Assessing Climate Change under Future Warming Scenarios with Improved Canopy Snow Representation in CESM

Abstract:

Boreal forests are a major source of land surface shortwave radiation bias in current generation earth system models. We incorporate a modified canopy scheme into the Community Land Model with snow interception as a prognostic variable to alleviate the source of some biases. Maximum interception limits and snow unloading are adjusted to in-situ canopy measurements. The canopy radiation scheme has been updated from a direct temperature dependence of optical parameters to a dependence on the prognostic snow storage. With these improvements, boreal forest zones show large, significant albedo error reductions relative to MODIS observations. Model gridcell error reduction during spring results from a more gradual seasonal transition in albedo, while error reduction in winter is from a lower albedo. Error is also reduced overall for North Hemisphere land area.

We assess the impacts of the snow canopy vegetation treatment in coupled model warming scenarios. Little change in global albedo feedback or climate sensitivity were shown, but significant regional and temporal variations resulted, partly from changing circulation patterns