Improving historical precipitation estimates over the Lake Superior basin

Abstract

[1] Lake Superior, the northern-most of the Laurentian Great Lakes, is the largest (by surface area) freshwater lake on the planet. Due in part to its high water surface to land area ratio, over one-third of the Lake Superior basin water budget is derived from precipitation falling directly on the lake surface. For most of the Great Lakes (including Lake Superior), historical precipitation estimates extend back to the early 1880s, and are based primarily on land-based gauge measurements. While alternatives to gauge-based estimates have been explored, there is no clear history of applying regional climate models (RCMs) to improve historical over-lake precipitation estimates. To address this gap in regional research, and to advance the state-of-the-art in Great Lakes regional hydrological modeling, we compare 21 years of output from an RCM to conventional gauge-based precipitation estimates for the same time period over the Lake Superior basin. We find that the RCM, unlike the gauge-based method, simulates realistic variations in over-lake atmospheric stability, which propagate into basin-wide precipitation estimates with a relatively low over-lake to over-land precipitation ratio in warm months (roughly 0.7 to 0.8 in June, July, and August) and a relatively high over-lake to overland precipitation ratio in cold months (roughly 1.3 to 1.4 in December and January), compared to gauge-based estimates. Our findings underscore a need to potentially update historical gauge-based precipitation estimates for large lake systems, including Lake Superior, and that RCMs appear to provide a robust and defensible basis for making those updates. Citation:

The role of meteorological processes in the description of uncertainty for climate change decision-making

“…The lakes' relatively cool surface waters during the warm season suppress convective clouds and reduce rainfall directly over them (Changnon and Jones 1972;Scott and Huff 1996). Observations of over-lake precipitation have historically been derived from land-based gauge measurements (an exception is the Blust and DeCooke (1960) study), so modeling studies have been used to simulate over-lake precipitation (Holman et al 2012). The simulations and observations agree that the ratio of over-lake precipitation to over-land precipitation is relatively low (high) during the warm season (cool season), but a regional model suggests more extreme ratios (Holman et al 2012).…”

“…Observations of over-lake precipitation have historically been derived from land-based gauge measurements (an exception is the Blust and DeCooke (1960) study), so modeling studies have been used to simulate over-lake precipitation (Holman et al 2012). The simulations and observations agree that the ratio of over-lake precipitation to over-land precipitation is relatively low (high) during the warm season (cool season), but a regional model suggests more extreme ratios (Holman et al 2012). Warm-season temperature gradients between air masses over the lake and land cause lake breezes that are known to generate shoreline low-level convergence, which increases thunderstorm activity over the land adjacent to the lakes (Changnon and Jones 1972).…”

Engaging Marina and Harbor Operators in Climate Adaptation

“…Marinas and harbors experience a variety of climate change impacts including shorter winters (Kling and Wuebbles 2005), warmer temperatures (U.S. Global Change Research Program 2009), more intense storms (Mortsch, Alden, and Scheraga 2003), reduction in ice cover (Wang et al 2012), and fluctuating lake levels (Holman et al 2012). Concurrently, marina infrastructure is aging and deteriorating, even as securing funding for needed improvements becomes increasingly difficult (USACE 2012).…”

“…Our climate is changing -often in unpredictable ways -and it is difficult to convey the inherent uncertainties of climate science predictions. For example, extraordinarily low lake levels in 2013 attracted much public attention and sparked many demands for action, even though existing science predicts a wide range of lake-level changes (Lofgren, Hunter, and Wilbarger 2011;Holman et al 2012), and lake levels rebounded in 2014. To curtail the potential roadblocks of climate change bias or mistrust of science, we provided current climate findings, related those predictions to risks faced by marina operators, explained the uncertainty of climate predictions, and focused our message on building resilience to a range of conditions.…”

Meeting Summaries

“…This need is particularly pronounced for model-derived estimates of basin-scale components of the Great Lakes water budget, many of which are either not observable or not monitored directly, or (in the case of overland precipitation and basin-scale runoff, among others) are observed with significant intrinsic and extrinsic bias and variability (Bolsenga 1979;Holman et al 2012).…”