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The role of soil moisture-atmosphere interactions on future hot-spells over North America as simulated by the Canadian Regional Climate Model (CRCM5)

This blog is about our recent modeling study within CNRCWP aimed at exploring the role of future soil moisture-atmosphere interactions on projected hot-spell characteristics using the fifth generation Canadian Regional Climate Model (CRCM5). With this objective, two sets of CRCM5 simulations, driven by two coupled general circulation models (MPIESM and CanESM2), are performed with and without soil moisture-atmosphere interactions for current (1981-2010) and future (2071-2100) climates over North America, for Representative Concentration Pathways (RCPs) 4.5 and 8.5. Analysis indicates that, in future climate, the summer soil moisture-temperature coupling regions, located over the Great Plains in current climate, will expand further north, including large parts of central Canada.

One of the interesting results we found is that the contribution of future changes in soil moisture-atmosphere interactions to the projected increase in hot-spell days is higher for the RCP4.5 than for RCP8.5 Scenario (although it is well known that the projected increases in future hot-spell days are usually higher for RCP8.5 than for RCP4.5 scenario). For instance, according to the analysis, over Central Canada, more than 50% of the projected increase in hot-spell days (Fig 1) is due to changes in land-atmosphere interactions. This higher contribution of soil moisture-atmosphere interactions for RCP4.5 scenario to the future increases in hot spell days, despite decreases in soil moisture, is because the future soil moisture values are representative of transitional regime between wet and dry state which are conducive to soil moisture-atmosphere coupling. For RCP8.5 scenario, on the other hand, future drying reduces soil moisture to that typical of very dry conditions, which reduce evapotranspiration significantly, and thus the impact on temperature or hot-spell days.

Figure: The top panels show projected changes to hot-spell days (HSD, in days) in CRCM5 simulations driven by MPI-ESM and CanESM2 GCMs, for RCP4.5 and RCP8.5 scenarios. The contribution (in %) of soil moisture-atmosphere coupling changes to HSD changes are shown in the bottom panels.

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