Gard Region Research Articles

Rare earth and alkali elements in stalagmites, as markers of Mediterranean environmental changes during Termination I

Speleothems represent a key source of information on climate variations in continental environments as they enable high temporal resolution reconstructions. The stalagmite salam3 presented in this study comes from the Salamandre Cave (SE France, Gard region). Its growth period, determined by 230Th/234U chronology and MOD-AGE extrapolation, falls between 10.91 ± 1.00 kyr BP and 13.43 ± 0.25 kyr BP, which corresponds to the transition between the last glacial period and the Holocene. This period is essential for the understanding of past and future climate variations.In this study, trace elements were measured along the growth axis of this stalagmite and results were compared with the elementary composition of bedrock and soil above the cave. Three periods were identified with high Li, Rb, Cs, Th and rare earth element (REE) concentrations, between 13.43 ± 0.25 and 13.11 ± 0.27, between 12.70 ± 0.34 and 12.30 ± 0.15 kyr, and between 11.31 ± 0.86 and 11.15 ± 0.87 kyr.Our results suggest that the alkali metals (alkalis) studied are either associated in the detrital phase with the clay and particle fraction (correlation with Th), or with the organic matter and colloids as complexed ligands (correlation with Mn). To attribute the origin of REE measured within the stalagmite, we compared their pattern with those of soil and bedrock, and two sources were deduced: i) periods with an enrichment in light REE and no cerium anomaly corresponding to mobilization from soil during weathering episodes such as the Bölling-Alleröd period; ii) from bedrock during a longer residence time of water in the epikarst such as during the Younger Dryas and the Holocene. Thus, as illustrated in this study, combined analysis of REE and alkalis can provide key information on soil weathering linked to climate/environmental change.

A Numerical Sensitivity Analysis of Soil Moisture Feedback on Convective Precipitation

AbstractOf the boundary conditions that affect the simulation of convective precipitation, soil moisture is one of the most important. In this study, we explore the impact of the soil moisture on convective precipitation, and factors affecting it, through an extensive numerical experiment based on four convective precipitation events that caused moderate to severe flooding in the Gard region of southern France. High-spatial-resolution (1 km) weather simulations were performed using the integrated atmospheric model Regional Atmospheric Modeling System/Integrated Community Limited Area Modeling System (RAMS/ICLAMS). The experimental framework included comparative analysis of five simulation scenarios for each event, in which we varied the magnitude and spatial distribution of the initial volumetric water content using realistic soil moisture fields with different spatial resolution. We used precipitation and surface soil moisture from radar and satellite sensors as references for the comparison of the sensitivity tests. Our results elucidate the complexity of the relationship between soil moisture and convective precipitation, showing that the control of soil water content on partitioning land surface heat fluxes has significant impacts on convective precipitation. Additionally, it is shown how different soil moisture conditions affect the modeled microphysical structure of the clouds, which translates into further changes in the magnitude and distribution of precipitation.

Assessing the Role of Spatial Rainfall Variability on Watershed Response based on Weather Radar Data (A Case Study of the Gard Region, France)

Assessing the Role of Spatial Rainfall Variability on Watershed Response based on Weather Radar Data (A Case Study of the Gard Region, France)

Assessment of commuters’ daily exposure to flash flooding over the roads of the Gard region, France

