Stéphane Goyette

Application of the Canadian regional climate model to the Laurentian great lakes region: Implementation of a lake model

Abstract This study reports on the implementation of an interactive mixed‐layer/thermodynamic‐ice lake model coupled with the Canadian Regional Climate Model (CRCM). For this application the CRCM, which uses a grid mesh of 45 km on a polar stereographic projection, 10 vertical levels, and a timestep of 15 min, is nested with the second generation Canadian General Circulation Model (GCM) simulated output. A numerical simulation of the climate of eastern North America, including the Laurentian Great Lakes, is then performed in order to evaluate the coupled model. The lakes are represented by a “mixed layer” model to simulate the evolution of the surface water temperature, and a thermodynamic ice model to simulate evolution of the ice cover. The mixed‐layer depth is allowed to vary spatially. Lake‐ice leads are parametrized as a function of ice thickness based on observations. Results from a 5‐year integration show that the coupled CRCM/lake model is capable of simulating the seasonal evolution of surface temperature and ice cover in the Great Lakes. When compared with lake climatology, the simulated mean surface water temperature agrees within 0.12°C on average. The seasonal evolution of the lake‐ice cover is realistic but the model tends to underestimate the monthly mean ice concentration on average. The simulated winter lake‐induced precipitation is also shown, and snow accumulation patterns on downwind shores of the lakes are found to be realistic when compared with observations.

Spatial Predictions of Extreme Wind Speeds over Switzerland Using Generalized Additive Models

The purpose of this work is to present a methodology aimed at predicting extreme wind speeds over Switzerland. Generalized additive models are used to regionalize wind statistics for Swiss weather stations using a number of variables that describe the main physiographical features of the country. This procedure enables one to present the results for Switzerland in the form of a map that provides the 98th percentiles of daily maximum wind speeds (W98) at a 10-m anemometer height for cells with a 50-m grid interval. This investigation comprises three major steps. First, meteorological data recorded by the weather stations was gathered to build local wind statistics at each station. Then, data describing the topographic and landscape characteristics of the country were prepared using geographic information systems (GIS). Third, appropriate regression models were selected to make spatially explicit predictions of extreme wind speeds in Switzerland. The predictions undertaken in this study provide realistic values of the W98. The effects of topography on the results are particularly conspicuous. Wind speeds increase with altitude and are greatest on mountain peaks in the Alps, as would be intuitively expected. Relative errors between observations and model results calculated for the meteorological stations do not exceed 30%, and only 12 out of 70 stations exhibit errors that exceed 20%. The combination of GIS techniques and statistical models used to predict a highly uncertain variable, such as extreme wind speed, yields interesting results that can be extended to other fields, such as the assessment of storm damage on infrastructures.

Numerical Investigation with a Physically Based Regional Interpolator for Off-Line Downscaling of GCMs: FIZR

Abstract A novel approach for regional climate modeling based on an off-line downscaling of GCM simulations is described and illustrated with a one-month simulation example. The model is physically based and it requires outputs from a previous GCM integration. The methodology is based upon the premise that much of “small-scale” variability (i.e., for spatial scales below current GCM resolution) is often the result of surface forcings rather than small-scale dynamical effects. Following on this consideration, the present work seeks to address the question of regional climate diagnostics by combining precomputed GCM atmospheric large-scale transports of momentum, heat, and moisture, called “the dynamics,” with recomputed GCM subgrid-scale parameterized effect, called “the physics,” including an additional mesoscale forcing term that is parameterized in terms of large-scale flow resolved by GCM coupled with fine-scale geophysical surface fields. This combination is integrated in a prognostic mode on a high-r...

Daytime microclimatic impacts of the SOVALP project in summer: A case study in Geneva, Switzerland

The Société Simple de Valorisation de Terrains à Genève-La Praille (SOVALP) project was conceived as a means of providing adequate housing within redevelopment policies during the last decades in Geneva, Switzerland including, among other measures, ideas for recovering an old industrial site. The SOVALP project is aimed at the construction of a mixed-use urban center around a multimodal hub with a built area around 300,000 m2. The present study analyzes the daytime impacts on outdoor thermal comfort from such an intervention in the urban environment, based on microclimatic field measurements and computer simulations. The microclimatic variables were collected simultaneously at two monitoring points during daytime in August 2011, around the Praille Railway Station. From calculations of the outdoor comfort indices Physiological Equivalent Temperature Index (PET) and Universal Thermal Climate Index (UTCI) derived from field measurements, it was found that the current situation in summer presents a high level of heat stress. By means of the ENVI-met software microclimate simulations, beneficial effects from the SOVALP project arose, pointing to reductions in air temperature as high as 2.2°C within the redeveloped area and of 1.2°C in the entire area evaluated. Changes in PET and UTCI point to a reduction in heat stress categories.

Numerical investigations of extreme winds over Switzerland during 1990-2010 winter storms with the Canadian Regional Climate Model

This study reports on the ability of the Canadian Regional Climate Model to simulate the surface wind gusts of 24 severe mid-latitude storms in Switzerland during the period 1990–2010. A multiple self-nesting approach is used, reaching a final 2-km grid which is centred over Switzerland, a country characterised by complex topography. A physically-based wind gust parameterization scheme is applied to simulate local surface gusts. Model performance is evaluated by comparing simulated wind speeds to time series at weather stations. While a number of simulated variables are reproduced in a realistic manner, the surface wind gusts show differences when compared to observed values. Results indicate that the performance of this parameterization scheme not only depends on the accuracy of the simulated planetary boundary layer, the vertical temperature, wind speed and atmospheric humidity profiles, but also on the accuracy of the reproduction of the surface fields such as temperature and moisture.

