Caractérisation de l'aléa climatique pluvieux en région méditerranéenne : analyse statistique des surfaces pluvieuses

Ces 10 dernières années, certains épisodes pluvieux marquants ont entraîné une prise de conscience du risque encouru par les agglomérations modernes face à des phénomènes hydrologiques particuliers. La gestion du risque pluvial passe par une amélioration de la connaissance de l'aléa pluvieux. Dans cet article, on développe une approche stochastique exploitant le potentiel d'informations contenu dans un échantillon d'épisodes pluvieux extrêmes ayant ou ayant pu engendrer des crues dévastatrices. Une approche spatiale est utilisée pour caractériser l'aléa pluvieux. A partir d'un jeu d'épisodes extrêmes sélectionnés sur une région méditerranéenne entre 1958 et 1993, on estime l'aire des surfaces où les précipitations dépassent un seuil de pluviométrie fixé. L'estimation des aires des surfaces pluvieuses nécessite le recours à un modèle d'interpolation spatiale des hauteurs de pluie. La justification du krigeage climatologique est présentée ainsi que l'estimation des paramètres du modèle retenu. Les distributions des aires des isohyètes, à différents seuils de pluviométrie, sont ensuite analysées. Il apparaît que quelle que soit l'isohyète considérée, une loi gamma peut être ajustée sur l'échantillon de surface. Une relation entre les paramètres des lois permet une généralisation du modèle probabiliste à n'importe quel seuil de pluie compris entre 50 et 300 mm.In the last 10 years many cities in southern Europe have been affected by heavy rainfall events leading to severe runoffs. The assessment of rainfall risk requires a better knowledge of the climate hazards and particularly rainfall hazards. The most usual rainfall risk assessment is based on a stochastic approach and point rainfall frequency analysis remains the most-used method. However, in the Mediterranean region great variations of rainfall depth frequencies can be observed according to the point considered, and according to the period of observation. Moreover the recent hydrological catastrophes which have affected the south of France have been studied on an individual basis and studies based on a global approach, using the whole information contained in a sample of several observations, remain unusual.A rainfall risk assessment has been proposed in the Languedoc-Roussillon, a 28,000 km2 region along the Mediterranean sea. This study has been based on a sample of 93 daily extreme rainfall events, which have occurred in the region. They have been extracted from the Météo-France database for the 1958-1993 period of observation, if a rainfall depth greater or equal to 190 mm in 24 hours or 48 hours (because of the sampling constraints) has been observed at one rain gauge in the region at least. The spatial extension of the rainy surfaces defined at different rainfall thresholds, varying from 50 to 250 mm/24 hours and 50 to 300 mm/48 hours, have been investigated. For a given threshold, the area of the rainy surface corresponding to a given frequency has been estimated.The estimation of the rainy surfaces area has required the choice of a spatial interpolation method: the climatological kriging method has been used. This method is based on the assumption that all the rainfall events came from the same meteorological situation, but some studies have shown that there may be different meteorological situations (TOURASSE, 1981; RIVERAIN, 1997). Thus the sensitivity of the interpolation model according to this assumption has been tested. A different interpolation model has been estimated for each season because the information about the meteorological situations which have generated the selected events is not available. Only the variogram over June to August differs significantly from the "annual" variogram. The differences between the rainy surfaces area estimated with the "seasonal" variogram and the "annual" one did not exceed 10% in proportion of the areas estimated with the "annual" variogram. The rainy surface areas are less sensitive to the climatological assumption. For each time step and each rainfall threshold considered, it has been observed that the two parameter Gamma law could best fit the frequencies of the rainy surface areas. The relation between each of the Gamma law parameters and the rain threshold has been estimated (relations R1 and R2). The quantiles of the rainy surface areas have been estimated with two methods :- directly from the fitting of a Gamma function to the sample of rainy surface areas; - using the previous relation to estimate the Gamma function parameters. It has been observed that the quantiles estimated with the second method were close to those estimated with the first method, even if the fitting errors of the R1 and R2 relations were considered. Such a result allows one to estimate the regional frequency of a rainy surface areas defined at each threshold between 50 and 300 mm/48 hours or 50 and 250 mm/24 hours. However extrapolations beyond the studied threshold intervals should not be done because the R1 and R2 relations are empirical.The isohyets area quantiles have been defined: they represent the isohyet area corresponding to a given rainfall threshold and a given return period. The isohyet area quantiles may be very large; for example at the 200 mm / 48 hours threshold the isohyets area represents 15% of the region (4500 km2). This can be explained by the time step dt. The isohyets area represents the dynamics of the convective cells integrated over dt, which remains unknown but is greater than 48 hours. Moreover for a given rainfall threshold and a given event, several separate isohyets could be observed. However in this study only the all areas corresponding to the different isohyets have been estimated. Thus it could give a very large area when the event affects the all region.The ratio between the isohyet area quantiles at the 48-hour and 24-hour time steps evolved from 1.3 to 20: it increased with the rainfall threshold for a given return period. This can be explained by the strong dynamics of the convective cells which generate the highest rainfall depths, compared to the rain cells at a larger spatial scale, which generate lower rainfall depths. Thus the isohyet areas defined at a high rainfall threshold are sensitive to the time steps than isohyet areas defined at a smaller rainfall threshold.The frequencies estimated in this study have been regional frequencies, but it appears that the isohyet areas are not independent of the event's location. However, at this stage the sample is too small to allow a study of conditional frequencies. In order to perform this study the sample has already been enlarged by considering all the French Mediterranean region which have been affected by heavy rainfall depths. It has been based on all the information included in the Météo-France data base over this region (since 1870). The rainfall threshold used to select the rainfall events has been diminished to 90 mm/ 24 hours to include the high intensity events over short time steps which could generated severe floods, especially over small catchments.Combined with the information about the meteorological situations, the development of this work should allow improved studies of the relations between the rainy surfaces and the meteorological situations at the origin of the rainfall events