Summary Flash floods are responsible for a majority of natural disaster fatalities in the USA and Europe and most of them are vehicle-related. If human exposure to flood is generally assessed through the number of inhabitants per buildings located in flood prone zone, it is clear that this number varies dramatically throughout the day as people move from place to place to follow their daily program of activities. Knowing the number of motorists exposed on flood prone road sections or the factors determining their exposure would allow providing a more realistic evaluation of the degree of exposure. In order to bridge this gap and provide emergency managers with methods to assess the risk level for motorists, this paper describes two methods, a simple rough-and-ready estimate and a traffic attribution method, and applies both of them on datasets of the Gard departement, an administrative region of Southern France with about 700 000 inhabitants over 5875 km2. The first method to obtain an overall estimation of motorists flood exposure is to combine (i) the regional density of roads and rivers to derive a count of potential road cuts and (ii) the average daily kilometers driven by commuters of the study area to derive the number of people passing these potential cuts. If useful as a first approximation, this method fails to capture the spatial heterogeneities introduced by the geometry of river and road networks and the distribution of commuters’ itineraries. To address this point, this paper (i) uses a pre-established detailed identification of road cuts (Naulin et al., 2013) and (ii) applies a well-known traffic attribution method to existing and freely available census datasets. Both methods indicate that commuters’ exposure is much larger than the number of commuters itself, illustrating the risk amplification effect of mobility. Comparing the results from both methods shows that (i) the road network geometry plays a significant role in reducing the risk of river-road dangerous intersections and (ii) not all commuters are equally exposed. Evidently commuters who have longer routes are more exposed, but residents of rural municipalities as well as professionals with highly qualified jobs are also more exposed. Finally, these exposure assessment methods applied to the Gard area allows locating road sections where commuters’ exposure to flood is high. It also sets the first step toward the implementation of a modeling platform able to combine the estimation of daily travel patterns exposure and behavioral response of motorists to road flooding, a critical input for emergency services and services in charge of the management of road networks in flash flood prone areas.

Regional models for distributed flash-flood nowcasting: towards an estimation of potential impacts and damages

Flash floods monitoring systems developed up to now generally enable a real-time assessment of the potential flash-floods magnitudes based on highly distributed hydrological models and weather radar records. The approach presented here aims to go one step ahead by offering a direct assessment of the potential impacts of flash floods on inhabited areas. This approach is based on an a priori analysis of the considered area in order (1) to evaluate based on a semi-automatic hydraulic approach (Cartino method) the potentially flooded areas for different discharge levels, and (2) to identify the associated buildings and/or population at risk based on geographic databases. This preliminary analysis enables to build a simplified impact model (discharge-impact curve) for each river reach, which can be used to directly estimate the importance of potentially affected assets based on the outputs of a distributed rainfall-runoff model. This article presents a first case study conducted in the Gard region (south eastern France). The first validation results are presented in terms of (1) accuracy of the delineation of the flooded areas estimated based on the Cartino method and using a high resolution DTM, and (2) relevance and usefulness of the impact model obtained. The impacts estimated at the event scale will now be evaluated in a near future based on insurance claim data provided by CCR (Caisse Centrale de Reassurrance).

Spatially distributed flood forecasting in flash flood prone areas: Application to road network supervision in Southern France

Summary Accurate flood forecasts are critical to an efficient flood event management strategy. Until now, hydro-meteorological forecasts have mainly been used to establish early-warnings in France (meteorological and flood vigilance maps) or over the world (flash-flood guidances). These forecasts are typically limited either to the main streams covered by the flood forecasting services or to watersheds with specific assets like check dams, which in most cases are well gauged river sections, thus leaving aside large parts of the territory. This paper presents a distributed hydro-meteorological forecasting approach, which makes use of the high spatial and temporal resolution rainfall estimates that are now available, to provide information at ungauged sites. The proposed system intended to detect road inundation risks had initially been developed and tested in areas of limited size. This paper presents the extension of such a system to an entire region (i.e. the Gard region in Southern France), including over 2000 crossing points between rivers and roads and its validation with respect to a large data set of actual reported road inundations observed during recent flash flood events. These initial validation results appear to be most promising. The eventual proposed tool would provide the necessary information for flood event management services to identify the areas at risk and adopt appropriate safety and rescue measures: i.e. pre-positioning of rescue equipment, interruption of the traffic on the exposed roads and determination of safe access or evacuation routes. Moreover, beyond the specific application to the supervision of a road network, the research undertaken herein also provides results for the performance of hydro-meteorological forecasts on ungauged headwaters.

