References of "Erpicum, Michel"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailImpact of the spatial resolution on the Greenland Ice Sheet Surface Mass Balance modelling using the regional climate model MAR with the aim to force an ice sheet model.
Franco, Bruno ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Poster (2011, April 05)

By using the regional climate model MAR (Modèle Atmosphérique Régional), validated for Greenland at 25km resolution and forced every 6 hours with the ERA-INTERIM reanalysis (Fettweis 2007, Fettweis et al ... [more ▼]

By using the regional climate model MAR (Modèle Atmosphérique Régional), validated for Greenland at 25km resolution and forced every 6 hours with the ERA-INTERIM reanalysis (Fettweis 2007, Fettweis et al. 2010), we have modelled the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB) at 20, 25, 30, 40 and 50km resolution to assess the impact of the spatial resolution. As part of the ICE2SEA project, the 25km-resolution SMB outputs of the MAR model are used as forcing fields for ice sheet models, in order to produce future projections of the GrIS contribution to sea-level rise over the next 200 years. Although the current spatial resolution of the MAR model (25km) is much higher than the general circulation models (GCM) resolution (150-300km), the ice sheet models often run at a higher resolution (typically 5-10km). Nevertheless, such higher-resolution runs of the MAR model on the same integration domain generate a significant additional computing time and are not doable until now. Moreover, conventional linear interpolations of the SMB outputs onto a higher-resolution grid, generally induce biases because ice sheet masks at different spatial resolutions do not match and the SMB is a very complex function of the spatial resolution and the topography . That is why several enhanced SMB interpolations are tested here in order to reduce biases when interpolating the MAR outputs onto higher resolution, in the framework of the ICE2SEA project. [less ▲]

Detailed reference viewed: 43 (5 ULg)
Full Text
Peer Reviewed
See detailEvaluation of the present and future general circulation over Greenland simulated by the IPCC AR5/CMIP5 GCMs with the help of a circulation type classification
Belleflamme, Alexandre ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Poster (2011, April 05)

Future projections of the Greenland ice sheet melt are based on General Circulation Model (GCM) simulations. In particular, the reliability of downscaling methods forced by these simulations depends on ... [more ▼]

Future projections of the Greenland ice sheet melt are based on General Circulation Model (GCM) simulations. In particular, the reliability of downscaling methods forced by these simulations depends on the quality of the atmospheric circulation simulated by GCMs. Therefore, it is essential to analyse and evaluate the GCMs modelled general circulation for current climate (1961-1990). Atmospheric circulation type classifications offer a very interesting approach for evaluating the GCM-based circulation at a daily time scale compared to the most used methods based only on monthly means. Indeed, the circulation type classification allows a precise and detailed analysis of each circulation type and so, it gives much more information on the ability of GCMs to simulate the different circulation types and consequently the climatic variability of a region. In fact, exceptional circulation events over Greenland, which cannot be taken into account by the monthly mean approach, have much more impact on the melt than the mean atmospheric state. Thus, an automated correlation-based atmospheric circulation type classification (CTC) is used for evaluating the new GCM outputs (available on http://cmip-pcmdi.llnl.gov/cmip5/) computed for the upcoming IPCC report (AR5). The daily geopotential height at 500 hPa simulations of the GCMs for current climate are compared to the NCEP-NCAR 1 and the ECMWF reanalysis data for the summer months (JJA), when melt is the most important. To achieve this, the classification is first done for the reanalysis data over 1961-1990 and afterwards, the types of the reanalysis based CTC are imposed for classifying the GCM datasets over 1961-1990 (from the historical experiment) to allow a direct type per type comparison based on the frequency distribution of each dataset. This approach also gives the opportunity to study the intraclass repartition differences between the reanalysis and the GCMs. After the evaluation of the GCM simulations for current climate, the future projections driven by RCP concentrations or emissions (2011-2040, 2041-2070 and 2071-2100) from the best matching GCMs are analysed in the same way. For current climate, it clearly appears that only a few GCMs are able to reproduce reliably the variability of the atmospheric circulation over Greenland during summer. The differences of frequency between the GCMs and the reanalysis are mainly due to biases of the geopotential height which is systematically over or underestimated by most GCMs and to the underestimation of the variability of the circulation by most GCMs. For future projections, no new circulation types are detected, but rather a general increase of the mean geopotential height regardless of the circulation type. It is also important to note that for many GCMs, the uncertainty of the current climate simulations (given by the differences of the classification results between the GCM simulations for current climate and the reanalysis data for the same time) are of the same order than the projected changes for future climate. Therefore, these projections may be questionable. [less ▲]

