Theme C : Land-surface processes enhanced by improved representation of surface heterogeneity

High-resolution RCMs represent formidable laboratories that can be put to use to further our understanding of the complex interactions and feedback that shape weather and climate of Canada’s Nordic and Arctic regions. We plan to undertake a series of experiments to quantify the role and importance of explicitly resolving processes taking place in the land and atmosphere components of the regional Earth System and the interactions between them as such interactions are paramount in determining our immediate living environment. The Canadian Nordic and Arctic regions with their innumerable lakes, wetlands, glaciers, rivers, snow-cover and permafrost, present distinct challenges to climate modelling. As grid meshes of models approach 10 km, regional water bodies and land-surface heterogeneities begin to be explicitly resolved, thus allowing realistic feedback processes that will increase the realism of climate simulations and improve climate-change projections. A recent study by Lawrence et al. (2008) showed that when Arctic sea ice is in rapid decline, the rate of predicted warming over surrounding land more than triples. This could result in important changes to the Canadian snow-cover and permafrost, which in turn can lead to changes in the regional hydrology.

Through methodically designed numerical experiments using the available modelling and observational tools, several important science questions relating to Canada’s climate will be addressed, such as: How do vegetation, lakes, snow-cover, permafrost and glaciers modulate Canada’s climate? What is the impact of retreating glaciers and reduced snow cover on regional hydrology? What formulation of the Great Lakes is required to adequately simulate the climate and hydrology of the region? Are current model formulations of snow-albedo feedback in agreement with observations? What resolution is required to adequately simulate lake-effect snow-belt, mountain snowpacks and glacier mass balance? How has terrestrial Arctic drainage changed in recent decades? What are the impacts of rapid ice-loss events on the hydrology and climate of the surrounding land region?

Research Projects

A new atmospheric boundary-layer (ABL) scheme based on an equilibrium turbulent kinetic energy (TKE) formulation has been developed and tested in the single column model (SCM) employing the CCCma 4th-generation atmospheric physics package which is the basis for CCCma's regional (CanRCM4) and global (CanAM4) climate models. This scheme has been coupled to a stochastic parameterization of the effects of intermittent mixing in the stable ABL.

To better resolve the changing snowmelt and glacier hydrology of western North America, improved representations of surface heterogeneity, snowpack processes and snow-albedo feedback are needed in the current generation of RCMs. Multiple factors control mountain snowpack accumulation and ablation, including elevation, slope, aspect, wind, and vegetation. Snow melt is also affected by the evolution of the snowpack through the melt season, e.g.

Glacier retreat is ubiquitous in the world’s mountain and polar-regions, reshaping the landscape, impacting regional hydrology (e.g., Huss, 2011), and contributing to global sea level rise (Radic and Hock, 2011). Areal changes in glacier extent can be measured by satellite and are well documented (e.g., Paul et al., 2004; Bolch et al., 2010), but mass balance and volume changes need to be measured in the field and modelled through glaciological and regional climate models (RCMs).

When vegetation is modelled as a dynamic component of the climate system, then the structural attributes of vegetation (leaf area index, vegetation height and rooting depth) are able to respond to changes in climate and this in turn also affects the climate. Studies have shown that these bi-directional interactions, between the vegetation and climate, increase the variability of climate (Crucifix et al., 2005; Wang et al., 2011). In this regard, vegetation influences the extremes of climate. The Canadian Terrestrial Ecosystem Model (CTEM) has recently been implemented in CRCM5.

Lakes are important components of the climate system and can affect regional climate by modulating surface albedo, surface energy and moisture budgets. The earlier versions of CRCM did not have lakes, except for the Great Lakes that were modelled using a mixed-layer lake model with thermodynamic ice treatment. Based on the offline analysis of available lake models (Martynov, 2010), it was decided to retain two lake models, the Hostetler model (Hostetler, 1993) and the Flake model (Mirinov, 2007), which were implemented in CRCM5.

One of the most important features of the Canadian high-latitudes is permafrost. Till recently, climate models, both global and regional, were not capable of simulating near-surface permafrost. This was mostly due to the limitation that GCMs and RCMs employ land-surface schemes that vary in depth between 3 and 10 meters.

The increased recognition of the importance of land-climate interactions and feedbacks in modulating regional climate highlights the need for realistic representation of land-surface types and processes in climate models. The current versions of Canadian RCMs use adavanced state-of-the-art land-surface scheme CLASS. It was shown in some recent studies (e.g. Koster et al., 2004; Seneviratne et al., 2006) that in some areas and under some conditions, the state of the land surface systematically affects the atmospheric variability, particularly temperature and rainfall. Koster et al.