George Desvallières et la Grande Guerre

George Desvallières (1861-1950) took part in the 1914-18 War as battalion commander with the “Bataillon Des Vosges”, and depicted its tragic history on his return from the front. From 1883, he became a fully recognised artist with his painting being presented at all major Paris exhibitions. Founder, Vice-President, then President of the “Salon d’Automne”, he became known as a discoverer of young talents, and obtained recognition for both cubists and fauvists. At the start of the First World War, Desvallières joined up as a volunteer. Very quickly his men acknowledged him to be an unsurpassed leader, and demanded of his superiors that he be kept in his post, which was at first only a temporary appointment. Desvallières led his “chasseurs” across the Alsatian mountains for four years with determination, courage and a kindness recognised by all on the front. In March 1915, his seventeen-year- old son Daniel was killed in action a few miles away from his father. This loss affected him deeply, but thanks to his convert’s faith, he was able to sublimate this terrible ordeal. All his post-war work is centred on the theme of the soldier’s sacrifice for his country, which he assimilates to the sacrifice of Christ on the Cross. Some of his canvases are directly related to the War and to his son’s death, and his impressive wall-paintings on a similar theme made a profound impact on contemporary public opinion. The “Drapeau du Sacré-Coeur” (Banner of the Sacred Heart) at the Church of Notre Dame de Verneuil (1919) was the starting point for these murals. There followed such monumental works of pictorial expression as the Saint Privat Chapel in the Gard region (1920-1925), which will be discussed in this paper, the stained-glass windows at the Douaumont Ossuary (1927), the decoration of Wittenheim Church in Alsace (1929-1931), the Chapel of the Cité Saint Yves (1931) and the Way of the Cross at the Holy Spirit Church (1935) in Paris.* “George” without the “s” because of his Scottish ancestry.

Use of radar rainfall estimates and forecasts to prevent flash flood in real time by using a road inundation warning system

Important damages occur in small headwater catchments when they are hit by severe storms with complex spatio-temporal structure, sometimes resulting in flash floods. As these catchments are mostly not covered by sensor networks, it is difficult to forecast these floods. This is particularly true for road submersions, representing major concerns for flood event managers. The use of Quantitative Precipitation Estimates and Forecasts (QPE/QPF) especially based on radar measurements could particularly be adequate to evaluate rainfall-induced risks. Although their characteristic time and space scales would make them suitable for flash flood modelling, the impact of their uncertainties remain uncertain and have to be evaluated. The Gard region (France) has been chosen as case study. This area is frequently affected by severe flash floods, and an application devoted to the road network has also been recently developed for the North part of this region. This warning system combines distributed hydro-meteorological modelling and susceptibility analysis to provide warnings of road inundations. The warning system has been tested on the specific storm of the 29–30 September 2007. During this event, around 200 mm dropped on the South part of the Gard and many roads were submerged. Radar-based QPE and QPF have been used to forecast the exact location of road submersions and the results have been compared to the effective road submersions actually occurred during the event as listed by the emergency services. Used on an area it has not been calibrated, the results confirm that the road submersion warning system represents a promising tool for anticipating and quantifying the consequences of storm events at ground. It rates the submersion risk with an acceptable level of accuracy and demonstrates also the quality of high spatial and temporal resolution radar rainfall data in real time, and the possibility to use them despite their uncertainties. However because of the quality of rainfall forecasts falls drastically with time, it is not often sufficient to provide valuable information for lead times exceeding 1 h.

