure of climate change exposure, and it captures in part the interaction of changing climate with topography. The measure is derived by dividing the rate of projected climate change in units of ◦C per year by the rate of spatial climate variability, i.e., the temperature di fferential of adjacent grid cells, measured in ◦C km−1. Areas with relatively rugged topography and elevational gradients will support a greater diversity of microclimate conditions (re: low velocity) as compared with areas of flat topography. Therefore, for the same increment of climate change and time-period, a given species would be required to migrate a shorter distance in areas of rugged topography as compared with expansive flat landscapes.

Since we provide for independent measures of climate change exposure with the HCCVI framework, we used maps of terrain ruggedness to express the influence of topography on microclimate variability. The terrain ruggedness index (TRI) provided by Riley et al. [74] was used with 90 m digital elevation data of North America. TRI is the sum change in elevation between a given grid cell and its eight neighboring grid cells. For example, a cell located at 200 m elevation, surrounded by four cells at 100 m and four more cells at 125 m would yield a TRI of 700 (400 + 500 − 200 = 700). The topo-climatic variability map was derived by normalizing TRI scores to the 0.01–1.0 scale using extreme TRI estimates as projected for North America (TRI = 6196). We overlaid this normalized map with distributions of each vegetation type to arrive at per pixel scores and then summarized them by 100 km<sup>2</sup> hexagon.

#### **Appendix B. Proportional Area for All Component and Composite HCCVI Scores for 52 Major Vegetation Types (***Supplied as Separate File***)**

Again, the summarized results for overall climate change vulnerability of the 52 assessed types are found in Appendix B. Type-specific map, text, and tabular summary information is accessible within Supplementary Materials (see: https://databasin.org/galleries/6704179ca499490bafd2e9080df1908a).
