Inondations de l'Aude du 15 octobre 2018 : analyse météorologique, conséquences hydrologiques et prévisibilité

2020 ◽  
pp. 046
Author(s):  
Michaël Kreitz ◽  
Christophe Calas ◽  
Sébastien Baille
Keyword(s):  
Weather Prediction ◽  
Heavy Precipitation ◽  
Great Variability ◽  
Precipitation Event ◽  
Limited Area ◽  
Synoptic Scale ◽  
Heavy Precipitation Event ◽  
River Catchment ◽  
Convergence Line ◽  
Low Level Jet

Dans la nuit du 14 au 15 octobre 2018, un épisode méditerranéen se déclenche sur le département de l'Aude, déversant jusqu'à 300 mm en un peu moins de 10 heures dans la région de Carcassonne, générant des crues meurtrières sur le bassin moyen de l'Aude et de ses affluents. Les ingrédients météorologiques typiques d'un tel événement sont bien présents : entrée droite d'un jet de sud en altitude, jet de basses couches méditerranéen chaud et humide alimentant une ligne de convergence. Le paroxysme de l'épisode s'étant produit à l'est immédiat de Carcassonne, région habituellement située à la périphérie des épisodes les plus intenses, les durées de retour des précipitations sur 6 heures sont au final d'ordre centennal. Même si la prévisibilité d'un épisode méditerranéen est relativement bonne à grande échelle, les modèles déterministes et leurs ensembles, qu'ils soient globaux ou à aire limitée, montrent une grande variabilité d'un réseau à l'autre, rendant très difficile la localisation précise du paroxysme pluvieux. During the night of 14th October 2018 a Mediterranean Heavy Precipitation Event occurred over the Aude département in Southern France, bringing up to 300 mm of rain in about 10 hours over the Carcassonne area, and generating deadly floods in the Aude River catchment. Typical meteorological ingredients were involved: an upper-jet right-entrance region, and a warm and wet low-level jet feeding a convergence line. As the peak of the event occurs around Carcassonne which is less familiar to such events, the return period for 6-hour rainfall was close to one-hundred years. The predictability of such events is rather good on a synoptic scale. However, when it comes to precise localisation and intensities, numerical weather prediction (NWP) models (be they deterministic or ensembles, global or limited-area ones) show a great variability between consecutive runs, making the exercise very challenging for forecasters.

scholarly journals Assimilating X- and S-Band Radar Data for a Heavy Precipitation Event in Italy

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1727
Author(s):  
Valerio Capecchi ◽  
Andrea Antonini ◽  
Riccardo Benedetti ◽  
Luca Fibbi ◽  
Samantha Melani ◽  
...  
Keyword(s):  
Extreme Event ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Flash Floods ◽  
Precipitation Event ◽  
Weather Research And Forecasting ◽  
Limited Area ◽  
Heavy Precipitation Event ◽  
The Town

During the night between 9 and 10 September 2017, multiple flash floods associated with a heavy-precipitation event affected the town of Livorno, located in Tuscany, Italy. Accumulated precipitation exceeding 200 mm in two hours was recorded. This rainfall intensity is associated with a return period of higher than 200 years. As a consequence, all the largest streams of the Livorno municipality flooded several areas of the town. We used the limited-area weather research and forecasting (WRF) model, in a convection-permitting setup, to reconstruct the extreme event leading to the flash floods. We evaluated possible forecasting improvements emerging from the assimilation of local ground stations and X- and S-band radar data into the WRF, using the configuration operational at the meteorological center of Tuscany region (LaMMA) at the time of the event. Simulations were verified against weather station observations, through an innovative method aimed at disentangling the positioning and intensity errors of precipitation forecasts. A more accurate description of the low-level flows and a better assessment of the atmospheric water vapor field showed how the assimilation of radar data can improve quantitative precipitation forecasts.

scholarly journals Assimilating X- and S-band Radar Data for a Heavy Precipitation Event in Italy

2021 ◽  
Author(s):  
Valerio Capecchi ◽  
Andrea Antonini ◽  
Riccardo Benedetti ◽  
Luca Fibbi ◽  
Samantha Melani ◽  
...  
Keyword(s):  
Extreme Event ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Flash Floods ◽  
Precipitation Event ◽  
Weather Research And Forecasting ◽  
Limited Area ◽  
Heavy Precipitation Event ◽  
The Town

