State Water Resources Research Institute Program

Project Id: 2010MN270B
Title: Quantifying differential streamflow response of Minnesota ecoregions to climate change and implications for management
Project Type: Research
Start Date: 3/01/2010
End Date: 2/01/2011
Congressional District: 4
Focus Categories: Hydrology, Climatological Processes, Agriculture
Keywords: Watershed response, climate change, precipitation, evapotranspiration, agricultural drainage
Principal Investigators: Lenhart, Christian F; Nieber, John
Federal Funds: $ 0
Non-Federal Matching Funds: $ 45,287
Abstract: Climate change in the form of increased precipitation over the last few decades has contributed to increased streamflow in Minnesota, yet the relative importance of land-use, agricultural drainage and climate contributions are much disputed. However, it is clear that the rate of increased streamflow is not directly proportional to increased rainfall. Watersheds in different ecoregions respond differently to increased precipitation because variable climate, land-use, geology and hydrology in different ecoregions creates differential streamflow change. For example, in related research we have found that southern and western Minnesota watersheds have exhibited a much greater response to increased precipitation levels over the past 30 years than northern forested regions. The increased flows are greatest in the low to moderately high flow range with less significant increases in peak flow.

Increased streamflow creates numerous problems for water resources management such as increased sediment and nutrient loading rates and greater channel erosion. Changes to stream flow also impact aquatic habitat by changing the in-stream habitat conditions needed for animals such as riverine turtles and changing the conditions needed for aquatic vegetation establishment and growth. It is essential to understand the causes of recent changes in streamflow and potential increases in the near future to develop appropriate management activities for water supply, water quality and maintenance of ecological integrity. In order to do that it is necessary to determine the relative contributions of land-use, climate and drainage changes to increased streamflow.

The proposed project will document watershed response to climate change (in the form of precipitation change) by Minnesota ecoregion. Major objectives are to determine the contribution of increased rainfall to higher streamflow levels versus land-use and agricultural drainage changes. Changes in the runoff-generation process will characterized by the streamflow to precipitation (S:P) ratio. Through this research a better understanding of the hydrologic processes responsible for streamflow increases will be gained. Finally the project will aid in the prediction of potential future streamflow changes based on the range of watershed responses observed in the historical streamflow analysis.

Changes to streamflow in different Minnesota ecoregions will be assessed using the Indicators of Hydrologic Alteration (IHA) statistical program to compare pre-1980 streamflow characteristics with post-1980 streamflow and other relevant time periods. IHA measures streamflow change using 66 different parameters to characterize changes in the magnitude, duration, frequency and timing of low, medium and high flows.

Using a water budget approach, the S:P ratio can be calculated for different ecoregions of Minnesota. This data may then be used to separate out rainfall contributions to increased streamflow versus land-use and drainage-induced contributions. Using this S:P ratio (based on at least 60 years of data) the expected volume of streamflow from precipitation increases can be predicted. For example, if an ecoregion has an average S:P ratio of 1/5, then a precipitation increase of 3 inches over time would suggest a corresponding streamflow.

While the IHA data analysis will assist in identifying potential hydrologic mechanisms responsible for increased streamflow in Minnesota, modeling will be needed to further separate out land-cover (vegetative) and subsurface drainage contributions to increased streamflow. To determine the impact of land-cover (vegetation) changes on streamflow yield, different vegetation scenarios will be modeled at two research sites, using the Soil Water Atmosphere Plant (SWAP) model . The sites will include one northern forested watershed on the North Shore of Lake Superior and one subsurface pipe drained agricultural watershed, the Waseca Experimental station, in the Blue Earth watershed of south central Minnesota.

Using SWAP, soil-vegetation-climate interactions will be modeled for one Lake Superior north shore stream in the northern forested part of Minnesota and for the University Of Minnesota, Waseca Experimental station, representing a southern agricultural watershed with subsurface drainage. The northern Minnesota stream work will be done in conjunction with the North Shore Streams Sedimentation Project currently being conducted by Nieber et al. The Waseca site will be used to model differences in evapotranspiration rates for soybean and corn vs. grasslands and perennial plant crops; the major form of land-cover change in southern Minnesota in the last fifty years (Figure 2). In the northern watershed, differences in forest cover type will be modeled in addition to snowmelt changes driven by climate change (manifested as warmer winter temperatures).

The SWAP model will also be used to better understand water budget differences at the field scale, to determine the influence of subsurface tile pipe drainage on soil moisture and subsequent on streamflow. Several watershed scales will be examined since subsurface drainage is thought to reduce surface runoff at the field to small watershed scale but may increase low to mean flows at larger watershed scales as the cumulative volume of water is transported from the soil to streams.

The spatial distribution of watershed response will be mapped out using GIS. In order to spatially demonstrate the differences in streamflow response by Minnesota ecoregion, a map will be created that may be utilized for management and planning purposes.

Progress/Completion Report, 2010, PDF

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