Improved representation of hydrological processes in CLASS

Here, I provide a short summary of a recent research that we undertook to improve the Canadian Land Surface Scheme (CLASS) in terms of hydrological processes. Regional and global climate model simulated streamflows for high-latitude regions show systematic biases, particularly in the timing and magnitude of spring peak flows. Though these biases could be related to the snow water equivalent and spring temperature biases in models, a good part of these biases is due to the unaccounted effects of non-uniform infiltration capacity of the frozen ground and other related processes. In this research, the treatment of frozen water in the Canadian Land Surface Scheme (CLASS), which is used in the Canadian regional and global climate models, is modified to include fractional permeable area, supercooled liquid water and a new formulation for hydraulic conductivity. The impacts of these modifications on the regional hydrology, particularly streamflow, were assessed by comparing the original and modified versions of CLASS over a northeast Canadian domain.

Results suggest statistically significant decreases in infiltration and therefore soil moisture during the snowmelt season for the simulation with the new hydraulic conductivity and matric potential formulations and fractional permeable area concept compared to the original version of CLASS, which is also reflected in the increased spring surface runoff (figure) and streamflows in this simulation with modified CLASS over most of the study domain. The simulated spring peaks and their timing in this simulation are also in better agreement to those observed.

Consult http://link.springer.com/article/10.1007/s00704-015-1618-4 for details

Figure: Mean daily surface runoff (mm/day) for the months of May, June, and July for the original version of CLASS (top row) and the differences in surface runoff between modified and original versions of CLASS. Values are shown only for grid cells where the differences are statistically significant at 95 % confidence level. The offline simulations were driven by ERA-Interim for the 1970-2001 period.

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