Water for Forest Lands for the Upper Mississippi River

Forests provide the most stable and highest quality water supplies among all land uses. Forests cover around 34.6 percent of the land in Minnesota and 49.1 percent in Wisconsin. All of the forests in Minnesota and Wisconsin are owned and managed by either federal, state, local (county and local governments), or private entities, thus it is critical to understand the role of these forest lands in providing water across the state and region.

The relative contribution of forests to the total water supply can be estimated for any point along a stream network-such as the location of a drinking water intakes-by tracking water yield from forested lands through the river network. We used computer modeling and spatial analyses to quantify surface water supply originating on public (federal, state, and local) and private (corporate, other private, and tribal) forest lands for Minnesota and Wisconsin at the 12-digit Hydrologic Unit Code watershed scale between 2000 and 2010, using the Water Supply Stress Index (WaSSI) hydrologic model. Water originating on seven forest ownership types was tracked through the river network and linked to a database of surface drinking water intakes to quantify the population served by water from SPF lands across the two states. We found that the area of SPF lands was 28.0 percent of the total land area in Minnesota and Wisconsin. Federal, state, local, private (FSLP) forest lands accounted for 39.2 percent of the total land area in Minnesota and Wisconsin. SPF lands contributed 21.9 percent of the 8.7 million cubic meter per year total available surface water supply in Minnesota and Wisconsin. While FSLP forest lands accounted for 27.6 percent of the 8.7 million cubic meter per year total available surface water supply in Minnesota and Wisconsin. We used computer modeling and spatial analyses to quantify surface water supplied at water shed outlet across Minnesota and Wisconsin using the Water Supply Stress Index Model (WaSSI).

WaSSI is an integrated monthly water balance and flow routing model that simulates the full hydrologic cycle for each of 10 land-cover classes in the 2099 Watershed Boundary Dataset (USGS, 2010) to asses the impact of climate change, land use change, and population growth on water supply stress, river flows, and ecosystem productivity across the conterminous United States (Caldwell et al., 2011; Caldwell et al., 2012; Sun et al. 2011). The WaSSI model has been successfully used in climate change assessments in the Eastern United States (Lockaby et al., 2011; Marion et al., 2012) and examining the nexus of water and energy at the national scale (Avery et al., 2011) and is the best available tool to quantify surface water supplied by National Forests to communities across broad regions. The data inputs for the WaSSI Model is shown below in Table 1.

The WaSSI water balance module computes the water balance independently for each of several land cover classes in each watershed or grid cell (see Figure 1).

For more information on the WaSSI Ecosystem Services Model, visit the  WaSSI User Guide .

Drinking water is one of our most valuable resources because we need it to survive, but where does it come from?

For more information on forest ownership, visit  Forest Ownership in the Conterminous United States .

Mean annual  water yield  ranged from 278.2 mm/yr (10.9 inches per year) in Minnesota and Wisconsin.  Water supply  originating on SP forest lands in Minnesota and Wisconsin contributed 21.9 percent of the 8.7 million cubic meter per year and FSLP forest lands contributed 27.6 percent.

Approximately 500,000 people in Minnesota and Wisconsin derived some portion of their drinking water (>0 percent of the total supply) from SPF lands. This represents - percent of the total population in the region. In addition, approximately 10.3 million people outside Minnesota and Wisconsin recieved some portion of their drinking water from the SPF lands in Minnesota and Wisconsin. State and private forest in the MN and WI provide more than 30 percent of water supply for 270,000 people within the two states.

 Ning Liu , Postdoctoral Research Fellow, U.S. Department of Agriculture Forest Service, Southern Research Station, Coweeta Hydrologic Lab, and University of Minnesota, College of Natural Resources, Department of Forest Resources, 301H Green Hall, St. Paul, MN 5510.

 G. Rebecca Dobbs , Geospatial Research Associate, U.S. Department of Agriculture Forest Service, Southern Research Station, Coweeta Hydrologic Lab, Otto, NC 28763, and North Carolina State University, College of Natural Resources, Department of Forestry and Environmental Resources, Center for Geospatial Analytics, Raleigh, NC 2769.

 Peter V. Caldwell , Research Hydrologist, U.S. Department of Agriculture Forest Service, Southern Research Station, Coweeta Hydrologic Lab, Otto, NC 2876.

 Chelcy Ford Miniat , Research Ecologist, U.S. Department of Agriculture Forest Service, Southern Research Station, Coweeta Hydrologic Lab, Otto, NC 2876.

 Paul V. Bolstad , Professor, University of Minnesota, College of Natural Resources, Department of Forest Resources, St. Paul, MN 5510.

 Stacy Nelson , Professor, North Carolina State University, College of Natural Resources, Department of Forestry and Environmental Resources, Center for Geospatial Analytics, Raleigh, NC 2769.

 Ge Sun , Research Hydrologist, U.S. Department of Agriculture Forest Service, Southern Research Station, Eastern Forest Environmental Threat Assessment Center, Forestry Sciences Laboratory, Research Triangle Park, NC 27709. 

 Mattie Gisselbeck , Research Assistant, University of Minnesota, College of Natural Resources, Department of Forest Resources, St. Paul, MN 5510.

Homer, C., Dewitz, J., Jin, S., Xian, G., Costello, C., Danielson, P., Gass, L., Funk, M., Wickham, J., Stehman, S., Auch, R., & Riitters, K. (2020). Conterminous United States Land Cover Change Patterns 2001–2016 from the 2016 National Land Cover Database. ISPRS Journal of Photogrammetry and Remote Sensing, 162, 184–199.  https://doi.org/10.1016/j.isprsjprs.2020.02.019 

Marion, D., Sun, G., Caldwell, P., Miniat, C., Ouyang, Y., Amatya, D., Clinton, B., Conrads, P., Laird, S., Dai, Z., Clingenpeel, J., Liu, Y., Roehl, E., Meyers, J., & Trettin, C. (2013). Managing Forest Water Quantity and Quality under Climate Change. In J. Vose & K. Klepzig, Climate Change Adaptation and Mitigation Management Options (pp. 249–306). CRC Press.  https://doi.org/10.1201/b15613-10 

Sass, E. M., Butler, B. J., & Markowski-Lindsay, M. A. (2020). Forest Ownership in the conterminous United States circa 2017: Distribution of Eight Ownership Types - Geospatial Dataset. Forest Service Research Data Archive.  https://doi.org/10.2737/RDS-2020-0044 

USDA Forest Service. (2021). Family Forest (10+ acres) Ownership Characteristics: Wisconsin, 2018 (NRS-RN-308; p. NRS-RN-308). U.S. Department of Agriculture, Forest Service, Northern Research Station.  https://doi.org/10.2737/NRS-RN-308 

USDA Forest Service. (2021). Family Forest (10+ acres) Ownership Characteristics: Minnesota, 2018 (NRS-RN-282; p. NRS-RN-282). U.S. Department of Agriculture, Forest Service, Northern Research Station.  https://doi.org/10.2737/NRS-RN-282