COMBINED - Mean Watershed Score
The Mean Watershed Score combines the mean (average) score for each of the five components into an overall average watershed health score. Each of the five components has an equal influence on the combined Mean Watershed Score.
The Mean Watershed Scores decline from north to south, and east to west; with the lowest mean scores in the Red River and Minnesota River basins. These overall scores closely follow land uses that remove permanent vegetation, alter streams or increase impervious surface. Although combining all the scores will mask extreme values from any individual index, the overall Mean Watershed Score is a useful indicator to broadly compare watershed health across the state.
Mean Watershed Health Score
Creating the Index
- Data Inputs
The Mean Watershed Score is a 'mean of means' created by combining the 5 Component Mean Scores.
- Mean component health rankings
Each Mean Component health score has equal influence on the Combined Mean score.
Mean Water Quality
- Pattern of results
Although the Mean Watershed 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.
Click map to enlarge and explore Watershed Health Assessments:
- Interpreting results
As expected, none of the watersheds in Minnesota are in perfect health. Due to comprehensive landscape changes and a growing human population, all of the 5 components of watershed health have been degraded to some degree, although the drivers of degradation differ by region.
- These results indicate that intensively cultivated watersheds are the most degraded due to the loss of perennial cover, hydrologic storage, terrestrial habitat quality, terrestrial habitat connectivity, and riparian connectivity as well as pollution from non-point sources.
- The northeastern portion of the state, which is primarily forested with lower population densities, has been degraded by point-source pollution from mines, extensive forest harvest and airborne sources of mercury. It is also vulnerable to climate change and hyrologic alterations.
- The Twin Cities metropolitan area and developed corridors toward St. Cloud and Rochester are degraded due to impervious surfaces, intensity of water use and point source pollution. They also have limited connectivity due to the intensity of land use that accompanies urban development.
- 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.
Location matters. The healthier watersheds in Minnesota tend to be those furthest upstream. This trend can be seen in the Red, Rainy, Upper Mississippi and St. Croix Basins. Health problems travel through the system, and their cumulative effect reduces the health of the system downstream. Headwater watersheds that "export" water and are not recipients of sediment and contaminants, tend to have higher health scores then their downstream neighbors.
Headwater areas generally include steeper, more complex terrain so are historically less developed. Settlement occurred first in river confluence areas where commerce was occurring and flatter areas lent themselves to agricultural and human development. Over time, urban areas grow outward from their first historic population centers, often following river valleys and level landscape features.
- 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 and those are incorporated into the combined score.