Influence de l'évolution dans l'espace et le temps d'un réseau de pluviomètres sur l'observation des surfaces de pluie en fonction de leur aire

La caractérisation précise de l'aléa climatique nécessite l'exploitation de mesures reposant sur la période d'observation la plus longue possible. Souvent cette information est constituée de mesures au sol à partir de postes pluviométriques. L'évolution dans l'espace et dans le temps des réseaux de pluviomètres introduit un biais dans toute étude stochastique spatiale ou ponctuelle reposant sur des séries de valeurs échantillonnées à partir d'un tel réseau. On se propose dans cet article de quantifier la potentialité d'un réseau de pluviomètres à intercepter des surfaces de pluie, en fonction de leur aire et des caractéristiques de ce réseau à une date donnée. On procède par simulation à partir du réseau de pluviomètres géré par Météo-France sur la région Languedoc-Roussillon, étudié sur une période de 123 ans. On définit la notion de pourcentage d'observation, qui représente la proportion de surface pluvieuse affectant la région et qui ont été interceptées par le réseau de mesure. Toutes études statistique reposant sur des séries de mesure échantillonnées à partir du réseau seront biaisées, étant donné qu'entre 1958 et 1993, on observe qu'une proportion des surfaces pluvieuses de moins de 2000 km2 qui ont touché la région étudiée. Ce pourcentage d'observation est ensuite utilisé pour débiaiser les estimations de l'aléa pluvieux régional reposant sur le réseau de pluviomètres.The most usual rainfall risk assessment, based on a stochastic approach, or an accurate quantiles estimation, requires long series of observations. Most of the time when long periods of observation are considered, the available information consists of data from daily rain gauge networks which are evolving in space and time during these periods. As the rainy surfaces which generate the highest intensities are localised in space, the intergauge distances may be too large to "observe" all the rainfall events occurring over a given network. Thus it could bias the stochastic results based on values sampled from such a network, especially when extreme rainfall events are considered. The aim of this paper is to estimate the capacity of a daily rain gauge network to intercept rainy surfaces according to their area and the network density. The results have been used to estimate the bias introduced in rainfall risk assessment using the regional frequencies of isohyets areas observed in the studied region.The network studied is the Languedoc-Roussillon daily rain gauge network, in a French region along the Mediterranean sea. The network has been developed by Météo-France since 1870. The number of gauges put into service has varied during the 1870-1993 period of observation: from 3 gauges in 1870, the maximum reached was 353 gauges in 1969 and 1972, which represented a spatial mean density of 12.6 gauges/ 1000 km2. Since 1972 the number of gauges has decreased; in 1993 the gauge density was the same as in 1963, with 10.6 gauges/ 1000 km2. Nevertheless the clustered gauges have been reduced, as have the maximum intergauge distances, and the network has become more homogeneous over the region.Using simulation, the percentage of rainy surfaces which have affected the region, and which have been observed by the rain gauge network, has been estimated, as a function of the rainy surfaces area and the rain gauge density. It could be interpreted as the empirical expression of the probability to observe a given rainy surface with a given network configuration. Two periods have been considered, 1870-1957 and 1958-1993. Two simulation methods have been used: in the first the rainy surfaces have been considered to be static and in the second their motion has been taken into account. It has appeared that considering the motion of rainy surfaces yields the same results as the static method but with a different rainy surface geometry. The small differences between the percentage of rainy surfaces observed by the network in both cases can be explained by the simulation methods. It has been shown that the average probability over the period from 1870 to 1957 of observing a given rainy surface is 2 to 4 times less than the average probability over the 1958-1993 observation period, during which the gauge density has increased and the network has become more homogeneous over the region: over the 1870-1957 period