Application of a distributed hydrological model to the design of a road inundation warning system for flash flood prone areas

Abstract. This paper presents an initial prototype of a distributed hydrological model used to map possible road inundations in a region frequently exposed to severe flash floods: the Gard region (South of France). The prototype has been tested in a pseudo real-time mode on five recent flash flood events for which actual road inundations have been inventoried. The results are promising: close to 100% probability of detection of actual inundations, inundations detected before they were reported by the road management field teams with a false alarm ratios not exceeding 30%. This specific case study differs from the standard applications of rainfall-runoff models to produce flood forecasts, focussed on a single or a limited number of gauged river cross sections. It illustrates that, despite their lack of accuracy, hydro-meteorological forecasts based on rainfall-runoff models, especially distributed models, contain valuable information for flood event management. The possible consequences of landslides, debris flows and local erosion processes, sometimes associated with flash floods, were not considered at this stage of development of the prototype. They are limited in the Gard region but should be taken into account in future developments of the approach to implement it efficiently in other areas more exposed to these phenomena such as the Alpine area.

Assessment of the susceptibility of roads to flooding based on geographical information – test in a flash flood prone area (the Gard region, France)

Abstract. In flash flood prone areas, roads are often the first assets affected by inundations which make rescue operations difficult and represent a major threat to lives: almost half of the victims are car passengers trapped by floods. In the past years, the Gard region (France) road management services have realized an extensive inventory of the known road submersions that occurred during the last 40 years. This inventory provided an unique opportunity to analyse the causes of road flooding in an area frequently affected by severe flash floods. It will be used to develop a road submersion susceptibility rating method, representing the first element of a road warning system. This paper presents the results of the analysis of this data set. A companion paper will show how the proposed road susceptibility rating method can be combined with distributed rainfall-runoff simulations to provide accurate road submersion risk maps. The very low correlation between the various possible explanatory factors and the susceptibility to flooding measured by the number of past observed submersions implied the use of particular statistical analysis methods based on the general principals of the discriminant analysis. The analysis led to the definition of four susceptibility classes for river crossing road sections. Validation tests confirmed that this classification is robust, at least in the considered area. One major outcome of the analysis is that the susceptibility to flooding is rather linked to the location of the road sections than to the size of the river crossing structure (bridge or culvert).

The use of distributed hydrological models for the Gard 2002 flash flood event: Analysis of associated hydrological processes

This paper presents a detailed analysis of the September 8-9 2002 flash flood event in the Gard region (southern France) using two distributed hydrological models: CVN built within the LIQUID® hydrological platform and MARINE. The models differ in terms of spatial discretization, infiltration and water redistribution representation, and river flow transfer. MARINE can also account for sub-surface lateral flow. Both models are set up using the same available information, namely a DEM and a pedology map. They are forced with high resolution radar rainfall data over a set of 18 sub-catchments ranging from 2.5 to 99 km2 and are run without calibration. To begin with, models simulations are assessed against post field estimates of the time of peak and the maximum peak discharge showing a fair agreement for both models. The results are then discussed in terms of flow dynamics, runoff coefficients and soil saturation dynamics. The contribution of the sub-surface lateral flow is also quantified using the MARINE model. This analysis highlights that rainfall remains the first controlling factor of flash flood dynamics. High rainfall peak intensities are very influential of the maximum peak discharge for both models, but especially for the CVN model which has a simplified overland flow transfer. The river bed roughness also influences the peak intensity and time. Soil spatial representation is shown to have a significant role on runoff coefficients and on the spatial variability of saturation dynamics. Simulated soil saturation is found to be strongly related with soil depth and initial storage deficit maps, due to a full saturation of most of the area at the end of the event. When activated, the signature of sub-surface lateral flow is also visible in the spatial patterns of soil saturation with higher values concentrating along the river network. However, the data currently available do not allow the assessment of both patterns. The paper concludes with a set of recommendations for enhancing field observations in order to progress in process understanding and gather a larger set of data to improve the realism of distributed models.

