Before interpreting the Ecological Health Score values, it is important to review the WHAF approach to calculating and scoring ecological health.
What is the range of scores for an index? What do the colors mean?
A health score synthesizes ecological data into a single comparative range of values. Health scores are calculated for all watersheds in Minnesota creating index values from 0 -100, red to green. A score of 100 indicates the best condition or least amount of vulnerability; a score of 0 indicates an unhealthy condition or the highest health vulnerability. The data used for calculating the score must be available for the entire state with data collection likely to continue into the future. Comparing health scores can reveal parts of the ecological system that are functioning well and those that may be facing challenges.
Why are there 'major watershed scores' and 'catchment scores'? What is the difference?
Learn more: What is a watershed?
Major watershed scale ecological health scores
The Watershed Health Assessment Framework was initially developed using Minnesota's 81 major (HUC 8) watersheds as the scale for calculating health scores. Major watersheds organize the landscape into areas that are connected by common hydrologic systems; with land area that slopes toward a common water body such as a major river or lake. This division creates administrative watersheds ranging from 40,000 to 250,000 acres in size. Major watershed boundaries are used by other state agencies such as the Pollution Control Agency (PCA) and the Board of Water and Soil Resources (BWSR) as well as local governments and non-profit agencies.
An example of a health index calculated at the major watershed scale is the Perennial Cover index score. The amount of perennial cover (permanent vegetation) that remains in each major watershed was consistently calculated across the state. At this scale, the results show trends in the statewide pattern, as well as trends within Minnesota's major river basins.
Learn more: What is a watershed?
DNR catchment scale health index scores
Some health index scores use data that can be quantified to a finer spatial scale. The scale selected to "downscale" these indices is the DNR Catchment. There are more than 10,000 catchments within Minnesota and by calculating health scores to this scale, patterns in health emerge that will help manage systems within the boundaries of the major watersheds. The scores also reveal patterns that cross major watershed boundaries that can help inform coordinated management approaches. When available, WHAF Explorer application displays health scores at both scales; major watersheds and DNR catchments. For example, the Perennial Cover index score is also available at the DNR catchment scale.
What’s the hierarchy of Ecological Health Scoring?
Each index score is developed to represent a key ecological process. This is done by using one or more statewide ecological datasets to create a comparative index.
Underneath several of the index scores, there are sub-scores referred to as ‘Sub-Indices'. These scores are on the same 0-100, red to green color ramp, but they represent a subset of data that is related to a specific index score. Index sub-scores are used when multiple related indicators of watershed health are useful to score and present separately. These sub-scores are then combined into a single index score for a more robust representation of watershed health related to a key ecological process. There are four index scores with sub-indices (shown in diagram above).
- Hydrology - Hydrologic Storage
- Biology – Stream Species Quality
- Water Quality – Assessments
- Water Quality – Localized Pollution Sources
If an Index has Sub-Index scores, the Index Score is the mean of the suite of sub-index values.
Together, the multiple index scores that are grouped by component are combined into a Component Score, which is the mean of the corresponding Index Scores. This can be useful for comparative purposes when evaluating which components of watershed health are of greatest concern in a given watershed. These Component Scores are also averaged to create an overall Watershed Health Score to give a single, coarse indicator of a watershed’s relative health.
What are the different types of index scores, and what do they measure?
An individual index score may either broadly quantify a vulnerability to watershed health, or an ecological response to watershed conditions. A watershed vulnerability index will rank the health risk from inherent (natural) landscape condition and/or an introduced (i.e., anthropogenic) condition across Minnesota. A watershed health response index will quantify the relative response emerging from the cumulative effects of watershed stressors.
Description of the broad categories that the various watershed health index scores may represent in terms of ecosystem management.
| SCORE TYPE | INTERPRETATION | EXAMPLE INDEX SCORE |
|---|---|---|
| Vulnerability | What characteristics make the health of my landscape vulnerable? (This can be due to an inherent characteristic and/or as the result of human landscape actions) | Geomorphology – Steep Slopes Near Streams |
| Response | How is my watershed responding to the conditions and risks? (Measures indicate the health status of different ecological communities or density of locations exceeding ecological thresholds) | Biology – Stream Species Quality |
When managing natural resource systems, scientists, land managers and private landowners are often asked to address a problem that is actually a 'system response'. Impaired water quality, flooding, invasive species, poor fishing success - these are all complex responses. While usually measurable, a system response is often not easy to change. Inherent landscape conditions, human alterations and other ecological shifts interact through complex cycles to produce these responses, requiring an in-depth understanding of system function to create a new outcome.
What are the steps for creating a health score?
Fundamental ecological concepts and related processes are the foundation for each health index score. Consistent steps are taken to progress from the identification of an important an ecological concept to the delivery of a health index value.
- Review scientific literature and discuss with subject matter experts to inform selection of significant and well-supported ecological relationships
- Review availability of suitable statewide GIS data to support the selected relationship:
- Temporally stable
- Likely to be repeated
- Consistently collected statewide
- Appropriate resolution for Major Watershed and/or DNR Catchment scale calculations
- Compute results by applying an appropriate GIS method, such as:
- Advanced modeling techniques
- Quantification of comparable values
- Density of features
- Review results, rank and score the range of values
- Set threshold values for scores when available and appropriate
- Assign "0-100" health scores based on the calculated range of values; or based on a range of known ecological conditions