Atmospheric water budget over the Great Lakes Region and the effects of climate change

Precipitation provides an important source of water for human and agricultural use, therefore understanding how precipitation will change under future climate has important societal implications. The Great Lakes, an important source of surface fresh water for North America, are located in the midlatitude transition zone with some climate models predicting an increase in precipitation under warmer climates and others predicting a decrease in precipitation. In order to understand precipitation changes in the region, we evaluate components of the atmospheric water budget over the Great Lakes with four reanalysis products (NASA MERRA, NCEP CSFR, NARR, and ERA-Interim) to better understand how the region's moisture is simulated by current models. The water budget is calculated as the moisture flux into a region plus the local evapotranspiration minus water lost as precipitation. Most of the reanalysis products simulate more precipitation than observed in the Great Lakes region. Transport of moisture is the dominant source of moisture in the region, with the strongest inflow at the western boundary of the Great Lakes region. Evapotranspiration estimates vary widely between all four reanalysis products. We discuss the implications of these results for present-day and future climate model simulations and highlight key features that atmospheric models should capture for accurate simulation of precipitation in the Great Lakes region.