During the night between 9 and 10 September 2017, multiple flash floods associated to a heavy-precipitation event affected the town of Livorno, located in Tuscany, Italy. Accumulated precipitation exceeding 200 mm in two hours, associated with a return period higher than 200 years, caused all the largest streams of the Livorno municipality to flood several areas of the town. We used the limited-area Weather Research and Forecasting (WRF) model, in a convection-permitting setup, to reconstruct the extreme event leading to the flash floods. We evaluated possible forecasting improvements emerging from the assimilation of local ground stations and X- and S-band radar data into the WRF, using the configuration operational at the meteorological center of Tuscany region (LaMMA) at the time of the event. Simulations were verified against weather station observations, through an innovative method aimed at disentangling the positioning and intensity errors of precipitation forecasts. By providing more accurate descriptions of the low-level flow and a better assessment of the atmospheric water vapour, the results demonstrate that assimilating radar data improved the quantitative precipitation forecasts.

scholarly journals The heavy precipitation event of 14–15 October 2018 in the Aude catchment: a meteorological study based on operational numerical weather prediction systems and standard and personal observations

2021 ◽  
Vol 21 (3) ◽  
pp. 1135-1157
Author(s):  
Olivier Caumont ◽  
Marc Mandement ◽  
François Bouttier ◽  
Judith Eeckman ◽  
Cindy Lebeaupin Brossier ◽  
...  
Keyword(s):  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Precipitation Event ◽  
Synoptic Situation ◽  
Heavy Precipitation Event ◽  
Cold Air ◽  
Numerical Weather ◽  
Prediction Systems

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case features typical characteristics of Mediterranean heavy precipitation events such as its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, as well as some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground. Mediterranean Sea surface temperature and soil moisture anomalies are briefly reviewed, as they are known to play a role in this type of hydrometeorological events. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest, and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

scholarly journals The heavy precipitation event of 14–15 October 2018 in the Aude catchment: A meteorological study based on operational numerical weather prediction systems and standard and personal observations

2020 ◽  
Author(s):  
Olivier Caumont ◽  
Marc Mandement ◽  
François Bouttier ◽  
Judith Eeckman ◽  
Cindy Lebeaupin Brossier ◽  
...  
Keyword(s):  
Numerical Weather Prediction ◽  
Weather Prediction ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Precipitation Event ◽  
Synoptic Situation ◽  
Heavy Precipitation Event ◽  
Cold Air ◽  
Numerical Weather ◽  
Prediction Systems

Abstract. The case of the heavy precipitation event on 14 and 15 October 2018 which has led to severe flash flooding in the Aude watershed in south-western France is studied from a meteorological point of view using deterministic and probabilistic numerical weather prediction systems, as well as a unique combination of observations from both standard and personal weather stations. This case is typical of Mediterranean heavy precipitation events due to its classic synoptic situation and its quasi-stationary convective precipitation that regenerates continuously, but with some peculiarities such as the presence of a former hurricane and a pre-existing cold air mass close to the ground. It is shown that the positive Mediterranean sea surface temperature anomaly may have played an aggravating role in the amount of precipitation that poured into the Aude basin. On the other hand, soil moisture does not seem to have played a significant role. A study of rainfall forecasts shows that the event had limited predictability, in particular given the small size of the watersheds involved. It is shown that the stationarity of precipitation, whose estimation benefits from data from personal stations, is linked to the presence near the ground of a trough and a strong potential virtual temperature gradient, the stationarity of both of which is highlighted by a combination of observations from standard and personal stations. The forecast that comes closest to the rainfall observations contains the warmest, wettest and fastest low-level jet and also simulates near the ground a trough and a marked boundary between cold air in the west and warm air in the east, both of which are stationary.

scholarly journals Characterization of the air–sea exchange mechanisms during a Mediterranean heavy precipitation event using realistic sea state modelling

2020 ◽  
Vol 20 (3) ◽  
pp. 1675-1699 ◽  
Author(s):  
César Sauvage ◽  
Cindy Lebeaupin Brossier ◽  
Marie-Noëlle Bouin ◽  
Véronique Ducrocq
Keyword(s):  
Weather Prediction ◽  
Heavy Precipitation ◽  
Precipitation Event ◽  
Turbulent Heat ◽  
Coupled Modes ◽  
Sea State ◽  
Heavy Precipitation Event ◽  
Easterly Wind ◽  
Low Level ◽  
The Waves