Detailed reference viewed: 64 (10 ULg)
Full Text
Peer Reviewed
See detailEvaluation of the Greenland ice sheet surface mass balance simulated by a regional climate model forced by some selected IPCC AR5/CMIP5 AOGCMs over the current climate.
Fettweis, Xavier ULg; van den Broeke, Michiel; van de Berg, Willem Jan et al

Conference (2011, April 05)

Abstract. As part of the ICE2SEA project, the regional climate model MAR was forced by the general circulation model ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass ... [more ▼]

Abstract. As part of the ICE2SEA project, the regional climate model MAR was forced by the general circulation model ECHAM5 for making future projections of the Greenland Ice Sheet (GrIS) Surface Mass Balance (SMB) over 1980-2099 at a resolution of 25km. For the A1B scenario, MAR projects a highly negative (-500 GT/yr) SMB rate at the end of this century and a induced mass loss corresponding to a sea level rise of ~7 cm over 2000-2100. However, the comparison with MAR forced by the ERA-40 reanalysis over 1980-1999 shows that MAR forced by the 20C3M scenario is not able to represent reliably the current SMB due to biases in the general circulation and in the free atmosphere summer temperature modeled by ECHAM5 around the GrIS. These biases induce in MAR an underestimation of the snow accumulation and an overestimation of the surface melt. Therefore, this questions the reliability of these ECHAM5-forced future projections, knowing that i) these biases could be amplified in future and that ii) the MAR outputs are used to force ice sheets models for the ICE2SEA project. That is why, by waiting the outputs from the next generation of GCMs (CMIP5), we investigate the impacts of current climate biases over the future projections and we suggest corrections of ECHAM5 forcing files for having a better agreement with the ERA-40 forced simulation. This is useful for the ice sheet model wanting to use the absolute values of MAR future projections instead of anomalies. [less ▲]

Detailed reference viewed: 73 (11 ULg)
Full Text
See detailEvolution of wind behaviour and of its potential for wind power production in Belgium during the last 30 years.
Doutreloup, Sébastien ULg; Fettweis, Xavier ULg; Sacré, Bernard ULg et al

Poster (2011, April 04)

The number of wind turbines in the world grows significantly every year due to politics proposing green energy productions as solutions to mitigate climate change effects. However, this kind of energy is ... [more ▼]

The number of wind turbines in the world grows significantly every year due to politics proposing green energy productions as solutions to mitigate climate change effects. However, this kind of energy is dependent on the weather. This implies that the wind production is irregular at a very short time scale. But the short time scale availability of the wind-based energy is important to the producers of energy as well as to the electric grid managers because the wind energy production can rise or fall rapidly which creates some financial and voltage variations. For these reasons, we study the past evolution of the availability of the wind quantity by analysing the intermittence of the wind speed in Belgium during the last 30 years. To reach this goal, we use the regional model WRF (Weather and Research Forecast model) developed by the UCAR community users. The WRF model is forced by the NCEP2 Reanalysis model to obtain a regionalisation of the weather conditions over a domain centred on Belgium at a spatiotemporal resolution of 10 km and 1 min. This resolution allows to capture the minute-based time scale variability of wind speed and consequently the irregular behaviour of the wind power production. To obtain a value of the wind intermittence, we calculate the persistence of a wind blowing continuously with a minimum speed of 1 ms-1, then the persistence of a wind blowing continuously with a minimum speed of 2 ms-1, etc. The persistence of the wind speed and its evolution over 30 years are characterised by : (a) the mean wind speed over a fixed period (monthly, seasonally, … ), (b) the mean duration of a wind speed above x ms-1 over the same fixed period and (c) the evolution of (a) and (b) during the studied period. This study will show the evolution during the last decades of the wind behaviour in Belgium and its potential for electricity production. [less ▲]

Detailed reference viewed: 55 (8 ULg)
Full Text
Peer Reviewed
See detailPresent and future climates of the Greenland ice sheet according to the IPCC AR4 models
Franco, Bruno ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg et al

in Climate Dynamics (2011), 36

The atmosphere–ocean general circulation models (AOGCMs) used for the IPCC 4th Assessment Report (IPCC AR4) are evaluated for the Greenland ice sheet (GrIS) current climate modelling. The most suited ... [more ▼]

