Projected extreme temperature and precipitation of the Laurentian Great Lakes Basin

Abstract

Abstract The Laurentian Great Lakes Basin has been subject to increasingly extreme weather events in the past seven decades. This study uses a regional climate model spanning the region to project summer maximum temperature (Tmax), winter minimum temperature (Tmin), and seasonal extremes of precipitation for the mid-century (2030–2059) and late-century (2060–2089) relative to the baseline period (1980–2009). The basin's southern portion (US side) summer Tmax increases are projected to be greater than those in the northern portion of the basin (Canadian side), whereas Canadian side winter Tmin increases will be greater than those on the US side. The annual number of extremely hot days (Tmax ≥ 32 °C) in this region during mid-century and late century periods is projected to rise by 6.1–15.3 days and 10.0–32.1 days relative to the baseline period (1980–2009) values (0.1–21.5 days), respectively; whereas the annual number of extremely cold days (Tmin ≤ −18 °C) is projected to be reduced by 3.9–6.2 days (mid-century) and 5.5–9.9 days (late century) compared to the baseline period (2.6–60.5 days). The annual number of extremely cold days is projected to remain unchanged in 23%–61% of the area over the Lakes. The Basin's annual precipitation is projected to rise continuously but the degree of change will vary by season. Winter and spring precipitations are projected to rise greatly, autumn precipitation will rise to a lesser extent, but summer precipitation is projected to decline relative to the baseline period. The annual number of extremely wet days (≥40 mm/day) over the Lakes only is projected to increase by between 0.3 and 0.6 days (mid-century) and 0.5–0.8 days (late century). The annual number of extremely wet days over land areas is projected to increase by 0.2–0.6 days and 0.5–0.8 days, respectively. However, about 20% of the region will also experience a reduced number of extremely wet days, which implies that future precipitation changes in this region may be quite different at smaller scales (e.g. county to county) than over larger scales. We propose that lake and land differences, seasonal variations, and changed and unchanged areas should all be considered in climate studies of regions within which large inland water bodies reside, as these regions will have similarities with the Great Lakes basin.