The Effect of Soil on the Summertime Surface Energy Budget of a Humid Subarctic Tundra in Northern Quebec, Canada.

Rising temperatures in the southern Arctic region are leading to shrub expansion and permafrost degradation. The objective of this study is to analyze the surface energy budget (SEB) of a subarctic shrub tundra site that is subject to these changes, on the east coast of Hudson Bay in eastern Canada. We focus on the turbulent heat fluxes, as they have been poorly quantified in this region. This study is based on data collected by a flux tower using the eddy covariance approach and focused on snow-free periods. Furthermore, we compare our results with those from six Fluxnet sites in the Arctic region and analyze the performance of two land surface models, SVS and ISBA, in simulating soil moisture and turbulent heat fluxes. We found that 23% of the net radiation was converted into latent heat flux at our site, 35% was used for sensible heat flux, and about 15% for ground heat flux. These results were surprising considering our site was by far the wettest site among those studied, and most of the net radiation at the other Arctic sites was consumed by the latent heat flux. We attribute this behavior to the high hydraulic conductivity of the soil (littoral and intertidal sediments), typical of what is found in the coastal regions of the eastern Canadian Arctic. Land surface models overestimated the surface water content of those soils but were able to accurately simulate the turbulent heat flux, particularly the sensible heat flux and, to a lesser extent, the latent heat flux. Significance Statement: Isostatic uplift after the last deglaciation led to the emergence of beaches, which represent a large area in the Canadian Arctic. We studied the surface energy budget of such a beach that emerged 6000 years ago in northeastern Canada. Results suggest that evaporation is up to 20% less than at previously studied sites, which is explained by sandy soils retaining little moisture despite abundant precipitation. Deployed numerical models showed difficulties in simulating the soil conditions but proved successful in simulating the surface energy budget after manual adjustments of the soil conditions. These simulation difficulties probably apply to other parts of the Canadian Arctic, possibly leading to errors in meteorological and climate forecasting. [ABSTRACT FROM AUTHOR]