PNNL

Abstract

The largest freshwater system on earth is experiencing all-time high water-levels in recent years. In this study, we used an extended version of the Dynamic Recycling Model to identify moisture sources and quantified their contributions to the long-term trends of the Great Lakes Region (GLR) precipitation. Results show that the mid-Pacific is the main moisture source to the GLR precipitation except in the summertime when terrestrial sources dominate. We explained the double peaks in seasonal precipitation cycle by dissecting its moisture sources. Moisture from the Great Plains is responsible for the June peak, and from the mid-Pacific, the Great Plains and the Central America for the September peak. We found a statistically significant increasing trend of GLR’s precipitation over the past 40 years, particularly in the cold-season. This increase is caused by an intensified zonal moisture transport from the mid-Pacific through changes in atmospheric circulation.