Stressor-Resource Overlay
Abstract
The Stressor-Resource Overlay method locates watersheds in which relatively high levels of valued resources occur together with relatively high levels of stressors. The method overlaps a map of watershed resources onto a map of watershed stressors. Watersheds with high quality resources and significant stress are noted and considered to be vulnerable.
Method Details
For this analysis, the regional variables are first divided into stressors and resources. Watersheds are scored on the number of stressor variables that fall into the worst 20% of their range and also on the number of resource variables that fall into the best 20% of their range. The overlay map shows watersheds with a significant number of resources and stressors.
The Stressor-Resource Overlay method directly addresses the geographic distribution of vulnerability. A watershed may have many valued resources but still not be vulnerable because it is not experiencing stress. On the other hand, a highly stressed watershed may not be considered vulnerable because its valued resources have already been lost. The most vulnerable watersheds can be considered to be those with intermediate to high levels of stressors together with intermediate to high levels of resources.
Limitations
The Stressor-Resource Overlay does not account for correlation between variables. However, this may not a significant disadvantage. Two stressors may be highly correlated but because of synergistic effects may represent more impact than each stressor independently. Similarly, two resources may be highly correlated but because each is valued in its own right the correlation can be ignored.
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