RPS Methodology, Step 5: Compare Your Watersheds
The screening run results in Step 4 enable you to begin comparing your watersheds in Step 5 and beyond. Again, there is considerable flexibility in how you might use your Recovery Potential Screening (RPS) data to make these comparisons – not only because the Tool has generated four different indices, but also because the three results formats (rank-ordering, three-dimensional bubble plotting and mapping) each tend to reveal strikingly different insights into how your watersheds compare. The purpose of step 5 is to build insights from your screening results through intentionally exploring multiple methods of comparison and visualizing, while not necessarily reaching final watershed selections. As such, you might think of the techniques below as 'discussion support' tools rather than 'decision support' tools - each offers a way to organize complex information, stimulate insights about differences and reveal alternatives for action rather than prescribe a single decision.
Rank-ordering. The simplest of comparison methods, rank-ordering organizes screened watersheds from highest to lowest index scores for each of the four indices. The appeal of rank-ordering is its clarity and simplicity - some watersheds simply score higher than others - which may work well for some users as decision criteria. Rank orders can provide an easy and transparent method to identify a smaller, targeted subset of watersheds, whether by selecting a specific number (e.g., the top 20 watersheds based on RPI score) or a percentage of favorably-ranked watersheds (e.g., the top 5% watersheds from both the Ecological or Social Index results).
The flexibility in rank-ordering is in which scores to use – not only can you choose among the Ecological, Stressor, Social or RPI index results, but watersheds can also be rank-ordered by a single indicator. The RPI score described in step 4 is merely one option, providing a single overall score used to rank-order all the watersheds based on all the indicators measured. It may be just as important to compare rank orders on a purely ecological, stressor or social basis. The limitations of rank-ordering should be noted. Although rank-ordering is useful in distinguishing major differences between high- and low-scoring watersheds, most data likely to be used in a screening probably does not support assuming that very small scoring differences are significant. For example, the 236th-ranked watershed probably is not clearly ‘better’ than the 237th-ranked watershed. Users are advised not to overemphasize the significance of very small rank-order differences. One option for organizing rank-ordered lists in a more generalized ranking is to group them by quantiles, which can be equal-member, equal-value range, or separated by natural breaks in the range of values. More details about using the index and rank-order tables can be found in Using Rank-Ordering in RPS. (4 pp, 741 K)
Bubble plotting. This comparison method was adapted specifically for Recovery Potential Screening as a way to visualize the relative ecological, stressor and social index scores of each watershed at the same time. Bubble plotting visually demonstrates that watershed comparisons are often complex and offers a systematic way to simultaneously observe and consider the relative influence of the three major driving factors on watershed condition and restorability.
Because a bubble plot displays watersheds plotted relative to X (stressor index) and Y (ecological index) axes, with dot size varying with social index score, differences among watersheds are evident by their position on the graph and relative dot size. A second set of axes -- by default, these are set at the median ecological and stressor index values – splits the bubble plot into four quadrants. These quadrants can provide a way to begin sorting and prioritizing watersheds, depending on your screening purpose. For example, the upper left quadrant contains the watersheds that scored higher than the Ecological and lower than the Stressor median scores; these high-Eco, low-Stressor watersheds often contain the healthiest watersheds (good prospects for protection) along with some impaired watersheds that aren’t under severe pressure from stressors (good prospects for restoration). The upper right quadrant, containing high-Eco and high-Stressor watersheds, offers an alternative starting point; these watersheds may contain good candidates for immediate management action because they are at elevated risk from stressors but do not yet display low ecological scores.
Many options for customizing a bubble plot exist in the RPS Tool, such as assigning a color gradient to the bubbles based on one key indicator of interest, or repositioning the median axes to represent user-selected index value thresholds. More details about using bubble plotting can be found in the document Using Bubble Plotting in RPS,(6 pp, 634 K) and within the RPS Tool User Manual.
Mapping recovery potential screening results. Mapping is a universally familiar and popular method for displaying comparative environmental information. Like the other two techniques, mapping has strengths and weaknesses relative to Recovery Potential Screening. For instance, whereas maps are familiar and understandable ways to communicate results to wide audiences, mapping is best at displaying parameters just one at a time.
The variety of available mapping options created in recent years through advances in GIS technology goes far beyond the simplified mapping capabilities in the RPS Tool discussed here. Data tables from the RPS Tool can easily be transformed for use in GIS software when necessary. Because many recovery potential indicators come from GIS data and screening is organized around a data table with each record referenced geographically to a specific water or watershed ID, virtually all of the data outputs from screening can be displayed in map form. Many RPS users, however, do not have fluent GIS skills but can still create, customize and save simple maps from their screening data entirely within the RPS Tool.
- The Tool’s HUC12 MAP tab is initially set to display the watersheds’ RPI score as a light-to-dark color range that corresponds to the high-to-low RPI score gradient, but this is only the default option. Similar maps could be developed for the ecological, stressor or social index scores, or for any single indicator of particular interest (whether used in the screening or not). This type of mapped product can display screening results for the entire assessment area in a way that allows viewers to recognize individual areas they know, while also revealing geographic patterns such as clusters or corridors of good or bad scores. One perspective added by viewing results in map form is the recognition of watersheds in key locations, which if restored could link together larger corridors or patches of other watersheds in better condition. Such maps can be good at stimulating discussions about possible geographically-based strategies in targeting restoration. More details about using mapping can be found in the document Using Mapping in RPS(4 pp, 668 K) , and within the RPS Tool User Manual(53 pp, 31 MB)