Distributed hydrologic and hydraulic modelling with radar rainfall input: Reconstruction of the 8–9 September 2002 catastrophic flood event in the Gard region, France

On 8–9 September 2002, an extreme rainfall event caused by a stationary mesoscale convective system (MCS) occurred in the Gard region, France. Distributed hydrologic and hydraulic modelling has been carried out to assess and compare the various sources of data collected operationally and during the post-event field surveys. Distributed hydrological modelling was performed with n-TOPMODELs and assessed for ungauged basins with the discharge estimates of the post-event surveys. A careful examination of the occurrence in time and space of the flash floods over the head watersheds indicates that flooding was controlled by the trajectory of the convective part of the MCS. Stationarity of the MCS over the Gardon watershed (1858 km 2 at Remoulins) for 28 h was responsible for the exceptional magnitude of the flood at this scale. The flood dynamics were characterized by an extensive inundation of the Gardonnenque plain upstream of the Gardon Gorges resulting in a significant peak flow reduction downstream. One-dimensional unsteady-flow hydraulic modelling was found to be required to reproduce these dynamics. Hydraulic modelling also proved to be potentially useful for the critical analysis and extrapolation of operational discharge rating curves.

A modeling approach to assess the hydrological response of small mediterranean catchments to the variability of soil characteristics in a context of extreme events

Abstract. This paper presents a modeling study aiming at quantifying the possible impact of soil characteristics on the hydrological response of small ungauged catchments in a context of extreme events. The study focuses on the September 2002 event in the Gard region (South-Eastern France), which led to catastrophic flash-floods. The proposed modeling approach is able to take into account rainfall variability and soil profiles variability. Its spatial discretization is determined using Digital Elevation Model (DEM) and a soil map. The model computes infiltration, ponding and vertical soil water distribution, as well as river discharge. In order to be applicable to ungauged catchments, the model is set up without any calibration and the soil parameter specification is based on an existing soil database. The model verification is based on a regional evaluation using 17 estimated discharges obtained from an extensive post-flood investigation. Thus, this approach provides a spatial view of the hydrological response across a large range of scales. To perform the simulations, radar rainfall estimations are used at a 1 km2 and 5 min resolution. To specify the soil hydraulic properties, two types of pedotransfer function (PTF) are compared. It is shown that the PTF including information about soil structure reflects better the spatial variability that can be encountered in the field. The study is focused on four small ungauged catchments of less than 10 km2, which experienced casualties. Simulated specific peak discharges are found to be in agreement with estimations from a post-event in situ investigation. Examining the dynamics of simulated infiltration and saturation degrees, two different behaviors are shown which correspond to different runoff production mechanisms that could be encountered within catchments of less than 10 km2. They produce simulated runoff coefficients that evolve in time and highlight the variability of the infiltration capacity of the various soil types. Therefore, we propose a cartography distinguishing between areas prone to saturation excess and areas prone only to infiltration excess mechanisms. The questions raised by this modeling study will be useful to improve field observations, aiming at better understanding runoff generation for these extreme events and examine the possibility for early warning, even in very small ungauged catchments.

Chemical and isotopic investigation of rainwater in Southern France (1996–2002): Potential use as input signal for karst functioning investigation

Several recharge processes may be defined for karst systems. However, their respective influence is difficult to determine from spring-water chemistry without a good knowledge of the input signal, i.e. rainfall chemistry. Given the little data published concerning rainfall chemistry in the French Mediterranean area, two rainfall gauges networks were installed – one along a transect from the Mediterranean coast to the most elevated part of the Hérault region, which was monitored over two hydrological cycles (1996–1998), and a second on the catchment area of the main karst aquifer of the Gard region (Fontaine de Nîmes karst system), which was monitored over four hydrological cycles (1998–2002). The main objective of this study was to characterize the input signal of Mediterranean karst systems by analysing the chemical and isotopic compositions of rainfall, in particular with reference to spatial, intra-seasonal and inter-annual variations. Rainwater samples were collected and analysed for major ions, trace elements (B, Br and Sr) and stable water isotopes ( δ 18 O, δ 2 H). The major results of this study are the following: the degree of fluctuation in concentrations of major elements and stable water isotopes in the rainwater depend strongly on elevation and distance from sea. Higher rainfall concentrations are systematically associated with areas nearest to the Mediterranean coast. Rainfall of Atlantic and Mediterranean origins may be differentiated – rainfall of Mediterranean origin is characterized by a higher deuterium excess and generally enriched in heavy isotopes. This rainfall is predominant during the autumn.