the rain gauge network intercepted 50% at least of the rainy surfaces equal to or larger than 700 km2 but in the 1958-1993 period 50% at least of the rainy surfaces were observed if their area exceeded 80 km2. If the rainfall event which affected the N"mes hydrological system on 2-3 October 1988 is considered, these results have shown that the average probability over the 1870-1957 observation period to observe such an event is 2 times less than over the 1958-1993 observation period.In a recent study, a rainfall risk assessment has been made over the Languedoc-Roussillon region, using the frequencies of the isohyets areas defined for different rain thresholds, for 24-hour and 48-hour durations. These isohyets areas have been estimated on the basis of a sample of 93 rainfall events selected over the Languedoc-Roussillon region from 1958 to 1993 (Neppel et al., 1998). A method to estimate the bias introduced by the network in the estimation of the isohyets area return periods has been carried out, using this empirical probability estimated with the static simulation method. It has been shown that the bias only affects the more frequent isohyets area quantiles, corresponding to return period of 1 year for 48-hour duration and 1 to 3 years for 24-hour duration. Moreover, for this sample and this network, it has been shown that the bias would be negligible compared to the quantiles 5% confidence limits, whatever the return period and the time step. It must be noted that with this sample the 5% confidence limits of the quantiles sometimes reach 100% of the quantiles. The results are related to the sample and the network configuration, and they should not be extended to other areas or other samples: a larger sample over the same region could lead to narrower confidence limits, in which case the bias might no longer be negligible. In particular, the use of historical data needs to consider the longest observation period. Usually the rain gauge density decreases over such observation periods, which leads to a lower empirical probability of observing rainy surfaces according to their area. Thus the bias influence may increase, especially compared with the quantiles 5% confidence limits which are reduced when the sample is enlarged. Nevertheless the method described here is general and may be transposed to other geographical zones, provided that the isohyets area frequencies and the empirical probability of observing a rainy surface according to its area, corresponding to the network under consideration, are known.The current tendency in France is to reduce the number of daily rain gauges, managed by volunteers, and to replace them by automatic rain gauges. However in such a case the density would decrease and reach that observed in 1900. When rainfall risk assessment is considered, this study has shown the drawbacks of such a policy

Novel regulators of stem cell fates identified by a multivariate phenotype screen of small compounds on human embryonic stem cell colonies

Understanding the complex mechanisms that govern the fate decisions of human embryonic stem cells (hESCs) is fundamental to their use in cell replacement therapies. The progress of dissecting these mechanisms will be facilitated by the availability of robust high-throughput screening assays on hESCs. In this study, we report an image-based high-content assay for detecting compounds that affect hESC survival or pluripotency. Our assay was designed to detect changes in the phenotype of hESC colonies by quantifying multiple parameters, including the number of cells in a colony, colony area and shape, intensity of nuclear staining, and the percentage of cells in the colony that express a marker of pluripotency (TRA-1-60), as well as the number of colonies per well. We used this assay to screen 1040 compounds from two commercial compound libraries, and identified 17 that promoted differentiation, as well as 5 that promoted survival of hESCs. Among the novel small compounds we identified with activity on hESC are several steroids that promote hESC differentiation and the antihypertensive drug, pinacidil, which affects hESC survival. The analysis of overlapping targets of pinacidil and the other survival compounds revealed that activity of PRK2, ROCK, MNK1, RSK1, and MSK1 kinases may contribute to the survival of hESCs. (C) 2010 Elsevier B.V. All rights reserved

Evoked itch perception is associated with changes in functional brain connectivity

