Plus de pluie, mais pas plus d'inondations ...

Le GIEC prévoit pour le futur plus de précipitations et donc plus d'inondations en Belgique. Cependant, en Ardenne, la majorité des débordements de rivières, telles que l'Ourthe, survient en hiver et près de la moitié d'entre eux est due à la combinaison fortes pluies/fonte rapide de la neige. Une reconstitution de l'évolution des précipitations et de l'enneigement en Belgique à l'aide du modèle climatique MAR, développé au Laboratoire de Climatologie de l'ULg, montre que les conditions hydroclimatiques favorisant les inondations hivernales ont diminué en Ardenne au cours de ces cinquante dernières années. La raison ? Une diminution significative de l'accumulation neigeuse et de la durée de la saison d'enneigement. Dans le futur, cette diminution de l'enneigement pourrait ainsi contrebalancer l'augmentation annoncée des précipitations de sorte qu'il n'y aurait pas plus d'inondations en hiver qu'actuellement

Changement climatique : conséquences en Ardenne

Le GIEC (Groupe d'experts Intergouvernemental sur l'évolution du climat) prévoit pour le futur plus de précipitations hivernales et donc à priori un risque accru d'inondations en Belgique. En Ardenne, la majorité des débordements de rivières, telles que l'Ourthe, l'Amblève ou encore la Vesdre, survient en hiver et près de la moitié d'entre eux est due à la combinaison de fortes pluies à une fonte rapide du manteau neigeux. Une reconstitution de l'évolution des précipitations et de l'enneigement en Belgique à l'aide d'un modèle du climat, développé au Laboratoire de Climatologie de l'Université de Liège, montre cependant que les conditions climatiques favorisant les inondations hivernales ont diminué en Ardenne au cours de ces cinquante dernières années

Decrease in hydroclimatic conditions generating floods in the southeast of Belgium over the last 50 years

As a consequence of climate change, several studies concluded that winter flood occurrence could increase in the future in many rivers of northern and western Europe in response to an increase in extreme precipitation events. This study aims to determine if trends in extreme hydroclimatic events generating floods can already be detected over the last century. In particular, we focus on the Ourthe River (southeast of Belgium) which is one of the main tributaries of the Meuse River with a catchment area of 3500 km² . In this river, most of the floods occur during winter and about 50% of them are due to rainfall events associated with the melting of the snow which covers the Ardennes during winter. In this study, hydroclimatic conditions favourable to floods were reconstructed over the period 1959-2010 using the regional climate model MAR (“Modèle Atmosphérique Régional”) forced by the following reanalyses: the ERA-20C, the ERA-Interim and the NCEP/NCAR-v1. The use of the MAR model allows to compute precipitation, snow depth and run-off resulting from precipitation events and snow melting in any part of the Ourthe river catchment area. Therefore, extreme hydroclimatic events, namely extreme run-off events, which could potentially generate floods, can be reconstructed using the MAR model. As validation, the MAR results were compared to weather station-based data. A trend analysis was then performed in order to study the evolution of conditions favourable to flooding in the Ourthe River catchment. The results show that the MAR model allows the detection of about 90% of the hydroclimatic conditions which effectively generated observed floods in the Ourthe River over the period 1974-2010. Whatever the reanalysis used to force the MAR model, the conditions favourable to floods due to snowpack melting combined with rainfall events present a significant negative trend over the last 50 years as a result of a decrease in snow accumulation. However, regarding the conditions favourable to floods due to rainfall events alone, the signal of the trend depends on the reanalysis used to force the model

An Internet agent for language model construction

A software agent is described which is able to take a seed (reference) corpus specified by the user, search the Internet for documents which are sufficiently similar to the seed corpus (as defined by a set of similarity metrics operating at a number of levels in the text), and augment the seed corpus with these documents. The size of the corpus and, hopefully, the quality of the derived language model, are thus progressively increased. The seed corpus may be quite a small collection of transcripts from the application domain, such as may be collected with minimal effort. Preliminary results are given for the perplexity of language models constructed using this approach. Potentially, our method has applications well beyond speech recognition, in corpus-based language processing in general, and document retrieval

Assessing the future evolution of climate extremes favouring floods using the regional climate model MAR over the CORDEX.be domain

In Belgium, most flooding events occur in winter as a result of intense precipitation events but also to the abrupt melting of the snow that covers the Ardennes summits. These conditions favourable to floods exhibit a decreasing trend over the period 1959–2010 resulting from the reduction in snow accumulation thought extreme precipitation events show a positive but non-significant signal. In this study, we investigate how these trends could evolve in a warmer climate by using future projections performed with the regional climate model MAR (for “Modèle Atmosphérique Régional”) in the framework of CORDEX.be, the Belgian EURO-CORDEX project. These future projections were obtained by nesting MAR into NorESM1-M and MIROC5 under the RCP8.5 scenario. Both these global models were selected from the CMIP5 archive after evaluation of their ability to represent the current (1976-2005) mean climate over Europe. This assessment is based on the skill score methodology. Results show that the period 2071-2100 would be marked by a decrease in snowfall amount, in snow accumulation, and consequently in conditions favourable to floods generated by snowpack melting with respect to 1976-2005. Regarding total PPN amount and extremes, the signal is less clear as both GCMs simulate different patterns and trends

