Influences of the environment of a wind farm on the forecasts of its power generation using models GFS (50km/3h) and WRF (2km/15min) : The case study of Amel wind farm (High Belgium)

peer reviewedThe economic and climate contexts require to use more electricity from wind farms. However this kind of production is intermittent, therefore it is necessary to forecast this resource at least 1 day ahead. Our laboratory has developed a forecasting model of wind-based electricity generation based on a global meteorological model (GFS) with a resolution of 50 km and 3 h. But this model has a resolution too coarse for a wind farm. So we have configured the regional model WRF with resolution of 2 km and 15 min to obtain better forecasts. Finally, the WRF model provides better forecasts, but both must be adjusted to take into account the direct environment of the wind farm

Analyse du refroidissement après minuit de la température de la chaussée en Wallonie

peer reviewe

Stable climate and surface mass balance in Svalbard over 1979–2013 despite the Arctic warming

With the help of the regional climate model MAR (Modèle Atmosphérique Régional) forced by the ERA-Interim reanalysis (MARERA) and the MIROC5 (Model for Interdisciplinary Research on Climate) global model (MARMIROC5) from the CMIP5 (Coupled Model Intercomparison Project) database, we have modelled the climate and surface mass balance of Svalbard at a 10 km resolution over 1979–2013. The integrated total surface mass balance (SMB) over Svalbard modelled by MARERA is negative (−1.6 Gt yr−1) with a large interannual variability (7.1 Gt) but, unlike over Greenland, there has been no acceleration of the surface melt over the past 35 years because of the recent change in atmospheric circulation bringing northwesterly flows in summer over Svalbard, contrasting the recent observed Arctic warming. However, in 2013, the atmospheric circulation changed to a south–southwesterly flow over Svalbard causing record melt, SMB (−20.4 Gt yr−1) and summer temperature. MIROC5 is significantly colder than ERA-Interim over 1980–2005 but MARMIROC5 is able to improve the near-surface MIROC5 results by simulating not significant SMB differences with MARERA over 1980–2005. On the other hand, MIROC5 does not represent the recent atmospheric circulation shift in summer and induces in MARMIROC5 a significant trend of decreasing SMB (−0.6 Gt yr−2) over 1980–2005

Circulations atmosphériques et anomalies de fonte à la surface de la calotte glaciaire du Groenland

peer reviewedWith the aim to study the impact of the 500hPa general circulation on the Greenland ice sheet surface melt simulated by the regional climate model MAR, we developed a new Circulation Type Classification (CTC) based on the 500hPa geopotential height from the ECMWF (re)analysis over the period 1958-2007. This CTC shows that the dominant mode of the regional atmospheric variability around the Greenland is linked to the North Atlantic Oscillation (NAO) and that the surface anomalies are highly correlated to the general circulation. It explains also why a record surface melt was observed during the summer 2007. The 27th August of 2003, where the temperature was 10°C higher than the normal, is the consequence of an almost unique 500 hPa circulation in the 50 last years.Pour étudier les impacts de la circulation atmosphérique à 500hPa sur la fonte estivale à la surface de la calotte du Groenland simulée par le modèle du climat MAR, nous avons mis au point une nouvelle classification automatique des types de circulations atmosphériques appliquée à la période qui s'étend de 1958 à 2007. Cette classification, basée sur la hauteur géopotentielle à 500hPa issue des (ré)analyses du Centre Européen, permet de montrer que le mode dominant de la variabilité atmosphérique au Groenland est lié à l'Oscillation Nord-Atlantique (NAO) et que la fonte à la surface de la calotte est hautement corrélée à la circulation générale. Cette classification explique pourquoi une fonte record fut enregistrée durant l'été 2007. De même, le caractère exceptionnel du 27 août 2003, où la température moyenne au Groenland était près de 10°C supérieure à la moyenne 1958-2007, est clairement une conséquence d'une circulation à 500hPa presque unique durant les 50 dernières années de l'histoire climatique du Groenland

Do global warming-induced circulation pattern changes affect temperature and precipitation over Europe during summer?