The atmosphere–ocean general circulation models (AOGCMs) used for the IPCC 4th Assessment Report (IPCC AR4) are evaluated for the Greenland ice sheet (GrIS) current climate modelling. The most suited AOGCMs for Greenland climate simulation are then selected on the basis of comparison between the 1970–1999 outputs of the Climate of the twentieth Century experiment (20C3M) and reanalyses (ECMWF, NCEP/NCAR). This comparison indicates that the representation quality of surface parameters such as temperature and precipitation are highly correlated to the atmospheric circulation (500 hPa geopotential height) and its interannual variability (North Atlantic oscillation). The outputs of the three most suitable AOGCMs for present-day climate simulation are then used to assess the changes estimated by three IPCC greenhouse gas emissions scenarios (SRES) over the GrIS for the 2070–2099 period. Future atmospheric circulation changes are projected to dampen the zonal flow, enhance the meridional fluxes and therefore provide additional heat and moisture to the GrIS, increasing temperature over the whole ice sheet and precipitation over its northeastern area. We also show that the GrIS surface mass balance anomalies from the SRES A1B scenario amount to −300 km3/year with respect to the 1970–1999 period, leading to a global sea-level rise of 5 cm by the end of the 21st century. This work can help to select the boundaries conditions for AOGCMs-based downscaled future projections. [less ▲]

Detailed reference viewed: 115 (33 ULg)
Full Text
See detailEvaluation over Greenland of WRF with GC-NET observations (1995-2005) by comparison with 2 other RCMs
Sacré, Bernard ULg; Fettweis, Xavier ULg; Doutreloup, Sébastien ULg et al

Conference (2011)

In the context of climate change, the Greenland Ice Sheet (GrIS) plays an important role in sea level variation and oceanic thermohaline circulation changes. Unfortunately, Global Climate Models do not ... [more ▼]

In the context of climate change, the Greenland Ice Sheet (GrIS) plays an important role in sea level variation and oceanic thermohaline circulation changes. Unfortunately, Global Climate Models do not illustrate enough the characteristics of Greenland. To solve that, specific RCMs have been developed to take into account the features of polar regions. In this project, we compare three RCMs : the MAR model, the RACMO model and the Weather Research and Forecasting (WRF) model. WRF is an open source model developed by the Mesoscale and Microscale Meteorology Division of NCAR. We use here the standard WRF (version 3.2.1) and its polar optimization (called polar WRF). The MAR version tuned for the GrIS and coupled with a 1D surface scheme called SISVAT (for Soil Ice Snow Vegetation Atmosphere Transfer) is compared here. The version of RACMO is a specific version for the Greenland climate, RACMO2/GR. This model contains a special surface module for snow-ice treatment and other modifications concerning, for example, the surface turbulence heat flux or the surface roughness. The comparison is made on a domain centered on Greenland at a 25-km horizontal resolution over the 1995-2005 period when Automatic Weather Station (AWS) measurements are available from the Greenland Climate NETwork (GC-NET). Statistics (mean, bias, RMSE, correlation coefficient) are calculated for the near-surface temperature, surface pressure, 10m-wind speed and specific humidity for winter (October to April) and summer (May to September). In addition, the modeled snowfall are evaluated with ice core-based snow accumulation climatologies. Comparison shows a significant improvement from RCMs compared to the reanalyses (NCEP2 and ERA-INTERIM) in respect to the AWS measurements. RACMO and MAR seem to compare better with observations than WRF. [less ▲]

Detailed reference viewed: 58 (7 ULg)
Full Text
Peer Reviewed
See detailThe 1958–2009 Greenland ice sheet surface melt and the mid-tropospheric atmospheric circulation
Fettweis, Xavier ULg; Mabille, Georges; Erpicum, Michel ULg et al

in Climate Dynamics (2011), 36(1 (2011)), 139-159

In order to assess the impact of the mid-tropospheric circulation over the Greenland ice sheet (GrIS) on surface melt, as simulated by the regional climate model MAR, an automatic Circulation type ... [more ▼]

In order to assess the impact of the mid-tropospheric circulation over the Greenland ice sheet (GrIS) on surface melt, as simulated by the regional climate model MAR, an automatic Circulation type classification (CTC) based on 500 hPa geopotential height from reanalyses is developed. General circulation correlates significantly with the surface melt anomalies for the summers in the period 1958–2009. The record surface melt events observed during the summers of 2007–2009 are linked to the exceptional persistence of atmospheric circulations favouring warm air advection. The CTC emphasizes that summer 500 hPa circulation patterns have changed since the beginning of the 2000s; this process is partly responsible for the recent warming observed over the GrIS. [less ▲]

Detailed reference viewed: 106 (34 ULg)
Full Text
See detailUsing a circulation type classification to analyse the general circulation over Greenland simulated by GCMs
Belleflamme, Alexandre ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Conference (2010, November 23)