Twin climate cities—an exploratory study of their potential use for awareness-raising and urban adaptation

Twin climate cities are pairs of cities for which it is appropriate to assume that the future climate of a city “A” will be significantly similar to the current climate of another city “B”. In this paper, we explore the potential use of the climate twins approach for the development of adaptation strategies to climate change in urban areas. We propose an innovative and robust climate-matching method that is suitable to link cities’ current and future climates. Of the 100 cities investigated, 70 have at least one twin climate region, and 39 have a twin climate city. The case-study revealed a highly significant similarity for temperature variables and heat-related indices, but a less significant similarity for precipitation variables. The Climate Twins approach appears to be a potentially effective mechanism for raising awareness about the pace of climate change and for easily identifying (1) future impacts and vulnerabilities associated with climate change as well as (2) policies, infrastructure, and best practices that should be implemented in a city in order to cope efficiently with future extreme temperature events.

Specification of surface characteristics for use in a high resolution regional climate model: on the role of glaciers in the swiss alps

Certain aspects of the specification of the land cover characteristics for use in high-resolution regional climate models (RCMs) are considered in this paper. We demonstrate the importance of specifying the appropriate surface characteristics at high horizontal resolution and discuss their impacts on the simulated surface prognostic variables, on the surface energy flux as well as on the surface winds in the alpine domain of Switzerland, using the Canadian regional climate model (CRCM). Fixing lower boundary conditions consists in prescribing primary ground characteristics such as land-use (vegetation and soil types and their relative spatial coverage), and the surface height with respect to mean sea level. In the current version of the CRCM land-surface scheme, the land-use serves to fix the surface albedo and the large-scale roughness height, the vegetation type affects the soil water holding capacity, the evapotranspiration efficiency, the snow masking depth, while the soil type determines the soil thermal conductivity and specific heat, thus determining the behaviour of the momentum and sensible heat fluxes, as well as the evapotranspiration at the surface. This in turn may have significant effects on mesoscale circulations. The sensitivity of certain simulated surface fields in the CRCM is assessed through an appropriate specification of glaciers in the Swiss Alps. Until recently, the reference file containing primary ground characteristics was only available at a grid spacing of 1 ° resolution, so its use in high resolution RCMs is inadequate. Modern techniques used in the exploitation of high-resolution geographical data bases combined with existing satellite imagery now enable the resolution of surface characteristics with much improved definition, hence leading to greater confidence on the spatial distribution of the simulated fields computed by the land-surface scheme in RCMs.

Characterization of European cities’ climate shift – an exploratory study based on climate analogues

Purpose Climate analogues have been extensively used in ecological studies to assess the shift of ecoregions due to climate change and the associated impacts on species survival and displacement, but they have hardly been applied to urban areas and their climate shift. This paper aims to use climate analogues to characterize the climate shift of cities and to explore its implications as well as potential applications of this approach. Design/methodology/approach The authors propose a methodology to match the current climate of cities with the future climate of other locations and to characterize cities’ climate shift velocity. Employing a sample of 90 European cities, the authors demonstrate the applicability of this method and characterize their climate shift from 1951 to 2100. Findings Results show that cities’ climate shift follows rather strictly north-to-south transects over the European continent and that the average southward velocity is expected to double throughout the twenty-first century. These rapid shifts will have direct implications for urban infrastructure, risk management and public health services. Originality/value These findings appear to be potentially useful for raising awareness of stakeholders and urban dwellers about the pace, magnitude and dynamics of climate change, supporting identification of the future climate impacts and vulnerabilities and implementation of readily available adaptation options, and strengthening cities’ cooperation within climate-related networks.

Numerical investigation with a coupled single-column lake-atmosphere model: using the Alpert–Stein factor separation methodology to assess the sensitivity of surface interactions

A coupled single-column atmosphere-lake model, along with the Stein–Alpert factor separation methodology, is used to explore some of the non-linear interactions in the vertical dimension between the lower atmosphere and the deep-Lake Geneva, Switzerland, during three selected periods in 1990. The first from the end of April to the end of May when Lake Geneva was building its stratification, the second from mid-August to mid-September during stable stratification, and the third from the end of November to the end of December during destratification. It is recognized that the large thermal inertia of Lake Geneva reduces the surface annual and diurnal temperature variations for neighbouring regions. However, the question of how the open water and the overlying atmosphere interact and which of these “factors” has the most influence needs much attention. The sole presence of the lake is shown to be a major feature with regard to the surface energy budget components whose contributions counteract those of the lower atmosphere, thus supporting the fact that Lake Geneva acts as a damping factor to the regional climate system. It is also shown that not only did the presence of the lake and the overlying atmosphere independently modulate the surface energy budget, but also the synergistic nonlinear interaction among them, either positive or negative, was often found non-negligible. Moreover, some processes may turn out to be important on short time scales while being negligible on the long term.