Abstract
Regional climate modelling represents an appealing approach to projecting Great Lakes water supplies under a changing climate. In this study, we investigate the response of the Great Lakes Basin to increasing greenhouse gas and aerosols emissions using an ensemble of sixteen climate change simulations generated by three different Regional Climate Models (RCMs): CRCM4, HadRM3 and WRFG. Annual and monthly means of simulated hydro-meteorological variables that affect Great Lakes levels are first compared to observation-based estimates. The climate change signal is then assessed by computing differences between simulated future (2041–2070) and present (1971–1999) climates. Finally, an analysis of the annual minima and maxima of the Net Basin Supply (NBS), derived from the simulated NBS components, is conducted using Generalized Extreme Value distribution. Results reveal notable model differences in simulated water budget components throughout the year, especially for the lake evaporation component. These differences are reflected in the resulting NBS. Although uncertainties in observation-based estimates are quite large, our analysis indicates that all three RCMs tend to underestimate NBS in late summer and fall, which is related to biases in simulated runoff, lake evaporation, and over-lake precipitation. The climate change signal derived from the total ensemble mean indicates no change in future mean annual NBS. However, our analysis suggests an amplification of the NBS annual cycle and an intensification of the annual NBS minima in future climate. This emphasizes the need for an adaptive management of water to minimize potential negative implications associated with more severe and frequent NBS minima.
Highlights
Over the last decades, there has been growing concern about the hydrological responses of the Great Lakes to global warming, stemming from potential changes in Great Lakes water level variability and the frequency of extremes under an evolving climate
These are derived from fitted Generalized Extreme Value (GEV) distributions to the extreme Net Basin Supply (NBS) values coming from the AMNO Canadian RCM Version 4 (CRCM4) simulations
Studies based on Bchange factor^ method applied to a suite of models generally lead to the conclusion that Great Lake water levels may significantly decline in future climate
Summary
There has been growing concern about the hydrological responses of the Great Lakes to global warming, stemming from potential changes in Great Lakes water level variability and the frequency of extremes under an evolving climate. The change factors in climate variables, typically derived from different Global Climate Model (GCM) projections, serve to perturb observed historical time series. Perturbed time series are used as input to the AHPS, which compute future time sequences of the Great Lakes Net Basin Supply (NBS). The NBS is the primary driver of the Great Lakes levels. These can be derived by applying the latest version of Great Lakes Channel Routing and Regulation model (Hartmann 1988) using the NBS time sequences as input. It is important to highlight that AHPS is primarily intended for seasonal forecasting, and not necessarily for longer-term climate-scale projections, in which energy and water budget conservation play an important role
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