An intelligent WWW agent for similarity-based searching

This paper describes the development of a WWW agent that uses similarity-based methods to search the Internet. The Internet Information Agent (IIA) works by analysing a sample of the type of text that is known to be of interest to the user. It then extracts a number of linguistic features and stores these as a feature vector that is used to describe the content of the document. This data is then used as input to a range of similarity metrics that allow the agent to compare new texts with the original and thereby acquire "more of the same". The agent's strengths lie in its use of a range of similarity metrics that are known to perform well over a wide variety of input. The agent has been tested across a range of input data and evaluated against a number of criteria. The results of this evaluation are described and the prospects for the ongoing development of the agent are discussed

Information retrieval system and method that generates weighted comparison results to analyze the degree of dissimilarity between a reference corpus and a candidate document

An internet information agent accepts a reference document, performs an analysis upon it in accordance with metrics defined by its analysis algorithm and obtains respective lists (word, character-level n-gram, word-level n-gram), derives weights corresponding to the metrics, applies the metrics to a candidate document and obtains respective returned values, applies the weights to the returned values and Sums the results to obtain a Document Dissimilarity (DD) value. This DD is compared with a Dissimilarity Threshold (DT) and the candidate document is stored if the DD is less than the DT. A user can apply relevance values to the Search results and the agent modifies the weights accordingly. The agent can be used to improve a language model for use in Speech recognition applications and the like

Evolution of the snow height in the Alps over the 20th century using the regional atmospheric model MAR

peer reviewedL’évolution de l’enneigement dans les Alpes peut fortement affecter le tourisme, mais aussi la disponibilité en eau de la région. Dans cette étude, nous avons reproduit l’évolution du climat des Alpes au cours du 20e siècle à l’aide du modèle atmosphérique régional MAR forcé par trois réanalyses (ERA-20C, NCEP/NCAR et ERA-Interim). Le MAR montre que la hauteur de neige a augmenté depuis le début du 20e siècle, d’abord uniquement en haute altitude, puis également aux altitudes inférieures, avant de connaitre une forte et brusque diminution entre 1985 et 1990. Cette évolution, qui est en accord avec les observations décrites dans la littérature, est directement liée aux fluctuations de la NAO et de l’AO. En effet, les changements de circulation atmosphérique que traduisent la NAO et l’AO entrainent des variations de température et de précipitations qui déterminent directement la hauteur de neige dans les Alpes.The evolution of the snow height over the Alps can strongly impact tourism, but also the water availability of the region. In this study, we have reproduced the evolution of the climate in the Alps over the 20th century with the help of the regional atmospheric model MAR forced by three reanalyses (ERA-20C, NCEP/NCAR, and ERA-Interim). MAR shows that the snow height has increased since the beginning of the 20th century, first only at higher altitudes, then also at lower levels, before knowing a strong and abrupt decrease between 1985 and 1990. This evolution, which is consistent with observations given in the literature, is directly linked with the trends of NAO and AO. In fact, the atmospheric circulation changes highlighted by NAO and AO induce temperature and precipitation changes that directly determine the snow height in the Alps

The MAR model performances over Belgium

This presentation deals with the set-up of the regional climate model MAR over Belgium. It also presents the performances of MAR to simulate the present-day climate following three reanalysis used as forcing of the model (ERA-Interim, ERA-20C and NCEP/NCAR-v1)

Evaluation of model “Modèle Atmosphérique Régional” (MAR) capacity to simulate rainfall season in Intertropical Africa

peer reviewedEn Afrique intertropicale, le climat est essentiellement caractérisé par les quantités de précipitations et leur régime annuel. Ces précipitations et leur évolution au cours de la période 1970-1999 ont été modélisées à l’aide du Modèle Atmosphérique Régional (MAR), développé à l’ULg, en le forçant par les réanalyses NCEP1 ainsi que par les sorties de trois modèles globaux (GCM) de la base de données CMIP5. Ces simulations ont ensuite été comparées aux observations maillées du Climate Research Unit (CRU). Il ressort de nos investigations que la simulation du modèle MAR forcé par les réanalyses NCEP1 parvient à mieux reproduire les lames d’eau et leur régime annuel dans les régions semi-arides qu'en régions équatoriales. En revanche, les simulations du MAR forcé par les sorties des GCM sont peu voire très peu satisfaisantes sur l'ensemble du domaine intertropical tant au niveau des quantités que de la saisonnalité des précipitations.In Intertropical Africa, climate is essentially characterized by the amount of precipitation and its annual regime. These precipitations and their evolution during the period 1970-1999 are simulated thanks to the Regional Atmospheric Model (MAR), developed at the ULg, and forced by the NCEP1 reanalyses and by the outputs of three global models (GCM) of the CMIP5 database. These MAR simulations are compared to the gridded data of the Climate Research Unit (CRU). It is clear from our investigations that the simulation of the MAR model forced by the NCEP1 reanalyses is better reproducing the quantities as well as the annual rainfall regime in the semi-arid regions than in equatorial regions. On the other hand, simulations of the MAR forced by the outputs of the GCMs are globally unsatisfactory throughout the intertropical domain in terms of quantities as well as the seasonality of precipitation.AFRIFOR