Future projections of the Greenland ice sheet melt are mainly based on General Circulation Model (GCM) outputs. The atmospheric circulation type classification offers a unique opportunity for validating ... [more ▼]

Future projections of the Greenland ice sheet melt are mainly based on General Circulation Model (GCM) outputs. The atmospheric circulation type classification offers a unique opportunity for validating the GCM-based circulations. Six GCMs used in the last IPCC report are analysed here. A correlation-based classification is constructed for each model using daily geopotential height at 500 hPa over Greenland. It is applied to a dataset combining the GCM-based outputs (20C3M scenario) for the current climate and the NCEP-NCAR 1 reanalysis data over the period 1961-1990 allowing a direct comparison for each circulation type. Most of the analysed models are able to reproduce the main circulation types, but they fail to reproduce their frequencies because they underestimate the climate variability. In addition, some biases in the mean geopotential height remain. However, we use our atmospheric circulation type classification for analysing future projections made by GCMs. As for the 20th century climate, a combined classification is made integrating reanalysis data over 1971-1990, GCM-based outputs over 1971-1990 (using 20C3M scenario) and GCM-based outputs over 2046-2065 and 2081-2100 (using A1B scenario). No new circulation types are individualised knowing that the main changes are just a general increase of the geopotential height. Furthermore, the changes in frequency observed between the 20th century climate and the first future period (2046-2065) are of the same order than the uncertainties of the models for simulating the current climate by comparison with the reanalysis data. Therefore, the circulation type classification is a useful tool to give a precise analysis of the atmospheric circulation simulated by GCMs knowing that most of downscaling techniques are dependent on the general circulation simulated by the GCMs. [less ▲]

Detailed reference viewed: 32 (4 ULg)
Full Text
Peer Reviewed
See detailHigh resolution modelling of the Greenland ice sheet surface mass balance using the regional climate model MAR coupled with a downscaling interface
Franco, Bruno ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Poster (2010, November 05)

We are developing a coupling interface downscaling the 25km-atmosphere fields simulated by the regional climate MAR (Modèle Atmosphérique Régional) model onto a 5km-grid in order to resolve the surface ... [more ▼]

We are developing a coupling interface downscaling the 25km-atmosphere fields simulated by the regional climate MAR (Modèle Atmosphérique Régional) model onto a 5km-grid in order to resolve the surface processes at high resolution with the SISVAT (Sea Ice Soil Vegetation Atmosphere Transfer) snow-ice module. This coupling interface improves the representation of the topography and ablation zone of the Greenland ice sheet (GrIS) in the MAR model, and therefore will provide higher resolution estimations of the GrIS surface mass balance (SMB) without additional computing time. By using outputs from previously-gauged global circulation models (GCM) as forcing fields, the MAR model coupled with the downscaling interface will then perform 5km future simulations of the GrIS SMB for different IPCC greenhouse gas emissions scenarios for the 21st century. [less ▲]

Detailed reference viewed: 32 (4 ULg)
Full Text
See detailAnalysis of the atmospheric circulation simulated by GCMs over Greenland
Belleflamme, Alexandre ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Conference (2010, November 05)

The variability of the geopotential height at 500 hPa simulated by General Circulation Models (GCMs) over Greenland is evaluated using an atmospheric circulation type classification. The GCM outputs for ... [more ▼]

The variability of the geopotential height at 500 hPa simulated by General Circulation Models (GCMs) over Greenland is evaluated using an atmospheric circulation type classification. The GCM outputs for the current climate (20C3M) are first compared to reanalysis data over 1961-1990. The comparison shows that most of them simulate well the main circulation types but fail to reproduce their frequencies because of underestimations of circulation variability and biases in the mean geopotential height. GCM-based future projections do not individualise new circulation types but show a general increase of the geopotential height. Based on this approach, the correlation between surface temperature and atmospheric circulation offers a new way for estimating the Greenland ice sheet melt. [less ▲]

Detailed reference viewed: 43 (14 ULg)
Full Text
Peer Reviewed
See detailInterests of regional modelisation for wind power forecasting
Doutreloup, Sébastien ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg

Conference (2010, October 22)

European policies have decided to reduce the greenhouse gas emissions of 20% and to reach 20% of renewable power production by 2020. Increasing wind power is one of the numerous solutions to reach these ... [more ▼]

