Comparisons between CMIP5 and CMIP6 climate projections: Implications for assessing agriculture productivity, infrastructure resilience, and environmental health in Canada

Abstract:

Changes in climate can affect socioeconomic activities and environmental conditions in Canada. The Global Circulation Models (GCM) are commonly used to understand the climate conditions in the future. While the GCM outputs of Coupled Model Intercomparison Project (CMIP) Phase 5 have been used for impact assessment over the past few years, the simulation outputs of CMIP Phase 6 (CMIP6) models have been recently released. In this study, we first aim to compare the ensemble mean of CMIP5 and CMIP6 models with each other as well as with the NOAA and NCEP reanalysis over Canada. This is to have a general understanding of the expected difference between CMIPs and their performance during the historical period. Furthermore, we investigate the added value of multi-realizations ensemble per individual models of CMIP6 and CMIP5 over the eleven Canadian climatic zones. For this purpose, we focus on a set of climatic indices that are important for human and ecosystem health, agricultural activities, and infrastructure resilience, which will be affected by changes in climate conditions. These indices are namely, the number of extremely hot days, number of hot and dry days, growing degree days, mean precipitation during growing season, extreme precipitation, and number of freeze and thaw cycles. Overall, the expected difference between multi-model ensemble mean of CMIP5 and CMIP6 for the 6 indices is relatively small over Canada. Moreover, despite showing similar patterns of variations spatially, neither CMIP5 nor CMIP6 ensemble means perfectly match the reanalysis data, in particular for growing degree days. In addition, considering the climatic zones, we note that the range of realizations for CMIP6 models do not necessarily cover corresponding CMIP5 realizations. In fact, the differences between the range and mean of realizations for individual models of CMIP5 and CMIP6 depend on the considered climatic index and vary moving from one climatic zone to another.