in Cryosphere (2019), 13
In the context of global warming, growing attention is paid to the evolution of the Greenland ice sheet (GrIS) and its contribution to sea-level rise at the centennial timescale. Atmosphere–GrIS interactions, such as the temperature–elevation and the albedo feedbacks, have the potential to modify the surface energy balance and thus to impact the GrIS surface mass balance (SMB). In turn, changes in the geometrical features of the ice sheet may alter both the climate and the ice dynamics governing the ice sheet evolution. However, changes in ice sheet geometry are generally not explicitly accounted for when simulating atmospheric changes over the Greenland ice sheet in the future. To account for ice sheet–climate interactions, we developed the first two-way synchronously coupled model between a regional atmospheric model (MAR) and a 3-D ice sheet model (GRISLI). Using this novel model, we simulate the ice sheet evolution from 2000 to 2150 under a prolonged representative concentration pathway scenario, RCP8.5. Changes in surface elevation and ice sheet extent simulated by GRISLI have a direct impact on the climate simulated by MAR. They are fed to MAR from 2020 onwards, i.e. when changes in SMB produce significant topography changes in GRISLI. We further assess the importance of the atmosphere–ice sheet feedbacks through the comparison of the two-way coupled experiment with two other simulations based on simpler coupling strategies: (i) a one-way coupling with no consideration of any change in ice sheet geometry; (ii) an alternative one-way coupling in which the elevation change feedbacks are parameterized in the ice sheet model (from 2020 onwards) without taking into account the changes in ice sheet topography in the atmospheric model. The two-way coupled experiment simulates an important increase in surface melt below 2000 m of elevation, resulting in an important SMB reduction in 2150 and a shift of the equilibrium line towards elevations as high as 2500 m, despite a slight increase in SMB over the central plateau due to enhanced snowfall. In relation with these SMB changes, modifications of ice sheet geometry favour ice flux convergence towards the margins, with an increase in ice velocities in the GrIS interior due to increased surface slopes and a decrease in ice velocities at the margins due to decreasing ice thickness. This convergence counteracts the SMB signal in these areas. In the two-way coupling, the SMB is also influenced by changes in fine-scale atmospheric dynamical processes, such as the increase in katabatic winds from central to marginal regions induced by increased surface slopes. Altogether, the GrIS contribution to sea-level rise, inferred from variations in ice volume above floatation, is equal to 20.4 cm in 2150. The comparison between the coupled and the two uncoupled experiments suggests that the effect of the different feedbacks is amplified over time with the most important feedbacks being the SMB–elevation feedbacks. As a result, the experiment with parameterized SMB–elevation feedback provides a sea-level contribution from GrIS in 2150 only 2.5 % lower than the two-way coupled experiment, while the experiment with no feedback is 9.3 % lower. The change in the ablation area in the two-way coupled experiment is much larger than those provided by the two simplest methods, with an underestimation of 11.7 % (14 %) with parameterized feedbacks (no feedback). In addition, we quantify that computing the GrIS contribution to sea-level rise from SMB changes only over a fixed ice sheet mask leads to an overestimation of ice loss of at least 6 % compared to the use of a time variable ice sheet mask. Finally, our results suggest that ice-loss estimations diverge when using the different coupling strategies, with differences from the two-way method becoming significant at the end of the 21st century. In particular, even if averaged over the whole GrIS the climatic and ice sheet fields are relatively similar; at the local and regional scale there are important differences, highlighting the importance of correctly representing the interactions when interested in basin scale changes.
in Atmosphere (2019), 10(1), 34
The aim of this study is to assess the sensitivity of convective precipitation modelled by the regional climate model MAR (Modèle Atmosphérique Régional) over 1987–2017 to four newly implemented convective schemes: the Bechtold scheme coming from the MESO-NH regional model and the Betts-Miller-Janjić, Kain-Fritsch and modified Tiedtke schemes coming from the WRF regional model. MAR version 3.9 is used here at a resolution of 10 km over a domain covering Belgium using the ERA-Interim reanalysis as forcing. The simulated precipitation is compared against SYNOP and E-OBS gridded precipitation data. Trends in total and convective precipitation over 1987–2017 are discussed. None of the MAR experiments compares better with observations than the others and they all show the same trends in (extreme) precipitation. Over the period 1987–2017, MAR suggests a significant increase in the mean annual precipitation amount over the North Sea but a significant decrease over High Belgium.
