Present and future Laurentian Great Lakes hydroclimatic conditions as simulated by regional climate models with an emphasis on Lake Michigan-Huron

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 hydrometeorological 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.

Assessment of the Laurentian Great Lakes’ hydrological conditions in a changing climate

“…A comparison between the 1962-1990 and 2021-2050 periods revealed NBS changes between −9 and +1% depending on the lake, and small water level decreases ranging from 3 to 6 cm (MacKay and Seglenieks 2013). Music et al (2015) obtained an ensemble median of 0 mm day −1 for NBS changes between 1971-1999 and 2041-2070 for lake Michigan-Huron.…”

“…In this context, anticipating how climate change may alter the water balance of the lakes in the decades to come is of the utmost importance (Gronewold et al 2013). In doing so, past studies have focused on estimating net basin supply (NBS) as a main driver of lake levels (Croley 1990;Hartmann 1990;Lofgren et al 2002;Deacu et al 2012;MacKay and Seglenieks 2013;Music et al 2015). NBS represents the simplified hydrological balance of a lake, expressed as a water depth, such that…”

“…As a result, a better representation of feedback processes and a finer hydrological sensitivity can be attained (Wood et al 2004;Leung et al 2004). As such, recent studies relying on RCMs and coupled lake models have reported much less dramatic declines in NBS (e.g., MacKay and Seglenieks 2013;Music et al 2015;Notaro et al 2015). A comparison between the 1962-1990 and 2021-2050 periods revealed NBS changes between −9 and +1% depending on the lake, and small water level decreases ranging from 3 to 6 cm (MacKay and Seglenieks 2013).…”

“…Using this project's newest generation of RCM makes this study relevant as it updates the results of older hydrological studies focusing on the Great Lakes region. Along with recent models, representative concentration pathways (RCPs) are used instead of previously applied scenarios from the Special Report on Emissions Scenarios (SRES; e.g., Angel and Kunkel 2010;Hayhoe et al 2010;Music et al 2015).…”

“…Doing this will increase our understanding of climate change impacts within a monthly time threshold that was used in previous analyses (e.g., Notaro et al 2015). This time scale is also more appropriate to the study of extreme events that were previously assessed using monthly time series (Music et al 2015).…”