Human exposure to flash floods – Relation between flood parameters and human vulnerability during a storm of September 2002 in Southern France

The aim of this paper is to investigate the detailed hydrometeorological circumstances that lead to accidental casualties, and to better understand the prominent physical factors of risk. Based on an event that affected the Gard region (Southern France) in September 2002, it is a first attempt to combine analysis of the physical and human response to Mediterranean storms. After details concerning the methodology (for meteorological, hydrological and casualty analysis), the local context and the event, the authors examine two points: the dynamics of the event (flash-flood and riverine-flood response to the storm) together with human exposure on the one hand, and scale as a critical problem affecting flood risk on the other. This investigation stresses the specificity of small catchments, which are more dangerous both in hydrological and human terms. Moreover, this contribution linking social sciences and geophysics constitutes an important step in what [Morss, R.E., Wilhelmi, O.V., Downton, M.W., Gruntfest, E., 2005. Flood risk, uncertainty, and scientific information for decision making. Bull. Am. Meteor. Soc. 86 (11), 1593–1601] call the “End to end to end” process

The 8 and 9 September 2002 flash flood event in France: a model intercomparison

Abstract. Within the framework of the European Interreg IIIb Medocc program, the HYDROPTIMET project aims at the optimization of the hydrometeorological forecasting tools in the context of intense precipitation within complex topography. Therefore, some meteorological forecast models and hydrological models were tested on four Mediterranean flash-flood events. One of them occured in France where the South-eastern ridge of the French "Massif Central", the Gard region, experienced a devastating flood on 8 and 9 September 2002. 24 people were killed during this event and the economic damage was estimated at 1.2 billion euros. To built the next generation of the hydrometeorological forecasting chain that will be able to capture such localized and fast events and the resulting discharges, the forecasted rain fields might be improved to be relevant for hydrological purposes. In such context, this paper presents the results of the evaluation methodology proposed by Yates et al. (2005) that highlights the relevant hydrological scales of a simulated rain field. Simulated rain fields of 7 meteorological model runs concerning with the French event are therefore evaluated for different accumulation times. The dynamics of these models are either based on non-hydrostatic or hydrostatic equation systems. Moreover, these models were run under different configurations (resolution, initial conditions). The classical score analysis and the areal evaluation of the simulated rain fields are then performed in order to put forward the main simulation characteristics that improve the quantitative precipitation forecast. The conclusions draw some recommendations on the value of the quantitative precipitation forecasts and way to use it for quantitative discharge forecasts within mountainous areas.

The Catastrophic Flash-Flood Event of 8–9 September 2002 in the Gard Region, France: A First Case Study for the Cévennes–Vivarais Mediterranean Hydrometeorological Observatory

Abstract The Cévennes–Vivarais Mediterranean Hydrometeorological Observatory (OHM-CV) is a research initiative aimed at improving the understanding and modeling of the Mediterranean intense rain events that frequently result in devastating flash floods in southern France. A primary objective is to bring together the skills of meteorologists and hydrologists, modelers and instrumentalists, researchers and practitioners, to cope with these rather unpredictable events. In line with previously published flash-flood monographs, the present paper aims at documenting the 8–9 September 2002 catastrophic event, which resulted in 24 casualties and an economic damage evaluated at 1.2 billion euros (i.e., about 1 billion U.S. dollars) in the Gard region, France. A description of the synoptic meteorological situation is first given and shows that no particular precursor indicated the imminence of such an extreme event. Then, radar and rain gauge analyses are used to assess the magnitude of the rain event, which was particularly remarkable for its spatial extent with rain amounts greater than 200 mm in 24 h over 5500 km2. The maximum values of 600–700 mm observed locally are among the highest daily records in the region. The preliminary results of the postevent hydrological investigation show that the hydrologic response of the upstream watersheds of the Gard and Vidourle Rivers is consistent with the marked space–time structure of the rain event. It is noteworthy that peak specific discharges were very high over most of the affected areas (5–10 m3 s−1 km−2) and reached locally extraordinary values of more than 20 m3 s−1 km−2. A preliminary analysis indicates contrasting hydrological behaviors that seem to be related to geomorphological factors, notably the influence of karst in part of the region. An overview of the ongoing meteorological and hydrological research projects devoted to this case study within the OHM-CV is finally presented.