Chronic itch, a highly debilitating condition, has received relatively little attention in the neuroimaging literature. Recent studies suggest that brain regions supporting itch in chronic itch patients encompass sensorimotor and salience networks, and corticostriatal circuits involved in motor preparation for scratching. However, how these different brain areas interact with one another in the context of itch is still unknown. We acquired BOLD fMRI scans in 14 atopic dermatitis patients to investigate resting-state functional connectivity before and after allergen-induced itch exacerbated the clinical itch perception in these patients. A seed-based analysis revealed decreased functional connectivity from baseline resting state to the evoked-itch state between several itch-related brain regions, particularly the insular and cingulate cortices and basal ganglia, where decreased connectivity was significantly correlated with increased levels of perceived itch. In contrast, evoked itch increased connectivity between key nodes of the frontoparietal control network (superior parietal lobule and dorsolateral prefrontal cortex), where higher increase in connectivity was correlated with a lesser increase in perceived itch, suggesting that greater interaction between nodes of this executive attention network serves to limit itch sensation via enhanced top-down regulation. Overall, our results provide the first evidence of itch-dependent changes in functional connectivity across multiple brain regions

Chapter X: The Tour de France: a success story in spite of competitive imbalance and doping

International audienceThe chapter goes as follows. In the first section it is demonstrated how the Tour de France is a high quality product. This is a result from its accurate design, its management, its economic model and its finance structure, both in comparison to other mega-sporting events and with reference to tournament theory. It is not easy to assess the competitive balance in the Tour de France since, as was demonstrated in chapter 10, it is at the same time an individual and a team sport contest. After reviewing some results published in literature so far, a new metrics for evaluating competitive balanced in the Tour de France is presented in section 2. Finally, the Tour de France cannot ignore doping as a potential threat to fan attendance and TV viewing. We therefore discuss the issue of doping and a new procedure to deal with doping in section 3

HSPG-Binding Peptide Corresponding to the Exon 6a-Encoded Domain of VEGF Inhibits Tumor Growth by Blocking Angiogenesis in Murine Model

Vascular endothelial growth factor VEGF165 is a critical element for development of the vascular system in physiological and pathological angiogenesis. VEGF isoforms have different affinities for heparan sulphate proteoglycan (HSPG) as well as for VEGF receptors; HSPGs are important regulators in vascular development. Therefore, inhibition of interactions between VEGF and HSPGs may prevent angiogenesis. Here, we demonstrate that an HSPG-binding synthetic peptide, corresponding to exon 6a-encoded domain of VEGF gene, has anti-angiogenic property. This 20 amino acids synthetic peptide prevents VEGF165 binding to several different cell types, mouse embryonic sections and inhibits endothelial cell migration, despite its absence in VEGF165 sequence. Our in vivo anti-tumor studies show that the peptide inhibits tumor growth in both mouse Lewis-Lung Carcinoma and human Liposarcoma tumor-bearing animal models. This is the first evidence that a synthetic VEGF fragment corresponding to exon 6a has functional antagonism both in vitro and in vivo. We conclude that the above HPSG binding peptide (6a-P) is a potent inhibitor of angiogenesis-dependent diseases

Differential Effects of Attention-, Compassion-, and Socio-Cognitively Based Mental Practices on Self-Reports of Mindfulness and Compassion

Research on the effects of mindfulness- and compassion-based interventions is flourishing along with self-report scales to assess facets of these broad concepts. However, debates remain as to which mental practices are most appropriate to develop the attentional, cognitive, and socio-affective facets of mindfulness and compassion. One crucial question is whether present-moment, attention-focused mindfulness practices are sufficient to induce a cascade of changes across the different proposed facets of mindfulness, including nonjudgmental acceptance, as well as compassion or whether explicit socio-affective training is required. Here, we address these questions in the context of a 9-month longitudinal study (the ReSource Project) by examining the differential effects of three different 3-month mental training modules on subscales of mindfulness and compassion questionnaires. The “Presence” module, which aimed at cultivating present-moment-focused attention and body awareness, led to increases in the observing, nonreacting, and presence subscales, but not to increases in acceptance or nonjudging. These latter facets benefitted from specific cultivation through the socio-cognitive “Perspective” module and socio-affective, compassion-based “Affect” module, respectively. These modules also led to further increases in scores on the subscales affected by the Presence module. Moreover, scores on the compassion scales were uniquely influenced by the Affect module. Thus, whereas a present-moment attention-focused training, as implemented in many mindfulness-based programs, was indeed able to increase attentional facets of mindfulness, only socio-cognitive and compassion-based practices led to broad changes in ethical-motivational qualities like a nonjudgmental attitude, compassion, and self-compassion