in Cryosphere (2018), 12
Estimates for the recent period and projections of the Antarctic surface mass balance (SMB) often rely on high-resolution polar-oriented regional climate models (RCMs). However, RCMs require large-scale boundary forcing fields prescribed by reanalyses or general circulation models (GCMs). Since the recent variability of sea surface conditions (SSCs, namely sea ice concentration, SIC, and sea surface temperature, SST) over the Southern Ocean is not reproduced by most GCMs from the 5th phase of the Coupled Model Intercomparison Project (CMIP5), RCMs are then subject to potential biases. We investigate here the direct sensitivity of the Antarctic SMB to SSC perturbations around the Antarctic. With the RCM “Modèle Atmosphérique Régional” (MAR), different sensitivity experiments are performed over 1979–2015 by modifying the ERA-Interim SSCs with (i) homogeneous perturbations and (ii) mean anomalies estimated from all CMIP5 models and two extreme ones, while atmospheric lateral boundary conditions remained unchanged. Results show increased (decreased) precipitation due to perturbations inducing warmer, i.e. higher SST and lower SIC (colder, i.e. lower SST and higher SIC), SSCs than ERA-Interim, significantly affecting the SMB of coastal areas, as precipitation is mainly related to cyclones that do not penetrate far into the continent. At the continental scale, significant SMB anomalies (i.e greater than the interannual variability) are found for the largest combined SST/SIC perturbations. This is notably due to moisture anomalies above the ocean, reaching sufficiently high atmospheric levels to influence accumulation rates further inland. Sensitivity experiments with warmer SSCs based on the CMIP5 biases reveal integrated SMB anomalies (+5 % to +13 %) over the present climate (1979–2015) in the lower range of the SMB increase projected for the end of the 21st century.
Doctoral thesis (2018)
In Belgium, the future response of the climate to increasing greenhouse gas concentration is not clear, especially with regard to the perturbations of the precipitation regime, snow cover, and global radiation. On the one hand, existing studies show results which differ strongly either according to the future scenario, or from one model to another. On the other hand, there is even an absence of studies focussing on Belgium regarding future changes in snow cover and global radiation. Given their potential impacts on the society (water management, energy supply, biodiversity, tourism), future changes in precipitation, snow cover, and global radiation require further research. As the orography, the exposition to the dominant winds, and the proximity of the North Sea determine a large spatial variability in the Belgian climate, the latter requires a fine representation of these features to be properly simulated. Compared to global climate models (GCM), regional climate models (RCM) are recognized for their ability to represent climatic phenomena with higher spatial resolutions. In the framework of this doctoral thesis, the RCM MAR (for "Modèle Atmosphérique Régional" in French), which is developed at the Laboratory of Climatology and Topoclimatology of the University of Liège, was applied for the first time to Belgium. The aim was first to assess the performances of MAR over Belgium and then to study the current and future evolution of hydroclimatic conditions favouring floods, and also the current and future evolution of global radiation. For this purpose, historical simulations were performed over 1959-2014. Future projections (2006-2100) were then performed under the most pessimist IPCC future scenario (RCP8.5). The horizontal resolution used for both historical and future simulations is 5 km. By comparing the MAR outputs to ground-based measurements from 20 weather stations over 2008-2014, the results show that MAR successfully simulates the spatial and temporal variability of the Belgian climate. In fact, the biases found in the MAR results are non-significant and the correlation coefficients are satisfying with regard to temperature, precipitation, snow height, global radiation and cloudiness. The MAR results are particularly satisfying during the winter months and in High Belgium where the climate is the coldest. Regarding hydroclimatic conditions favouring floods, we focused on the Ourthe catchment. In this river, about 70 % of floods occur during the winter months and result from either the rapid melting of the snow pack covering the Ardennes eventually combined with rainfall or abundant rainfall alone. The current evolution of hydroclimatic conditions favouring floods was first assessed for the period 1959-2010. Conditions favouring floods in the Ourthe River present a negative trend over 1959–2010 as a result of a decrease in snow accumulation and a shortening of the snow season. Regarding the impact of the evolution of extreme precipitation events on hydroclimatic conditions favouring floods, the signal is less clear because the trends depend on the data used to force the MAR model. By the end of the 21st century, under the most pessimist scenario, the results show an acceleration of the snow cover depletion resulting in a decrease in conditions favouring floods. Further, the impact of the evolution of extreme precipitation events on hydroclimatic conditions favouring floods, no significant change was found although these trends are subject to uncertainties due to the deficiencies of the convective scheme of MAR. Regarding global radiation, its current evolution was first assessed