European policies have decided to reduce the greenhouse gas emissions of 20% and to reach 20% of renewable power production by 2020. Increasing wind power is one of the numerous solutions to reach these goals. However, this kind of energy production depends on the meteorological conditions and gives it an intermittent behaviour. The wind speed variations cause voltage and frequency fluctuations that are unacceptable for the power grid. Therefore, forecasting production will become essential with the aim of integrating this kind of energy production into the power grid. We have developed and compared two forecasting models which give as outputs the wind power production every 15 minutes over the Belgian territory: the first one uses the outputs from the global model GFS (available at a horizontal resolution of 0.5° every 3h) and the second one uses the regional climate model WRF-NMM (using a horizontal resolution of 4km). Both of these models predict the wind speed and transform wind speed into wind power production, using a power curve which depends on the wind turbines and their characteristics. The first model using the GFS outputs is not precise enough in space and time to correctly forecast the wind speed in punctual wind farms. That is why we apply some specific tunings on these forecasts. These tunings depend on the air density, the wind direction and the stability of the air mass. The second model using the WRF-NMM outputs runs over the Belgian territory. Initial conditions are forced by the GFS outputs at 0.5° and WRF computes a physical based spatio-temporal downscaling of the meteorological variables. The outputs have a spatial resolution of 4 km and a time resolution of 15 minutes. Some tunings are also needed to adjust the wind power forecasts by comparison to the wind power observations. We present here some results of both models and the interest of using a regional model for more precise wind power forecasting. [less ▲]

Detailed reference viewed: 58 (8 ULg)
Full Text
Peer Reviewed
See detailA statistical validation for the cycles found in air temperature data using a Morlet wavelet-based method
Nicolay, Samuel ULg; Mabille, Georges ULg; Fettweis, Xavier ULg et al

in Nonlinear Processes in Geophysics (2010), 17

Recently, new cycles, associated with periods of 30 and 43 months, respectively, have been observed by the authors in surface air temperature time series, using a wavelet-based methodology. Although many ... [more ▼]

Recently, new cycles, associated with periods of 30 and 43 months, respectively, have been observed by the authors in surface air temperature time series, using a wavelet-based methodology. Although many evidences attest the validity of this method applied to climatic data, no systematic study of its efficiency has been carried out. Here, we estimate confidence levels for this approach and show that the observed cycles are significant. Taking these cycles into consideration should prove helpful in increasing the accuracy of the climate model projections of climate change and weather forecast. [less ▲]

Detailed reference viewed: 87 (18 ULg)
Full Text
See detailMulti-Months Cycles Observed in Climatic Data
Nicolay, Samuel ULg; Mabille, Georges ULg; Fettweis, Xavier ULg et al

in Simard, Suzanne (Ed.) Climate Change and Variability (2010)

Climatic variations happen at all time scales and since the origins of these variations are usually of very complex nature, climatic signals are indeed chaotic data. The identification of the cycles ... [more ▼]

Climatic variations happen at all time scales and since the origins of these variations are usually of very complex nature, climatic signals are indeed chaotic data. The identification of the cycles induced by the natural climatic variability is therefore a knotty problem, yet the knowing of these cycles is crucial to better understand and explain the climate (with interests for weather forecasting and climate change projections). Due to the non-stationary nature of the climatic time series, the simplest Fourier-based methods are inefficient for such applications (see e.g. Titchmarsh (1948)). This maybe explains why so few systematic spectral studies have been performed on the numerous datasets allowing to describe some aspects of the climate variability (e.g. climatic indices, temperature data). However, some recent studies (e.g. Matyasovszky (2009); Paluš & Novotná (2006)) show the existence of multi-year cycles in some specific climatic data. This shows that the emergence of new tools issued from signal analysis allows to extract sharper information from time series. Here, we use a wavelet-based methodology to detect cycles in air-surface temperatures obtained from worldwide weather stations, NCEP/NCAR reanalysis data, climatic indices and some paleoclimatic data. This technique reveals the existence of universal rhythms associated with the periods of 30 and 43 months. However, these cycles do not affect the temperature of the globe uniformly. The regions under the influence of the AO/NAO indices are influenced by a 30 months period cycle, while the areas related to the ENSO index are affected by a 43 months period cycle; as expected, the corresponding indices display the same cycle. We next show that the observed periods are statistically relevant. Finally, we consider some mechanisms that could induce such cycles. This chapter is based on the results obtained in Mabille & Nicolay (2009); Nicolay et al. (2009; 2010). [less ▲]

