The intraannual variability of land‐atmosphere coupling over North America in the Canadian Regional Climate Model (CRCM5)

• Published in: Journal of geophysical research. Atmospheres 2016-12, Vol.121 (23), p.13,859-13,885
• Main Authors: Yang Kam Wing, G., Sushama, L., Diro, G. T.
• Format: Article
• Language: English
• Subjects: Air temperature; Albedo; Amplification; Atmosphere; climate change; Climate models; Cloud cover; Computer simulation; Coupling; Freezing; Geophysics; Herbivores; land‐atmosphere coupling; Moisture content; North America; Phase transformations; Prairies; regional climate model; Snow; Snow depth; Soil moisture; Soil water; Spring; Summer; Surface temperature; temperature extremes; Water depth
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1002/2016JD025423

This study investigates the intraannual variability of soil moisture‐temperature coupling over North America. To this effect, coupled and uncoupled simulations are performed with the fifth‐generation Canadian Regional Climate Model (CRCM5), driven by ERA‐Interim. In coupled simulations, land and atmosphere interact freely; in uncoupled simulations, the interannual variability of soil moisture is suppressed by prescribing climatological values for soil liquid and frozen water contents. The study also explores projected changes to coupling by comparing coupled and uncoupled CRCM5 simulations for current (1981–2010) and future (2071–2100) periods, driven by the Canadian Earth System Model. Coupling differs for the northern and southern parts of North America. Over the southern half, it is persistent throughout the year while for the northern half, strongly coupled regions generally follow the freezing line during the cold months. Detailed analysis of the southern Canadian Prairies reveals seasonal differences in the underlying coupling mechanism. During spring and fall, as opposed to summer, the interactive soil moisture phase impacts the snow depth and surface albedo, which further impacts the surface energy budget and thus the surface air temperature; the air temperature then influences the snow depth in a feedback loop. Projected changes to coupling are also season specific: relatively drier soil conditions strengthen coupling during summer, while changes in soil moisture phase, snow depth, and cloud cover impact coupling during colder months. Furthermore, results demonstrate that soil moisture variability amplifies the frequency of temperature extremes over regions of strong coupling in current and future climates. Key Points Soil water phase determines soil moisture‐temperature coupling during spring and fall over the Canadian Prairies Soil moisture variability amplifies the frequency of temperature extremes in both current and future climates Projected changes to coupling during cold months are due to changes in soil water phase, snow depth, and cloud cover