Future climate change projections are not limited to a simple warming, but changes in precipitation and sea level pressure (SLP) are also projected. The SLP changes and the associated atmospheric circulation changes could directly mitigate or enhance potential projected changes in temperature and precipitation associated with rising temperatures. With the aim of analysing the projected circulation changes and their possible impacts on temperature and precipitation over Europe in summer [June–July–August (JJA)], we apply an automatic circulation type classification method, based on daily SLP, on general circulation model (GCM) outputs from the Coupled Model Intercomparison Project phase 5 (CMIP5) database over the historical period (1951–2005) and for climate under two future scenarios (2006–2100). We focus on summer as it is the season when changes in temperature and precipitation have the highest impact on human health and agriculture. Over the historical observed reference period (1960–1999), our results show that most of the GCMs have significant biases over Europe when compared to reanalysis data sets, both for simulating the observed circulation types and their frequencies, as well as for reproducing the intraclass means of the studied variables. The future projections suggest a decrease of circulation types favouring a low centred over the British Isles for the benefit of more anticyclonic conditions. These circulation changes mitigate the projected precipitation increase over north-western Europe in summer, but they do not significantly affect the projected temperature increase and the precipitation decrease over the Mediterranean region and eastern Europe. However, the circulation changes and the associated precipitation changes are tarnished by a high uncertainty among the GCM projections

Approach Flow Depth Influence on Nonlinear Weir Discharge Capacity

The high hydraulic efficiency and the compactness of nonlinear weirs favor their use in several rehabilitation or new dams projects. Main types of nonlinear weirs are labyrinth and piano key weirs.The purpose of this paper is to provide indications on the influence of the approach flow depth on the discharge capacity of these nonlinear weirs. To do so, a series of experimental tests have been carried out in the laboratory of Engineering Hydraulics of the Liege University. A labyrinth and a piano key weir have been tested in channel configuration (upstream flow width equal to the weir width) considering various dimensionless dam heights. A large range of discharge has been tested for each case. The results show that the dimensionless dam height increase may decrease up to 8% of the labyrinth weir discharge capacity while it has only very limited but opposite effects for the piano key weir

Impact of the spatial resolution on the Greenland ice sheet surface mass balance modelling

peer reviewedBy using the regional climate model MAR (Modèle Atmosphérique Régional), 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 projections of the GrIS contribution to sea-level rise over the next 200 years. However, the ice sheet models often run at a higher resolution (typically 5-10km) than the current MAR resolution (25km). 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. 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

Discrimination des effets radiatifs et des effets advectifs à partir des observations de températures du réseau météo-routier de Wallonie

La valeur de la température et son évolution temporelle constituent des éléments majeurs de la caractérisation des types de temps. Elles dépendent bien entendu du milieu dans lequel elles sont mesurées et elles doivent être relativisées en fonction des saisons. Elles intègrent les effets du rayonnement, de l’advection synoptique des masses d’air et des perturbations locales de l’écoulement d’air provoquées par la topographie. Quelques effets radiatifs et advectifs sont mis en évidence à partir de données du réseau de météorologie routière de la région wallonne (Belgique).The temperature value and its temporal variation represent major elements for the characterization of the weather types. These elements depend on the environment, in which they are measured, and the characteristics of the recorded data depend on the seasons. They take into account the radiation effect, the synoptic advection of air masses and the local disturbances of air flow due to topography. Some radiative and advective effects are highlighted with the data of the road meteorological network of the Walloon Region (Belgium)

Modélisation combinée pour améliorer l'étude des structures hydrauliques

peer reviewedaudience: researcher, professionalPhysical modeling and numerical modeling are two efficient analysis approaches in hydraulic engineering. The interactive application of both methods is obviously the more effective response to most flow problems analyses. Indeed, it enables combining the inherent advantages of both approaches, which are complementary, while being beneficial to the delays as well as the quality of the analysis. The paper presents the way composite modeling is applied for years at the HECE - Laboratory of Engineering Hydraulics (University of Liege) to enhance hydraulic structures studies. Besides numerical model validation for which experimental benchmarks constitute the first reliable data source, simultaneous application of both modeling approaches may be envisaged in three different ways. Composite modeling may be used to increase the scale factor of physical models by reducing the layout of the real structure to be modeled, to provide a better answer to specific problems than a single approach study or to maximize the efficiency of experimental tests by reducing the range of variation of the unknown parameters to be tested. For each of these three issues depicted in the paper, several examples show how the combined use of efficient numerical solvers together with physical scale models enables to increase the overall quality and scope of the analyses while decreasing the delays and possibly the costs

A systematic procedure to predict flows induced by major dysfunctions on complexes or cascades of dams

peer reviewedHazard analysis of dams arranged in complex or in cascade may involve the assessment of a large number of different scenarios of combined failures. However, a tremendous computation time would be needed to perform a detailed modeling of the flows generated by all possible scenarios. Therefore, the present paper describes a rational methodology for analyzing the flows induced by the most relevant incidents occurring on a complex or in a cascade of dams and reservoirs. The methodology combines several hydrodynamic models, including the twodimensional flow solver WOLF 2D and a simplified lumped hydrodynamic model, to simulate (i) the flows induced on the dams complex, (ii) the potential breaching in cascade of other dams, as well as (iii) the propagation of the flood wave in the whole downstream valley. The application of the methodology to a practical case study involving a complex of five dams is also described