What does the overall combined watershed health score reveal about patterns of watershed health across the state of Minnesota?
Watershed Health Score in the WHAF Explorer
Why is this important for understanding Watershed Health?
The Watershed Health Score combines the five component health scores into an overall average score for each major watershed. Each of the five components has an equal influence on the combined Watershed Health Score. Although combining all the scores will mask extreme values from any individual index, the overall Watershed Health Score is a useful indicator to broadly compare watershed health across the state. The overall score can be used to guide an exploration of the relative influence of scores for each underlying component. The Watershed Health Score is updated in response to updates in any of the underlying health scores within the suite of health scores.
As a general pattern, Watershed Health Scores for major watersheds in Minnesota show lower scores in the southern and western parts of the state, with the lowest scores in the Red River and Minnesota River basins. These overall Watershed Health Scores closely follow landscape alterations that removed permanent vegetation, altered streams and wetlands, or increased impervious surface.
Creating the index
Input data
MN Geospatial Commons Data: Watershed Health Assessment Framework Health Scores.
Calculating the index
The Watershed Health Score is the average of the five Component Health Scores. The component scores are only calculated at the major watershed scale, and each component score has an equal influence on the final combined Watershed Health Score.
(Hydrology Score + Biology Score + Connectivity Score + Geomorphology Score + Water Quality Score)/5
Index results
Interpretation of results
Although the Watershed Health Score masks extreme values from individual indices, it can be useful for broad comparisons of watershed health. Adding other boundaries such as Major River Basins and Ecological Classification Boundaries reveals important patterns of health for related watersheds, such as those within the same major river basin, or within the same Ecological Classification. Relationships between landscape conditions, river basin position, and watershed health begin to emerge. For example, an upstream to downstream decrease in health scores is evident in the Upper Mississippi River Basin. Further exploration would be needed to determine which health stressors accumulate as the river moves downstream, and which health challenges are expanding outward from the metropolitan areas in the mouth of the basin.
As expected, none of the watersheds in Minnesota are in perfect health. Due to comprehensive landscape changes and a growing human population, all five components of watershed health have been degraded to some degree, although the drivers of degradation differ by region.
- Intensively cultivated watersheds in the Minnesota River and Red River basins are responding to a range of low scores particularly for perennial cover, hydrologic storage, terrestrial habitat quality, terrestrial habitat connectivity, riparian connectivity and pollution from non-point sources.
- The northeastern portion of the state, which is primarily forested with lower population densities, has lower scores for point-source pollution from mines, extensive forest harvest and airborne sources of mercury. Additionally, steep slopes and erodible soils have lower scores as health risk factor that will respond to changes to land cover and increasingly intense rainfall and snowmelt events.
- The Twin Cities metropolitan area and the corridors of development that lead to St. Cloud and Rochester have lower health scores for impervious surfaces, intensity of water use and point source pollution. There are pockets of natural lands and healthy waters, but they are often isolated due to the intensity of land use that accompanies urban development leading to low connectivity health scores as well.
- The highest health scores were consistently found in extreme north central Minnesota, primarily within the Peatlands Ecological Classification. These watersheds have a high percentage of their landscape in wetland and forested cover with correspondingly low development or agricultural use.
Supporting science
Scientific literature support
The WHAF Framework approach to scoring watershed health has been thoroughly documented including comparisons to other approaches for scoring watershed health and the criteria used for selecting this approach (see Knudsen et al., 2024). The basic approach follows the methodology used by a class of ecological health or risk assessments that uses individual metrics grouped into specific attributes or components of ecological health that are then ultimately combined into a single overall composite measure (typically by taking an unweighted or weighted average) (Vollmer et al., 2016).
The method used for scoring follows a hierarchy where multiple indices are grouped into the five components of hydrology, biology, connectivity, geomorphology, and water quality (Annear et al., 2004) yielding individual component scores which are then combined into a final watershed score. This method of measuring watershed health allows natural resource managers to examine the overall condition of watersheds but also easily dive into the specific indices which are directly comparable across watersheds. This approach also enables users to be able to identify potential relationships between scores within and across components that emerge at various spatial scales and encourage further investigation.
Confidence in index
Many national and statewide/regional integrated assessments that take this form are endorsed by the United States Environmental Protection Agency (US EPA) Healthy Watersheds Program. (USEPA2024a) The WHAF is one of the statewide assessments endorsed by this program alongside other statewide, local, or national examples, each of which vary in specific goal, metrics, and form (see “Examples of Integrated Assessments for Watershed Health” (USEPA, 2024b)).
Future enhancements
As the WHAF health scores are refined and improved, the combined statewide score will be recalculated. Over time, the combined score will better reflect what is known about ecological system health in Minnesota. There are also new health scores that are added to the WHAF that will be incorporated into the combined score. Additionally, health score values that are re-calculated over time will create an opportunity to track changes in the health status of Minnesota’s watersheds. Future plans include the exploration of the influence of weighted scoring and expansion of change over time inputs.