Un centre domanial dans la vallée de la Tave : la villa de Mayran (Saint-Victor-la-Coste, Gard)

Since the last decade, archaeology of the villa has a renewal of interest in the French department of Gard. The publication of the excavations and prospections realized on the site of Mayran (St Victor La Coste) reflects the dynamism of this research. One of the most interesting results is the historical reconstruction of the site on a long period of time, i.e. from the Ist century BC up to present time. During the Roman period, the villa was a large complex including, in the Late Empire, a wine-making equipment and an acqueduct with an uncommon morphology. The period of occupation extends from Early Middle Age (VIth-Xth century) up to the High Middle Age (XIth-XIIIth century). The Mayran villa gives us an example of an important characteristic of the villae in the Gard region : their lasting role in the organization of the countryside.

GPS monitoring of the tropospheric water vapor distribution and variation during the 9 September 2002 torrential precipitation episode in the Cévennes (southern France)

On 8–9 September 2002, torrential rainfall and flooding hit the Gard region in southern France causing extensive damages and casualties. This is an exceptional example of a so‐called Cévenol episode with 24 hour cumulative rainfall up to about 600 mm at some places and more than 200 mm over a large area (5500 km2). In this work we have used GPS data to determine integrated water vapor (IWV) as well as horizontal wet gradients and residuals. Using the IWV, we have monitored the evolution of the convective system associated with the rainfall from the water vapor accumulation stage through the stagnation of the convective cell and finally to the breakup of the system. Our interpretation of the GPS meteorological parameters is supported by synoptic maps, numerical weather analyses, and rain images from meteorological radars. We have evidenced from GPS data that this heavy precipitation is associated with ongoing accumulation of water vapor, even through the raining period, but that rain stopped as soon as the weather circulation pattern changed. The evolution of this event is typical in the context of the Cévenol meteorology. Furthermore, we have shown that the horizontal wet gradients help describe the heterogeneity of the water vapor field and holds information concerning the passage of the convective system. Finally, we have noticed that the residuals, which in theory should be proportional to water vapor heterogeneity, were also highly perturbed by the precipitation itself. In our conclusions we discuss the interest of a regional GPS network for monitoring and for future studies on water vapor tomography.

Jean Valade's Portraits of the Faventines Family

RésuméThe Faventines family, from Le Vigan in the Gard region of France, pursued a path very similar to that of other local financiers such as the Peyrenc de Moras family. Pierre Faventines left his native town for Paris, where he became treasurer of the estates of the house of Bourbon and later a fermier general. His second son, Jean‐Maurice Faventines de Fontenilles, followed him, becoming his assistant in 1764. The children in the family made important alliances, acquiring the houses, lands, titles and possessions of the old aristocracy; at the same time, they mixed with the money of other nouveaux riches such as Baudard de Sainte‐James, whose sister Fontenilles married. It was in the pursuit of this grand social and economic ambition that they commissioned Jean Valade to execute a large number of family portraits, works which display little of the psychological treatment favoured by Valade's rivals but which instead reflect his subjects' aspirations through their vibrant colouring. This whole world foundered with the Revolution: the family's chateaux were largely destroyed or abandoned; their furniture was scattered without trace; and only this extraordinary series of portraits by Valade survives to commemorate this magnificence which was the object of so much admiration in the eighteenth century.