Abstract
AbstractGiven the ever increasing spatial resolution of climate models and the significant role of lakes on the regional climate, it becomes important to represent water bodies in climate models. Such developments have started in the IPSL (Institut Pierre Simon Laplace) climate model and its land surface component, ORganizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE), with the Freshwater Lake model, FLake. To answer the questions raised by these new developments, such as the lake differentiation and related model parameters, we analyze spatial distributions of lake characteristics in the whole world to perform a global sensitivity analysis of the FLake parameters. As a result, three different climates and four lake depth configurations were selected as test cases. The Sobol method as sensitivity analysis based on variance decomposition was chosen to rank parameters impact on the model output, that is, lake surface water temperature, latent and sensible heat fluxes. We focus on the 11 parameters of the FLake model, which are the lake depth, the albedo and light extinction coefficient of water, snow, and ice respectively, the fetch, and the relaxation coefficient of the thermocline shape factor. The results show different sensitivity features according to the lake type and climate. The dominant role and time varying contribution of the lake depth, radiative parameters (albedo, light extinction coefficient) and thermocline relaxation coefficient linked to the atmospheric conditions, were clearly highlighted. These findings will lead us to distinguish between different lake categories in each grid cell of ORCHIDEE in the future implementation.
Highlights
Lakes are often neglected in climate modeling because their spatial extent at global scale does not exceed 3.7% of the Earth's non glacial land area (Verpoorter et al, 2014)
We focus on the 11 parameters of the freshwater lake model (FLake) model, which are the lake depth, the albedo and light extinction coefficient of water, snow, and ice respectively, the fetch, and the relaxation coefficient of the thermocline shape factor
For sake of clarity, and because the results do not differ from one year to the other, we only plot the results obtained for the year 2001
Summary
Lakes are often neglected in climate modeling because their spatial extent at global scale does not exceed 3.7% of the Earth's non glacial land area (Verpoorter et al, 2014). The specific properties and physics of lakes (i.e., high heat capacity, low albedo and surface roughness, and water-ice transition phases) explain their major role on local meteorology and boundary layer stratification, as well as their influence on cloud formation (Laird et al, 2009). This has been demonstrated in numerous studies at global scale (Bonan, 1995; Dutra et al, 2010; Krinner, 2003; Mironov et al, 2010) and on the climate of regions where large fractions of land are covered by lakes.
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