Wetlands are low-lands covered with water for a significant amount of the year. They are an important part of watershed hydrology as they provide temporary storage of surface water reducing flood potential downstream, increasing ground water recharge and reducing sediment and nutrient loads. Wetland dynamics are significantly affected by cold season processes, snow packs provide a large input of surface water in spring and soil frost reduces infiltration. Future climate projections for the Great Lakes region indicate that while annual average precipitation will not change much it will shift seasonally with more falling in the winter and spring and less in the summer. Annual average temperatures are expected to increase by 3 to 7°C in the winter reducing the duration and intensity of winter processes in the region. How these changes will affect the functionality of regional wetlands is an important question for assessing the future potential for floods, droughts and the extent to which wetlands continue to play a role in the hydrologic cycle.

This study focuses on the impact of retrospective and projected climate change on wetlands, and their hydrologic functionality. Wetlands and small lakes are represented in the Variable Infiltration Capacity (VIC) model for the state of Michigan. Lakes are parameterized using a database of lake area-depth relations for the state. Wetlands are parameterized by calibrating streamflow in watersheds with high wetland fractions over the last ten years to minimize the effects of continued wetland drainage. Retrospective climate simulations are performed for the period 1915-2006 using observed meteorological data. Future climate projections from 1950-2099 are downscaled and bias corrected based on general circulation models (GCMs) selected from the Intergovernmental Panel on Climate Change (IPCC) 4th assessment dataset. Selected lake and wetland, and hydrologic variables such as lake/wetland depth, lake ice temperature, lake ice height, soil moisture and temperature, and evapotranspiration as well as variables directly related to cold season processes such as soil ice content are analyzed with respect to 25-year periods of historic and future projected climate forcings. Changes in lakes and wetlands extent, their role in streamflow generation and how changes in cold season processes affect wetland variables are discussed.