Great Lakes net basin supply and lake levels under a changed climate based on a regional climate model

The Coupled Hydrosphere-Atmosphere Research Model (CHARM) was run for climate change scenarios over the Laurentian Great Lakes basin, with a particular view toward effects on the hydrology of the basin. This model incorporates the atmospheric and land surface portions of the Regional Atmospheric Modeling System (RAMS) version 6.0, along with a simple representation of the lakes in terms of vertical diffusion of heat and ice formation and melt. The results show a shift in peak river discharge from spring toward winter, due to reduced build-up and retention of snowpack. The model also shows some overall increase in both precipitation and evapotranspiration, from both the land and lake portions of the basin. The increase in precipitation, however, overbalances the increase in evapotranspiration on an annual mean basis, increasing the net basin supply and raising lake levels. This overall effect is in contrast to widely-cited results for this region that have been based on the use of hydrologic models coupled in a one-way fashion to general circulation models.