On the simulation of Laurentian Great Lakes water levels under projections of global climate change
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On the simulation of Laurentian Great Lakes water levels under projections of global climate change Murray MacKay & Frank Seglenieks
Received: 4 August 2011 / Accepted: 28 July 2012 / Published online: 16 August 2012 # Crown Copyright (Canada) 2012
Abstract A new method is proposed to estimate future net basin supplies and lake levels for the Laurentian Great Lakes based on GCM projections of global climate change. The method first dynamically downscales the GCM simulation with a regional climate model, and then bias—corrects the simulated net basin supply in order to be used directly in a river—routing/lake level scheme. This technique addresses two weaknesses in the traditional approach, whereby observed sequences of climate variables are perturbed with fixed ratios or differences derived directly from GCMs in order to run evaporation and runoff models. Specifically, (1) land surface—atmosphere feedback processes are represented, and (2) changes in variability can be analyzed with the new approach. The method is demonstrated with a single, high resolution simulation, where small changes in future mean lake levels for all the upper Great Lakes are found, and an increase in seasonal range—especially for Lake Superior—is indicated. Analysis of a small ensemble of eight lower resolution regional climate model simulations supports these findings. In addition, a direct comparison with the traditional approach based on the same GCM projections used as the driving simulations in this ensemble shows that the new method indicates smaller declines in level for all the upper Great Lakes than has been reported previously based on the traditional method, though median differences are only a few centimetres in each case.
1 Introduction The Laurentian Great Lakes basin is home for some 40 million inhabitants and hundreds of billions of dollars worth of commercial activity annually, as well as extensive and varied natural ecosystems. Understanding water level and flow regimes is thus of great interest. Lake levels, which have been monitored for more than 100 years, show a large degree of variability due to natural climate variability as well as direct human intervention (such as dredging, diversions etc.), and levels tend to oscillate between relatively high water periods M. MacKay (*) : F. Seglenieks Environment Canada, Climate Research Division, 4905 Dufferin Str., Toronto M3H-5T4, Canada e-mail: [email protected]
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Climatic Change (2013) 117:55–67
and relatively low water periods. The attribution of lake level fluctuations to specific causes is not straightforward, though recent record low levels in Lakes Superior and MichiganHuron have prompted some public outcry for immediate remedial action (e.g. see International Upper Great Lakes Study 2009). The possibility of bulk exports of Great Lakes water to outside the basin is a contentious political issue that is also raised from time to time. The situation is further complicated by the possibility of ongoing climate change, which could drive lake levels into regimes n
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