Abstract. This study investigates the mechanisms acting at the air–sea interface during a heavy precipitation event that occurred between 12 and 14 October 2016 over the north-western Mediterranean area and led to large amounts of rainfall (up to 300 mm in 24 h) over the Hérault region (southern France). The study case was characterized by a very strong (>20 m s−1) easterly to south-easterly wind at low level that generated very rough seas (significant wave height of up to 6 m) along the French Riviera and the Gulf of Lion. In order to investigate the role of the waves on air–sea exchanges during such extreme events, a set of numerical experiments was designed using the Météo-France kilometre-scale AROME-France numerical weather prediction model – including the WASP (Wave-Age-dependant Stress Parametrization) sea surface turbulent flux parametrization – and the WaveWatch III wave model. Results from these sensitivity experiments in the forced or coupled modes showed that taking the waves generated by the model into account increases the surface roughness. Thus, the increase in the momentum flux induces a slowdown of the easterly low-level atmospheric flow and a displacement of the convergence line at sea. Despite strong winds and a young sea below the easterly flow, the turbulent heat fluxes upstream of the precipitating system are not significantly modified. The forecast of the heaviest precipitation is finally modified when the sea state is taken into account; notably, in terms of location, this modification is slightly larger in the forced mode than in the coupled mode, as the coupling interactively balances the wind sea, the stress and the wind.

scholarly journals Characterization of the air-sea exchanges mechanisms during a Mediterranean heavy precipitation event using realistic sea state modelling

2019 ◽  
Author(s):  
César Sauvage ◽  
Cindy Lebeaupin Brossier ◽  
Marie-Noëlle Bouin ◽  
Véronique Ducrocq
Keyword(s):  
Weather Prediction ◽  
Heavy Precipitation ◽  
Mediterranean Area ◽  
Turbulent Fluxes ◽  
Western Mediterranean ◽  
Precipitation Event ◽  
Coupled Modes ◽  
Heavy Precipitation Event ◽  
Low Level ◽  
The Waves

Abstract. This study investigates the mechanisms acting at the air-sea interface during the heavy precipitation event that occurred between the 12–14 October 2016 over the north-western Mediterranean area, and that led to large amounts of rainfall (up to 300 mm in 24 h) over the Hérault region (South of France). The study case was characterized by a very strong easterly to southeasterly wind at low level (> 20 m/s) generating a very rough sea (significant wave height up to 6 m) along the French Riviera and the Gulf of Lion. In order to investigate the role of the waves on those air-sea exchanges during such extreme events a set of numerical experiments was designed using the Météo-France kilometer-scale AROME-France Numerical Weather Prediction model – including the WASP sea surface turbulent fluxes parametrization – and the wave model WaveWatchIII. Results from those sensitivity experiments in the forced or coupled modes showed that taking the waves generated by the model into account increases the surface roughness. Thus the easterly low-level atmospheric flow was slowed-down and the turbulent fluxes upstream of the precipitating system were significantly modified. This modified the forecast of the heaviest precipitation, notably in term of location.

scholarly journals Forcing mechanisms of a heavy precipitation event in the southeastern Adriatic area

2014 ◽  
Vol 72 (2) ◽  
pp. 1231-1252 ◽  
Author(s):  
Branka Ivančan-Picek ◽  
Kristian Horvath ◽  
Nataša Strelec Mahović ◽  
Marjana Gajić-Čapka
Keyword(s):  
Heavy Precipitation ◽  
Precipitation Event ◽  
Heavy Precipitation Event ◽  
Forcing Mechanisms

scholarly journals Dynamical contribution of mean potential vorticity pseudo-observations derived from MetOp/GOME2 ozone data into short-range weather forecast during high precipitation events

2015 ◽  
Vol 4 (2) ◽  
pp. 206
Author(s):  
Siham Sbii ◽  
Mimoun Zazoui ◽  
Noureddine Semane
Keyword(s):  
Potential Vorticity ◽  
Short Range ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Dynamical Behavior ◽  
Heavy Precipitation ◽  
Limited Area ◽  
Total Column Ozone ◽  
Ozone Data ◽  
Precipitation Events

