Urban heat island and inertial effects : analyse from field data to spatial analysis

International audienceThe maximum urban heat island often occurs few hours after sunset. This may be explained by the thermal inertia of the urban canopy which is often much higher than that of rural sites. The cooling rate is an indicator of urban thermal inertia computed from on-site measurement but is mainly used to dissociate thermal behaviour difference between urban and rural sites. This paper proposes a new method to better dissociate the thermal inertia properties between urban sites from air temperature measurement.The first part of our paper presents the method of computation, its results under different meteorological conditions which are then compared to the results obtained from the cooling rate calculation. Our method is based on the phase shift computation of temperature diurnal cycles between several urban stations and a reference rural station. Fifteen minutes data collected during four years from ten temperature stations are used. The stations network is located in Nantes, the 6th largest city of France with a total population in its metropolitan area of 590 000 inhabitants. The climate is western European oceanic and is characterized by a relatively mild summer. The phase shift was first calculated considering different meteorological situations. The results show that the sun radiation amount affects directly the phase shift difference values. The wind speed and direction also play a role on the results even if the influence is lower. In a second step, our indicator is compared to the average cooling rate after sunset, an usual indicator of thermal inertia. The results show that the phase shift better dissociates the stations than the cooling rate regarding to their thermal inertia properties.In a second step, the phase shift results are analysed in relation with geographical indicators (facade density, vegetation density, etc.) calculated from BDTopo®. The reference surface for the spatial analysis is defined by concentric circles of different sizes around each measurement station. Results of linear regressions show that our new thermal inertia indicator is well correlated to geographical parameters (R² > 0,5 - e.g. for aspect ratio). These results can be used to identify high thermal inertia zones, where the urban heat island is expected to occur during night-time

Etat de santé des migrants précarisés : l'exemple de l'aide d'urgence dans le Canton de Vaud

En 2008, la PMU et le CHUV ont mis en place une commission chargée d'évaluer, pour le canton de Vaud, les demandes fondées sur des arguments médicaux d'aménagement des conditions d'hébergement de personnes soumises au régime de l'aide d'urgence, introduit à la suite de l'acceptation en votation populaire, le 24 septembre 2006, de la nouvelle loi sur l'asile (LAsi). Nous présentons le contexte historique, politique, institutionnel et médical dans lequel ce groupe de travail intervient, ainsi que ses modalités de fonctionnement, puis abordons les résultats d'une analyse récente de nos données sur les caractéristiques démographiques et l'état de santé des personnes dont les dossiers nous ont été soumis. Cette analyse révèle leur mauvaise santé générale, notamment psychique, avec en particulier une prévalence très élevée d'états de stress post-traumatiques. De façon surprenante, les événements traumatiques surviennent assez fréquemment après l'arrivée en Suisse. Nous évoquons pour conclure une série de préoccupations éthiques en rapport avec cette activité

Reproductive performance of common dentex, Dentex dentex, broodstock held under different photoperiod and constant temperature conditions

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Reproductive performance of common dentex, Dentex dentex, broodstock held under different photoperiod and constant temperature conditions

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Durcissement des lois sociales et santé des migrants forcés: trois ans après (a Loi sur l'asile (LAsi) [Social policy hardening and forced immigrant's health: 3 years after the Asylum Law (LAsi)'s introduction].

In the canton de Vaud, General Practioners (GPs) caring for asylum seekers under the "aide d'urgence" regime can ask for an adaptation of their housing conditions, by filling out a specific form and addressing it to the medical commission responsible for advising the EVAM (the housing institution for asylum seekers) on these issues. The forms addressed to the commission are indicative of a worrisome state of health in this population, especially for mental health. More than 70% report at least one psychiatric diagnosis. Most frequent are anxiety and depressive disorders, as well as many posttraumatic stress disorders, associated with traumatic events both in the country of origin and in Switzerland. Adapting the housing conditions, based on vulnerabilities that the GP has specifically documented, may contribute to improve the health of the most vulnerable asylum seekers

Large-eddy simulation of flow and dispersion in an heterogeneous urban area: comparison with field data

International audienc

Large-eddy simulation of flow and dispersion in an heterogeneous urban area: comparison with field data

International audienc