for the period 1959-2010. In addition, we consider two distinct periods in our analysis: 1959-1979 (dimming) and 1980-2010 (brightening). For both the dimming and the brightening periods, our results show that the annual global radiation trends are mainly driven by global radiation changes in spring and summer. The increase in global radiation observed in Belgium since the 1980s and especially since the 2000s could mainly be explained by a decrease in low and medium cloud cover. This would strengthen the effect of the decrease in aerosol load on global radiation that has been observed in Europe since the 1980s. The origin of these changes in cloudiness is not clear and could result from changes in both aerosol-cloud interactions and atmospheric-circulation, such as more frequent tropical air advections and more frequent anticyclonic conditions over Western Europe due to the poleward shift of extratropical storm tracks. These changes in the atmospheric circulation may result from global warming and may persist in the future. In fact, by the end of the 21st century, under the most pessimist scenario, the models simulate an increase in the blocking regime frequency in summer over Europe. For Belgium, this implies more frequent anticyclonic conditions favouring cloudless conditions. The future projections performed with MAR exhibit significant decreasing total cloud cover, and particularly decreasing low and medium cloud cover. However, this declining cloud cover leads to contrasting changes in global radiation depending on the data used to force MAR.
Article for general public (2018)
Entre 1960 et 1980, le rayonnement solaire reçu à la surface de la Terre a diminué. A l'inverse, depuis 1980, une augmentation est observée en Europe et en Amérique du Nord. Comment expliquer ces variaitons?
Article for general public (2018)
Article for general public (2018)
Le climat en Europe d'ici 2100 si aucune mesure d'adaptation ou d'atténuation du réchauffement climatique n'est prise d'ici la fin du siècle. Chiffres issus de publications scientifiques.
in Climate Services (2018), 11
The CORDEX.be project created the foundations for Belgian climate services by producing high-resolution Belgian climate information that (a) incorporates the expertise of the different Belgian climate modeling groups and that (b) is consistent with the outcomes of the international CORDEX (“COordinated Regional Climate Downscaling Experiment”) project. The key practical tasks for the project were the coordination of activities among different Belgian climate groups, fostering the links to specific international initiatives and the creation of a stakeholder dialogue. Scientifically, the CORDEX.be project contributed to the EURO-CORDEX project, created a small ensemble of High-Resolution (H-Res) future projections over Belgium at convection-permitting resolutions and coupled these to seven Local Impact Models. Several impact studies have been carried out. The project also addressed some aspects of climate change uncertainties. The interactions and feedback from the stakeholder dialogue led to different practical applications at the Belgian national level
in Atmosphere (2018), 9(7), 262
The use of regional climate models (RCMs) can partly reduce the biases in global radiative flux (Eg↓) that are found in reanalysis products and global models, as they allow for a finer spatial resolution and a finer parametrisation of surface and atmospheric processes. In this study, we assess the ability of the MAR («Modèle Atmosphérique Régional») RCM to reproduce observed changes in Eg↓, and we investigate the added value of MAR with respect to reanalyses. Simulations were performed at a horizontal resolution of 5 km for the period 1959–2010 by forcing MAR with different reanalysis products: ERA40/ERA-interim, NCEP/NCAR-v1, ERA-20C, and 20CRV2C. Measurements of Eg↓ from the Global Energy Balance Archive (GEBA) and from the Royal Meteorological Institute of Belgium (RMIB), as well as cloud cover observations from Belgocontrol and RMIB, were used for the evaluation of the MAR model and the forcing reanalyses. Results show that MAR enables largely reducing the mean biases that are present in the reanalyses. The trend analysis shows that only MAR forced by ERA40/ERA-interim shows historical trends, which is probably because ERA40/ERA-interim has a better horizontal resolution and assimilates more observations than the other reanalyses that are used in this study. The results suggest that the solar brightening observed since the 1980s in Belgium has mainly been due to decreasing cloud cover.
Poster (2018, April 13)
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.
The main objectives of the CORDEX.be project were: 1. Contribute to the international climate community by participating to EURO-CORDEX by performing regional climate simulations over Europe. 2. Provide an ensemble of High-Resolution (H-Res) climate simulations over Belgium i.e. to create a small ensemble of high-resolution future projections over Belgium at convectionpermitting resolutions. 3. Couple these model simulations to seven local-impact models for impact studies. 4. Present an overview of the ongoing climate modeling activities in Belgium. 5. Provide coherent climate information for Belgium targeted to end-users, backed by: (i) a unified framework for the H-Res climate runs and (ii) uncertainty estimations on the climate change signal; 6. Provide and present a climate-impact report for stakeholders and the general public that highlight the most important results of the project.