Detailed reference viewed: 76 (14 ULg)
Full Text
Peer Reviewed
See detailCOST733CAT - a database of weather and circulation
Philipp, Andreas; Bartholy, Judit; Beck, Christoph et al

in Physics & Chemistry of the Earth - Parts A/B/C (2010), 35(9-12), 360-373

Detailed reference viewed: 176 (13 ULg)
Full Text
See detailEtude et modélisation des impacts hydrologiques de pluies exceptionnelles dans un environnement valloné et boisé
Deliège, Jean-François ULg; Erpicum, Michel ULg; Dassargues, Alain ULg et al

Scientific conference (2009, September)

Le jeudi 29 mai 2008 a eu lieu en région liégeoise un événement pluvieux extrême qui a eu des conséquences (humaines et financières) douloureuses. Pour rappel, une pluie de courte durée, mais très intense ... [more ▼]

Le jeudi 29 mai 2008 a eu lieu en région liégeoise un événement pluvieux extrême qui a eu des conséquences (humaines et financières) douloureuses. Pour rappel, une pluie de courte durée, mais très intense (lame d’eau d’environ 90 litres par mètre carré en moins de 2 heures) sur le domaine du Sart Tilman a provoqué des inondations très soudaines (communément appelées « flash-floods ») aux abords des ruisseaux descendant du Sart Tilman vers la Meuse et l’Ourthe. Des évènements du même type ont eu lieu dans les semaines suivantes en région liégeoise (Remicourt, …). La méthodologie développée lors cette étude devait donc être transférable à d’autres applications. Le choix du Sart Tilman comme cas d’étude s’imposait cependant vu la bonne connaissance préliminaire du site par les équipes de l’ULg et la concentration des phénomènes extrêmes. Un tel évènement interpelle et amène à chercher à comprendre le phénomène, à le reproduire de façon théorique et à l’anticiper. Ainsi, à l’initiative de la Ministre de la recherche scientifique de la Communauté Française (Marie-Dominique Simonet), l’Aquapôle a fédéré un travail multidisciplinaire visant à décrire les mécanismes de ces événements extrêmes et à reproduire les impacts hydrologiques de ces pluies exceptionnelles à l’échelle locale, dans un environnement boisé et vallonné. Un des objectifs principaux de ce travail était d’obtenir une méthodologie incluant un modèle intégré permettant d’abord de représenter l’évènement, puis par la simulation de scénarios de tester l’effet spécifique de certains facteurs. En effet, outre la complexité de la dynamique météorologique qui les a générés (ces événements exceptionnels ont présenté des caractéristiques homogènes mais à une échelle très locale), les conséquences de l’évènement ont été le fruit de la combinaison complexe d’une série de facteurs environnementaux et humains : nature des sols, topographie locale, couverture végétale, ouvrages anthropiques et urbanisation, etc. De plus, pour effectuer une modélisation hydrologique physiquement basée et spatialement distribuée, il est nécessaire de disposer de nombreuses informations issues de sources différentes. L’approche pluridisciplinaire exigée pour la rencontre de ces phénomènes a pu être rapidement appréhendée à l’Aquapôle de l’Université de Liège. En particulier, l’existence de modèles compartimentaux intégrés a permis de tenir compte de la dynamique des bassins versants, de la nature hydrogéologique des sols et de la complexité des écoulements de surface et/ou sur l’axe hydraulique. Cette approche de modélisation opérationnelle et pragmatique a tout d’abord nécessité la collecte et la préparation d’un grand nombre de données (dans les environnements cartographiques appropriés) afin d’alimenter les modèles et de créer des bases de données. Ce volet a impliqué un noyau d’équipes composées de topo-climatologues, de topographes, d’hydrauliciens, d’hydrogéologues et d’intégrateurs numériques de façon à prendre en considération l’ensemble des processus et paramètres pertinents à l’atteinte de l’objectif visé. Sur base de la description des processus et de leurs dynamiques spatiale et temporelle ayant abouti à ces catastrophes, l’Aquapôle a pu reproduire et mettre en évidence les événements grâce à des outils de simulations numériques s’appuyant sur une description fine de la météorologie et de la topographie locale, des ouvrages d’art existants et des spécificités locales de toute nature (anthropiques et naturelles). Le dernier volet de cette étude a été dédié à l’élaboration intégrée de scénarios de simulation pour l’utilisation du modèle WOLF HYDRO : un modèle hydrologique spatialement et temporellement distribué qui est principalement développé pour représenter les transferts quasi horizontaux prépondérants en périodes de crues. Son approche physiquement basée lui permet d’utiliser au mieux les différentes informations disponibles. Il a été utilisé dans cette étude, en s’appuyant sur les informations générées par les autres équipes. Pour les trois bassins versants étudiés, de caractéristiques sensiblement différentes, la méthodologie employée permet d’aboutir à des hydrogrammes réalistes pour l’épisode du 29 mai 2008. Des scénarios multiples ont également permis de vérifier la sensibilité du modèle, de tester l’influence d’aménagements potentiels sur le bassin versant (changements d’occupation des sols, création de bassins d’orage, …) et de fournir des résultats pour des pluies de récurrences fixées d’une durée proche de l’événement principal. Les observations réalisées lors de l’événement et les résultats de la modélisation permettent de conclure au fait que l’événement de mai 2008 est véritablement extrême et qu’aucun équipement raisonnable n’aurait pu aboutir à un affaiblissement significatif des débits observés aux exutoires des ruisseaux. Les pics de crues sont en effet parfois proches du double de ceux observés pour une crue bi-centennale. Ainsi, lors d’un tel événement, seul un aménagement prudent de l’habitat aux abords des ruisseaux peut amener à une réduction des dommages matériels. En effet, la délivrance de permis d’urbanisme sur le cours d’eau ou à son voisinage immédiat aggrave les conséquences de ces phénomènes exceptionnels. Enfin, conformément à la notification du Gouvernement Wallon (séance du 3 juin 2009), les résultats de la recherche FL², confiée par la Communauté Française à l’ULg, seront intégrés dans les travaux du GTI (Groupe Transversal Inondations). Ces résultats ont fait l’objet d’une présentation collégiale au GTI le 5 octobre 2009 et d’une présentation à destination des communes et d’un public large et ouvert le 19 novembre 2009. [less ▲]