<p>Satellites are uniquely capable of providing uniform data coverage globally. Motivated by such capability, this study builds on a previously described methodology that generates numerical weather prediction initial conditions from satellite total column ozone data. The methodology is based on two principal steps. Firstly, the studied linear regression between vertical (100hPa-500hPa) Mean Potential Vorticity (MPV) and MetOp/GOME2 total ozone data (O3) generates MPV pseudo-observations. Secondly, the 3D variational (3D-Var) assimilation method is designed to take into account MPV pseudo-observations in addition to conventional observations.</p><p>After a successful assimilation of MPV pseudo-observations using a 3D-Var approach within the Moroccan version of the ALADIN limited-area model, the present study aims to assess the dynamical behavior of the short-range forecast at upper levels during heavy precipitation events (HPEs). It is found that MPV assimilation offers the possibility to internally monitor the model upper-level dynamics in addition to the use of Water Vapor Satellite images.</p>

scholarly journals Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in southern Italy during HyMeX IOP 13: a modelling perspective

2019 ◽  
Vol 19 (11) ◽  
pp. 7487-7506
Author(s):  
Keun-Ok Lee ◽  
Franziska Aemisegger ◽  
Stephan Pfahl ◽  
Cyrille Flamant ◽  
Jean-Lionel Lacour ◽  
...  
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Heavy Precipitation ◽  
Convective Precipitation ◽  
Water Isotopes ◽  
Precipitation Event ◽  
Stable Water Isotopes ◽  
Heavy Precipitation Event ◽  
The North ◽  
Upper Level

Abstract. The dynamical context and moisture transport pathways embedded in large-scale flow and associated with a heavy precipitation event (HPE) in southern Italy (SI) are investigated with the help of stable water isotopes (SWIs) based on a purely numerical framework. The event occurred during the Intensive Observation Period (IOP) 13 of the field campaign of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) on 15 and 16 October 2012, and SI experienced intense rainfall of 62.4 mm over 27 h with two precipitation phases during this event. The first one (P1) was induced by convective precipitation ahead of a cold front, while the second one (P2) was mainly associated with precipitation induced by large-scale uplift. The moisture transport and processes responsible for the HPE are analysed using a simulation with the isotope-enabled regional numerical model COSMOiso. The simulation at a horizontal grid spacing of about 7 km over a large domain (about 4300 km ×3500 km) allows the isotopes signal to be distinguished due to local processes or large-scale advection. Backward trajectory analyses based on this simulation show that the air parcels arriving in SI during P1 originate from the North Atlantic and descend within an upper-level trough over the north-western Mediterranean. The descending air parcels reach elevations below 1 km over the sea and bring dry and isotopically depleted air (median δ18O ≤-25 ‰, water vapour mixing ratio q≤2 g kg−1) close to the surface, which induces strong surface evaporation. These air parcels are rapidly enriched in SWIs (δ18O ≥-14 ‰) and moistened (q≥8 g kg−1) over the Tyrrhenian Sea by taking up moisture from surface evaporation and potentially from evaporation of frontal precipitation. Thereafter, the SWI-enriched low-level air masses arriving upstream of SI are convectively pumped to higher altitudes, and the SWI-depleted moisture from higher levels is transported towards the surface within the downdrafts ahead of the cold front over SI, producing a large amount of convective precipitation in SI. Most of the moisture processes (i.e. evaporation, convective mixing) related to the HPE take place during the 18 h before P1 over SI. A period of 4 h later, during the second precipitation phase P2, the air parcels arriving over SI mainly originate from north Africa. The strong cyclonic flow around the eastward-moving upper-level trough induces the advection of a SWI-enriched African moisture plume towards SI and leads to large-scale uplift of the warm air mass along the cold front. This lifts moist and SWI-enriched air (median δ18O ≥-16 ‰, median q≥6 g kg−1) and leads to gradual rain out of the air parcels over Italy. Large-scale ascent in the warm sector ahead of the cold front takes place during the 72 h preceding P2 in SI. This work demonstrates how stable water isotopes can yield additional insights into the variety of thermodynamic mechanisms occurring at the mesoscale and synoptic scale during the formation of a HPE.

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