Simulated impacts of relative climate change and river discharge regulation on sea ice and oceanographic conditions in the Hudson Bay Complex

Abstract

In this analysis, we examine relative contributions from climate change and river discharge regulation to changes in marine conditions in the Hudson Bay Complex using a subset of five atmospheric forcing scenarios from the Coupled Model Intercomparison Project Phase 5 (CMIP5), river discharge data from the Hydrological Predictions for the Environment (HYPE) model, both naturalized (without anthropogenic intervention) and regulated (anthropogenically controlled through diversions, dams, reservoirs), and output from the Nucleus for European Modeling of the Ocean Ice-Ocean model for the 1981–2070 time frame. Investigated in particular are spatiotemporal changes in sea surface temperature, sea ice concentration and thickness, and zonal and meridional sea ice drift in response to (i) climate change through comparison of historical (1981–2010) and future (2021–2050 and 2041–2070) simulations, (ii) regulation through comparison of historical (1981–2010) naturalized and regulated simulations, and (iii) climate change and regulation combined through comparison of future (2021–2050 and 2041–2070) naturalized and regulated simulations. Also investigated is use of the diagnostic known as e-folding time spatial distribution to monitor changes in persistence in these variables in response to changing climate and regulation impacts in the Hudson Bay Complex. Results from this analysis highlight bay-wide and regional reductions in sea ice concentration and thickness in southwest and northeast Hudson Bay in response to a changing climate, and east-west asymmetry in sea ice drift response in support of past studies. Regulation is also shown to amplify or suppress the climate change signal. Specifically, regulation amplifies sea surface temperatures from April to August, suppresses sea ice loss by approximately 30% in March, contributes to enhanced sea ice drift speed by approximately 30%, and reduces meridional circulation by approximately 20% in January due to enhanced zonal drift. Results further suggest that the offshore impacts of regulation are amplified in a changing climate.

Representing climate evolution in ensembles of GCM simulations for the Hudson Bay System

“…First, the number of 19 simulations was determined as the threshold to explain roughly 90% of the variance of the 54 simulation ensemble, following the cost-benefit optimization proposed by Casajus et al (2016, supporting information S2). To assess climate change impacts in BaySys, both on the hydrological systems around the Hudson Bay, as well as the water body of Hudson Bay itself, it was important to include CMIP5 climate simulations that provided the variables and temporal resolution required to drive the NEMO ocean model for the Hudson Bay marine domain (Lukovich et al, 2021). Overall, accessible data archives contained 5 simulations for which the required 3-hourly data for driving NEMO were available, providing temperature, precipitation, surface pressure, longwave and shortwave radiation, specific humidity and wind.…”

“…Minimum temperature, maximum temperature, and total precipitation at the daily resolution are the primary variables considered for climate scenario selection assessment of the climate ensembles in this study. Although additional variables were used to drive the ocean models, they were not considered as influential in driving change within the ocean system as temperature and precipitation (Lukovich et al, 2021).…”

“…To provide the hydrology and ocean circulation modeling groups within BaySys with transient climate information, two climate simulation ensembles were developed using a combination of meeting data availability constraints and the k-means clustering approach proposed by Casajus et al (2016). A larger ensemble of 19 simulations at daily temporal resolution was provided to the BaySys hydrological modeling team (MacDonald et al, 2018, and a smaller subset of 5 climate scenarios was used by the BaySys ocean modeling team needing subdaily resolution and additional variables like air pressure, wind, and solar radiation (Lukovich et al, 2021). To ensure adequate diversity in future climate scenarios was captured by the smaller subset, an in-depth assessment of climate scenario performance between the larger hydrologic climate ensemble and ocean subset was needed.…”

“…Within the BaySys research program, several recent studies examine the regional and HBDB-wide hydrologic changes associated with climate impacts based on the larger climate scenario ensemble (MacDonald et al, 2018;Lilhare et al, 2019;Stadnyk et al, 2019;, and one over the extended pan-Arctic domain using the smaller climate scenario subset ensemble , Lukovich et al, 2021. More studies are currently underway; therefore, it is important to understand the differences and similarities among the two ensembles, and their relative variability, given their influence on recent literature.…”

“…Using a set of climate indicators proposed by the Expert Team on Climate Change Detection and Indices (ETCCDI; http:// etccdi.pacificclimate.org/list_27_indices.shtml), we examine to what extent the smaller subset is representative of the larger ensemble in terms of the evolution of historical climate across the terrestrial domain, and the projected changes for two future periods (near future: 2021-2050, far future: 2041-2070). This article focuses on climatic change across the terrestrial domain, and Lukovich et al (2021) address changes over the marine system domain.…”