Conference (2017, November 17)
In the framework of the CORDEX.be project funded by Belspo, most universities and research institutes of Belgium have worked together in order to gather existing and ongoing Belgian research activities in the domain of climate modelling to create a coherent scientific basis for future climate services in Belgium. The Laboratory of Climatology of the University of Liège has performed climate simulations using the regional climate model MAR (“Modèle Atmosphérique Régional” in French) at a resolution of 5 km over the period 1959-2014. This research aims to study the evolution of several variables computed by MAR during the winters of the last 50 years. Except in snow accumulation, results show no statistically significant trend in winter temperature or precipitation in Belgium. This results from the strong influence of natural large-scale/low-frequency oscillations in the atmospheric circulation in winter such as the North Atlantic Oscillation.
Scientific conference (2017, September 14)
This research discusses the results obtained by running the MAR model over the CORDEX.be and EURO-CORDEX domains. The MAR results depend on its horizontal resolution (5 - 10 - 20 km), its version (v3.6 vs v3.7), and on the reanalysis used as forcing.
Poster (2017, September 04)
Many studies show that the surface solar radiation has underwent large variations over the second half of the 20th century as a result of variations in cloud cover and aerosol loading in the atmosphere. However, it is difficult to build strong conclusions before the 1950s because of the observations scarcity. The evolution of the surface solar radiation has been reconstructed over 1900-2014 using the regional model MAR (« Modèle Atmosphérique Régional ») which has recently been chosen to be part of the EURO-CORDEX project, thanks to the CORDEX.be project. Simulations were performed at a horizontal resolution of 5 km over a domain of 600 x 550 km² covering Belgium. Boundary conditions were provided by four reanalysis products: ERA-interim (1979-2014) completed by the ERA40 (1958-1978), NCEP/NCAR-v1 (1948-2014), ERA-20C (1900-2010) and 20CRV2C (1900-2010). Surface solar radiation measurements from the Global Energy Balance Archive and cloud cover observations from Belgocontrol covering 1966-2007 were used for the evaluation of the MAR model and the forcing reanalyses. Results show that MAR produces much better results than the reanalyses. The driving reanalyses can generate divergent trends while they assimilate observations and are supposed to represent the same climate.
in Bulletin de la Société Géographique de Liège (2017), 68
On December 2010, several snow events allowed an exceptional snow cover over Belgium. 27 days with snow cover were observed at Uccle and snow depths of 20, 30 and 70 cm were measured on Christmas 2010 respectively at Uccle, Bierset and Mont Rigi in the Hautes-Fagnes. On December 20, while the entire Belgium was covered by a thick blanket of snow, warmer air invaded the country on December 21. This air was quickly replaced by polar air in Lower and Central Belgium (including Bierset). Heavy snowfalls were observed on December 22 and 23, except in the Upper Ardennes where rainfalls occurred under positive temperature which then dropped to -5°C. This event was due to a strong thermal inversion in the lower layers with warm air at 850 hPa above the Ardennes only. This paper aims to explain this atypical extreme event using the regional climate model MAR developed at the University of Liège
in Dahech, Salem; Charfi, Sami (Eds.) Actes du XXXe colloque de l'Association Internationale de Climatologie : Climat, ville et environnement (2017, July)
Many studies show that the surface solar radiation has underwent large variations over the second half of the 20th century as a result of variations in cloud cover and aerosol loading in the atmosphere. However, it is difficult to build strong conclusions before the 1950' because of the observations scarcity. The evolution of the surface solar radiation has been reconstructed over 1900-2014 using the regional model MAR (« Modèle Atmosphérique Régional ») in Belgium. Boundary conditions were provided by four reanalysis products : the ERA-interim (1979-2014) completed by the ERA40 (1958-1978), the NCEP/NCAR-v1 (1948-2014), the ERA-20C (1900-2010) and the 20CRV2C (1900-2010). Results show that the reanalyses can generate divergent trends while they assimilate observations and are supposed to represent the same climate.
in Dahech, Salem; Charfi, Sami (Eds.) Actes du XXXème colloque de l'Association Internationale de Climatologie - Climat, ville et environnement (2017, July)
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.
