Implementation of lakes in the Canadian Regional Climate Model (CRCM): towards CRCM 5 Andrey Martynov, Rene Laprise, Laxmi Sushama University of Quebec in Ouranos Canadian regional climate modelling and diagnostics (CRCMD) Network

Canadian Regional Climate Model (CRCM) Regional climate modelling in Canada: mostly southern Canada, few attention paid to arctic regions. A new version of the Canadian RCM is being developed, better suited for Arctic. The Canadian Regional Climate Model (CRCM): Caya, D., and R. Laprise, 1999: A semi-Lagrangian semi-implicit Regional Climate Model: The Canadian RCM. Mon. Wea. Rev. 127(3), Parameterisation of the land surface processes: the Canadian Land Surface Schema (CLASS) Verseghy, D. L., I. Soil Model. Int. J. of Climatology, 11, Current version: CRCM 4.1 Horizontal resolution: 45 km, CLASS version 2.7 (4.1 m deep, 3 soil layers, 4 major vegetation types) No sub-grid lakes (3D model for Great Lakes only) Offline runoff routing Next version: CRCM 5 Horizontal resolution: 10 km CLASS version 3.3: - Mosaic approach - 9 soil layers - User-defined depth, soil and vegetation types - Permafrost - Inline runoff routing Coupled lake models (for both resolved and sub-grid lakes)

Lakes in Canada 9% of Canada’s surface is covered by lakes. Total: 2 millions lakes of all kinds and sizes. Mountain lakes (Rocky Mountains) Great Lakes Glacial lakes and reservoirs (Canadian shield) Polygonal ponds (permafrost tundra) Lakes influence the regional climate in many ways: thermal moderation, enhanced evaporation, etc. Lakes are influenced by the climate changes. They form an important element of the climate system and have to be included in climate models, used in Canada (as in Scandinavia and in northern Russia) Wetlands (swamps, peatlands)

Coupling of the CRCM model with lake models Steps: Evaluation of available lake models and selection of the best candidate Creation of the high resolution database of Canadian lakes and classification of lakes. Integration of the selected lake model to the CLASS surface scheme Tests and comparisons with analogous coupled models Time range: 2-3 years.

Lake models Only 1D lake models are considered: Horizontal fluxes in lakes are ignored Few input data are required Most kinds of lakes can be simulated Relatively simple Computationally cheap Two 1D lake models are considered: The model of S.W. Hostetler: Hostetler S.W., Bates G.T., Georgi F.,1993: J Geoph. Res., 98(D3), pp Thermal diffusion parameterization in water, snow and ice, multilayered Coupling with RCM : RegCM3, MM4 FLake: - Self-consistent temperature profiles in water, sediment layer and ice - Snow: reduced model: ice albedo parameterization Coupling with RCM : RCA3 Before coupling with the CRCM: evaluation and validation. Off-line with different kinds of lakes, using observation data - in progress Off-line, using data from the CRCM model (reanalysis or simulations without lakes) - in progress On-line with the CRCM model (coupled lake models) The best model will be chosen. Criteria of choice: performance, computing limitations

CRCM resolution: 45 km (current), 10 km (planned) Some lakes are resolved Most lakes are still unresolved – but they are also important for the regional climate. How to deal with unresolved lakes? Exact data on lakes are required → consolidation of different data sources into a common high resolution database is needed. Classification of lakes (example): - Shallow lakes: 0 – 5 m - Intermediate lakes: m - Deep lakes: deeper than 10 m Depths ranges: to be defined A mean depth is associated with each class. If no bathymetry data are available, the class and corresponding average depth are prescribed (intermediate?) Mapping of classified lakes to the model grid: lake classes masks Database of lakes 45 km 10 km Lake Athabasca

CLASS 3.0 and later: mosaic approach Horizontal fluxes on the surface and within the soil are neglected. Vertical fluxes from atmosphere are considered homogenous within model grid cells. On each grid cell fractions of each kind of soil and vegetation are identified. Vertical thermal and water balances are found for each present soil-vegetation combination. Surface conditions are averaged with surface fractions as weights. Lakes are introduced as new kinds of mosaic elements: All lakes within each class on the grid cell are considered as a single lake of the average depth of this class and of the total surface of these lakes. The lake model is applied independently of all lake classes. Resulting surface conditions on lakes and surface elements are averaged with surface fractions as weights. Integration to the surface scheme Shallow lakes Intermediate lakes Deep lakes

Tests and comparisons with other models Validation: coupled vs non-coupled CRCM Comparisons with other coupled models: (RCA3+FLake, RegCM3+Hostetler, etc.) Improved simulation of Canadian climate by the CRCM model – including arctic regions. Better understanding of the lake-atmosphere interactions. Climate change simulations to understand changes to the lake thermal regime and associated feedbacks to the atmosphere Lakes: Lakes over permafrost: non-zero bottom thermal flux, active layer. Improved ice/snow schemes for lakes. “Dynamic lakes”: local water balance, variable water level CLASS: dynamic vegetation CRCM: ocean coupling Expected outcomes Next challenges