Detailed reference viewed: 109 (24 ULg)
Full Text
See detailEtude et modélisation des impacts hydrologiques de pluies exceptionnelles dans un environnement vallonné et boisé
Deliège, Jean-François ULg; Erpicum, Michel ULg; Dassargues, Alain ULg et al

Report (2009)

Le jeudi 29 mai 2008 a eu lieu en région liégeoise un événement pluvieux extrême qui a eu des conséquences (humaines et financières) douloureuses. Pour rappel, une pluie de courte durée, mais très intense ... [more ▼]

Le jeudi 29 mai 2008 a eu lieu en région liégeoise un événement pluvieux extrême qui a eu des conséquences (humaines et financières) douloureuses. Pour rappel, une pluie de courte durée, mais très intense (lame d’eau d’environ 90 litres par mètre carré en moins de 2 heures) sur le domaine du Sart Tilman a provoqué des inondations très soudaines (communément appelées « flash-floods ») aux abords des ruisseaux descendant du Sart Tilman vers la Meuse et l’Ourthe. Des évènements du même type ont eu lieu dans les semaines suivantes en région liégeoise (Remicourt, …). La méthodologie développée lors cette étude devait donc être transférable à d’autres applications. Le choix du Sart Tilman comme cas d’étude s’imposait cependant vu la bonne connaissance préliminaire du site par les équipes de l’ULg et la concentration des phénomènes extrêmes. Un tel évènement interpelle et amène à chercher à comprendre le phénomène, à le reproduire de façon théorique et à l’anticiper. Ainsi, à l’initiative de la Ministre de la recherche scientifique de la Communauté Française (Marie-Dominique Simonet), l’Aquapôle a fédéré un travail multidisciplinaire visant à décrire les mécanismes de ces événements extrêmes et à reproduire les impacts hydrologiques de ces pluies exceptionnelles à l’échelle locale, dans un environnement boisé et vallonné. Un des objectifs principaux de ce travail était d’obtenir une méthodologie incluant un modèle intégré permettant d’abord de représenter l’évènement, puis par la simulation de scénarios de tester l’effet spécifique de certains facteurs. En effet, outre la complexité de la dynamique météorologique qui les a générés (ces événements exceptionnels ont présenté des caractéristiques homogènes mais à une échelle très locale), les conséquences de l’évènement ont été le fruit de la combinaison complexe d’une série de facteurs environnementaux et humains : nature des sols, topographie locale, couverture végétale, ouvrages anthropiques et urbanisation, etc. De plus, pour effectuer une modélisation hydrologique physiquement basée et spatialement distribuée, il est nécessaire de disposer de nombreuses informations issues de sources différentes. L’approche pluridisciplinaire exigée pour la rencontre de ces phénomènes a pu être rapidement appréhendée à l’Aquapôle de l’Université de Liège. En particulier, l’existence de modèles compartimentaux intégrés a permis de tenir compte de la dynamique des bassins versants, de la nature hydrogéologique des sols et de la complexité des écoulements de surface et/ou sur l’axe hydraulique. Cette approche de modélisation opérationnelle et pragmatique a tout d’abord nécessité la collecte et la préparation d’un grand nombre de données (dans les environnements cartographiques appropriés) afin d’alimenter les modèles et de créer des bases de données. Ce volet a impliqué un noyau d’équipes composées de topo-climatologues, de topographes, d’hydrauliciens, d’hydrogéologues et d’intégrateurs numériques de façon à prendre en considération l’ensemble des processus et paramètres pertinents à l’atteinte de l’objectif visé. Sur base de la description des processus et de leurs dynamiques spatiale et temporelle ayant abouti à ces catastrophes, l’Aquapôle a pu reproduire et mettre en évidence les événements grâce à des outils de simulations numériques s’appuyant sur une description fine de la météorologie et de la topographie locale, des ouvrages d’art existants et des spécificités locales de