in Dahech, Salem; Charfi, Sami (Eds.) Actes du XXXe colloque de l'Association Internationale de Climatologie : CLIMAT, VILLE ET ENVIRONNEMENT (2017, July)
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.
in International Journal of Climatology (2017), 37(5), 27822796
The Ourthe River, in the south-east of Belgium, has a catchment area of 3,500 km2 and is one of the main tributaries of the Meuse River. In the Ourthe, most of the flood events occur during winter and about 50% of them are due to heavy rainfall events combined to an abrupt melting of the snowpack covering the Ardennes massif during winter. This study aims to determine whether trends in extreme hydroclimatic events generating floods can be detected over the last century in Belgium, where a global warming signal can be observed. Hydroclimatic conditions favourable to floods were reconstructed over 1959- 2010 using the regional climate model MAR (“Modèle Atmosphérique Régional”) forced by the ERA-Interim/ERA-40, the ERA-20C and the NCEP/NCAR-v1 reanalyses. Extreme run-off events, which could potentially generate floods, were detected using run-off caused by precipitation events and snowpack melting from the MAR model. In the validation process, the MAR-driven temperature, precipitation and snow depth were successfully compared to daily weather data over the period 2008-2014 for 20 stations in Belgium. MAR also showed its ability to detect up to 90% of the hydroclimatic conditions which effectively generated observed floods in the Ourthe River over the period 1974- 2010. Conditions favourable to floods in the Ourthe River catchment present a negative trend over the period 1959-2010 as a result of a decrease in snow accumulation and a shortening of the snow season. This trend is expected to accelerate in a warmer climate. However, regarding the impact of the extreme precipitation events evolution on conditions favouring floods, the signal is less clear since the trends depend on the reanalysis used to force the MAR model.
Article for general public (2017)
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.
Article for general public (2017)
Book published by FEGEPRO (Fédération des professeurs de géographie) (2017)
Dans une première partie de l’ouvrage, les auteurs traitent de l’état de la question des variations climatiques, en s’attachant aux explications naturelles et anthropiques des variations passées, tout en s’attardant sur les variations du Pléistocène à aujourd’hui. La question des variations attendues pour le futur retient l’attention, présentée sous la forme de différents scénarios, avec un focus porté sur l’Europe. Dans une seconde partie de l’ouvrage, sont abordées les conséquences et impacts spatiaux des variations climatiques. Si la fonte des banquises ainsi que la hausse du niveau des mers ainsi que leur acidification ont retenu l’attention des auteurs, ils s’attardent également sur la multiplication des événements climatiques extrêmes, les changements des écosystèmes, les problématiques des déplacés climatiques et des impacts sanitaires, tout en pointant ce qui reste en débat. La troisième partie consacrée aux politiques et aux actions ne manquera pas de susciter notre curiosité, tant au niveau des solutions techniques, que des modes de production ou de consommation, tout en réaffirmant que les choix politiques posés en matière d’aménagement de territoire et d’urbanisme s’avèrent déterminants pour infléchir sur les comportements individuels.
Article for general public (2016)
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.
Poster (2016, August 29)
This research aims to assess the ability of the regional climate model MAR ("Modèle Atmosphérique Régional") to reconstruct the observed twentieth century climatology of extreme events and solar radiation in Belgium, as a necessary condition for reliable future projections. Simulations were performed by forcing MAR with several reanalyses: the ERA40/ERA-Interim, the ERA-20C and the NCEP/NCAR-v1. The results suggests that increasing air temperature would have generated decreasing relative humidity which would have lead to a decrease in cloudiness and an increase in solar downward radiation. This research illustrates the dependency between RCMs and their forcings. The forcing reanalyses can generate divergent trends while contrary to Global Climate Models (GCM), the reanalyses assimilate observations and are supposed to represent the same climate.
Conference (2016, June 08)
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).
Conference (2016, April 19)
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.
