The Changing Nature of Water Storage in the Great Lakes Basin and its Implications for Future Sustainability

Home to approximately 40 million people in the United States and Canada, the Great Lakes drainage basin is a tremendous freshwater resource. It is, however, undergoing significant changes both in land use and climate. It has suffered from substantial deforestation in the last century and the continued drainage of wetlands. Reforestation, urbanization and increased demand for agricultural production on less land are all changing the face of the region. Climate is also changing with warmer, wetter winters changing the accumulation of snow and the formation of lake and soil ice. When land use and climate are relatively consistent between years, the storage of water in and on the land surface can be neglected for inter-annual analysis of the regional water balance, however, given the observed and projected future changes to the region it is clear that representing changes in storage will be critical for understanding how hydrology in the region will respond. As nearly half of the freshwater supply to the Great Lakes is in the form of land surface runoff, changes in the volume and timing of water storage within the drainage basin is a critical factor in the future health and sustainability of their ecosystem. Unlike air temperature and precipitation which are fairly well known in the region, many of these storage variables are known at only a handful of locations if they are monitored at all. Therefore, hydrology model become indispensable tools when trying to quantify changes in storage. For this presentation, observed and simulated datasets are used to identify and quantify changes in the timing and quantity of storage within the Great Lakes region due to changes in land use and climate. Storage terms that will be evaluated include soil moisture and ice, snow cover, groundwater, and inland lake and wetland storage. Warmer winters are reducing snow cover, which can lead to the formation of more soil ice and wetter spring soils for a time, though increasing temperatures will get warm enough to reduce the formation of soil ice as well. Wetter and warmer conditions in the winter and spring can lead to earlier spring runoff, though the presence of lake and wetland storage can mitigate this effect. Wetlands and lakes increase infiltration and the potential for groundwater recharge, while the expansion of urban impervious area reduces infiltration and recharge.