Topographic roughness
The influence of earth’s surface features on terrestrial ecosystems can be described at many spatial scales. At planetary and
continental scales, surface roughness influences the location of atmospheric circulation features, temperature variability, rainfall
and runoff patterns; many of the key abiotic components that define ecosystems. Surface roughness also causes patterning in ecosystems
by regulating the distribution of organisms and processes. Topographic roughness is a measure of
variability in the landscape surface and a proxy measure of the potential of disturbances to propagate across the earth’s surface
such as a wildland fire burning across a landscape. We design indices of topographic roughness (top figure) for understanding the dynamics of
fire history as it is controlled by the shape of the land surface. Topographic roughness indices are commonly generated using
trigonometric equations and digital elevation data, however several methods and materials are possible. Components of fire regimes
such as fuels, rate of fire spread, fuel moisture, and weather are strongly influenced by variability in topography.
Our fire history models predict historic mean fire return intervals from indices of topographic roughness and human population variables (bottom figure).
The model demostrates how the relationships between topography, fire, and humans have changed over the last 400 years, a period when fire
predictions can be verified by tree-ring dated fire scars.
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