Conference (2015, November 13)
The Ourthe River (southeast of Belgium) is one of the main tributaries of the Meuse River with a catchment area of 3500 km². About 50 % of the floods which occur in the Ourthe River catchment are due to rainfall events associated with the melting of the snow which covers the Ardennes in winter. In this study, hydroclimatic conditions favourable to flooding were reconstructed over the period 1958-2014 using the regional climate model MAR (« Modèle Atmosphérique Régional ») forced by the ERA-interim reanalysis and by the NCEP1 reanalysis. As validation, the MAR results were compared to weather station-based data. A trends analysis was then performed in order to study the evolution of conditions favourable to flooding in the Ourthe River catchment. When the MAR model is forced by the NCEP1 reanalysis, results show a significant decrease in hydroclimatic conditions favourable to flooding because of a decrease in snow accumulation as well as a decrease in the frequency of extreme precipitation events in winter. When MAR is forced by the ERA-interim reanalysis, non-significant trends are found, which could be explained by an underestimation of the precipitation amount computed by the ERA-40 reanalysis before 1979. Further studies are needed to explain the decreasing trends in snow accumulation and extreme precipitation events. Moreover, an hydrological model could also be forced by the MAR outputs in order to improve flood detection.
in Erpicum, Michel (Ed.) Actes du XXVIIIe colloque annuel de l’Association Internationale de Climatologie : Modélisations et variabilités (2015, July)
The “Modèle Atmosphérique Régionale” MAR is a regional climate model originally developed to study the polar ice sheets. In this study, the MAR model has been adapted to Belgium in order to study the snow cover evolution of the High Fens (east of Belgium), a region covered by snow on average one to two months per year. As validation, we have sucessfully compared MAR based daily snow heights with snowcam-based and/or laser sensor-based observations over the period 2008-2013. Then, the model has been forced by ERA-Interim since 1958 to study the snow cover evolution during the last fifty years at the summit of Belgium. The results show no significant trend despite global warming.
Conference (2015, April 16)
The MAR model is a regional climate model originally developped for the polar regions to study the surface mass balance. In this study, the MAR model has been adapted to Belgium in order to study the snow cover evolution of the Hautes Fagnes (south-east of Belgium), a region covered by snow one to two months per year. As validation, we have sucessfully compared MAR based daily snow heights with snowcam-based observations. Then, the model has been forced by ERA-Interim since 1958 to study the snow cover evolution during the last fifty years at the summit of Belgium. The results show non-significant trend.
Poster (2015, April 14)
During the two last decades, the Greenland ice sheet (GrIS) contribution to the global mean sea level rise has significantly increased. But, difficulties remain to assess GrIS future contribution because of large uncertainties linked to the feedback between the surface mass balance (SMB) and GrIS topography changes. The regional climate MAR model has been coupled with the GRISLI ice sheet model, in order to account of this feedback in the future projections. The aim of this study is to assess the pertinence of the MAR-GRISLI coupling which requires long computation time. In order to identify GRISLI sensitivity to MAR forcing, GRISLI has been forced with various non-coupled (i.e. using a fixed topography), coupled and modified non-coupled MAR outputs. To adapt the non-coupled MAR outputs to the GRISLI topography changes, we use an interpolation technique based on SMB vs elevation vertical gradient. These experiences evaluate the performances/limits of this interpolation technique used to avoid a RCM-ice sheet model coupling.
Master's dissertation (2014)
During the two last decades, the Greenland ice sheet (GrIs) contribution to the global mean sea level (GMSL) rise has significantly increased. In the future, difficulties remain to assess the GrIs contribution to GMSL rise because of large uncertainties linked to the feedback between the surface mass balance (SMB) and the elevation of the GrIs. In 2013, Xavier Fettweis, my promoter, has coupled a regional climate model (RCM), the model MAR, with an ice sheet model (ISM), the model GRISLI, in order to account of this feedback and, in this way, to improve the assessment of the future GrIs contribution to the GMSL rise. The aim of this study is to assess the pertinence of the MAR−GRISLI coupling which requires long computation time. Nine imulations were carried out with GRISLI. Six of these simulations consisted in forcing GRISLI with several present days MAR outputs (SMB and surface temperature) in order to identify the GRISLI biases. The three last simulations consisted in forcing GRISLI until 2100 with future non-coupled, coupled and modified non- coupled MAR outputs in order to find a technique to avoid the coupling. The results show that initial conditions need to be improved and that the ice flow velocities required recalibration because an abnormal present-day thickening of the GrIs margins. Ice calving only depends on ice sheet extension because of constant ice flow velocities. The MAR−GRISLI coupling can be avoided until the middle of the 2080s. Beyond these years, the SMB correction is too large so that the thinning of the GrIs margins is overestimated. In a further study, the SMB correction could be reduced to avoid the MAR−GRISLI coupling over longer periods. GRISLI could be improved or replaced by a more complex ISM with dynamic ice flow velocities to enhance the results.