toute nature (anthropiques et naturelles). Le dernier volet de cette étude a été dédié à l’élaboration intégrée de scénarios de simulation pour l’utilisation du modèle WOLF HYDRO : un modèle hydrologique spatialement et temporellement distribué qui est principalement développé pour représenter les transferts quasi horizontaux prépondérants en périodes de crues. Son approche physiquement basée lui permet d’utiliser au mieux les différentes informations disponibles. Il a été utilisé dans cette étude, en s’appuyant sur les informations générées par les autres équipes. Pour les trois bassins versants étudiés, de caractéristiques sensiblement différentes, la méthodologie employée permet d’aboutir à des hydrogrammes réalistes pour l’épisode du 29 mai 2008. Des scénarios multiples ont également permis de vérifier la sensibilité du modèle, de tester l’influence d’aménagements potentiels sur le bassin versant (changements d’occupation des sols, création de bassins d’orage, …) et de fournir des résultats pour des pluies de récurrences fixées d’une durée proche de l’événement principal. Les observations réalisées lors de l’événement et les résultats de la modélisation permettent de conclure au fait que l’événement de mai 2008 est véritablement extrême et qu’aucun équipement raisonnable n’aurait pu aboutir à un affaiblissement significatif des débits observés aux exutoires des ruisseaux. Les pics de crues sont en effet parfois proches du double de ceux observés pour une crue bi-centennale. Ainsi, lors d’un tel événement, seul un aménagement prudent de l’habitat aux abords des ruisseaux peut amener à une réduction des dommages matériels. En effet, la délivrance de permis d’urbanisme sur le cours d’eau ou à son voisinage immédiat aggrave les conséquences de ces phénomènes exceptionnels. Enfin, conformément à la notification du Gouvernement Wallon (séance du 3 juin 2009), les résultats de la recherche FL², confiée par la Communauté Française à l’ULg, seront intégrés dans les travaux du GTI (Groupe Transversal Inondations). Ces résultats ont fait l’objet d’une présentation collégiale au GTI le 5 octobre 2009 et d’une présentation à destination des communes et d’un public large et ouvert le 19 novembre 2009. [less ▲]

Detailed reference viewed: 121 (45 ULg)
Full Text
Peer Reviewed
See detailCycles in the Temperature Data Are Induced by the Sun
Nicolay, Samuel ULg; Mabille, Georges ULg; Fettweis, Xavier ULg et al

Poster (2009, April)

The presence of two cycles of period of 30 and 42 months approximatively has been observed in temperature records and climatic indices. Moreover, it has been shown that these cycles are statistically ... [more ▼]

The presence of two cycles of period of 30 and 42 months approximatively has been observed in temperature records and climatic indices. Moreover, it has been shown that these cycles are statistically significant. Here we outline the role played by the Sun in the presence of these cycles, observed in time series. To do so, we use IPCC AR4 climatic models, sunspot number data and the Morlet wavelet method. [less ▲]

Detailed reference viewed: 25 (6 ULg)
Full Text
Peer Reviewed
See detailConfidence Levels for the Cycles Found in Air Temperature Data
Mabille, Georges ULg; Fettweis, Xavier ULg; Erpicum, Michel ULg et al

Poster (2009, April)

Recently, new cycles have been observed in air temperature data and proxy series using a wavelet-based methodology. Although many evidences attest the validity of this method applied to climatic data, no ... [more ▼]

Recently, new cycles have been observed in air temperature data and proxy series using a wavelet-based methodology. Although many evidences attest the validity of this method applied to climatic data, no systematic study of its efficiency has been carried out. Here, we estimate the confidence levels for this approach and show that the observed cycles are significant. [less ▲]

Detailed reference viewed: 31 (5 ULg)