6533b827fe1ef96bd12876aa

RESEARCH PRODUCT

The Urban Heat Island of a middle-size French city as seen by high-resolution numerical experiments and in situ measurements the case of Dijon, Burgundy

subject

description

International audience; This work aims at characterizing the spatio-temporal variability and features of the urban heat island (UHI) over the agglomeration of Dijon (north-eastern France; 260,000 inhabitants) under present-day conditions and during the boreal summer season (June through September). To that end, two complementary approaches are used: • in situ measurements, using a network of 50 Hobo proV2 sensors measuring air temperature and specific humidity every 20 minutes, and implemented since June 2014 throughout the agglomeration; • high-resolution (150m horizontal resolution) meso-scale atmospheric simulations performed using the WRF/ARW model coupled with the BEP-BEM urban canopy model. Special attention was paid to the location of the thermometers. The sites were chosen to ensure a correct sampling of the various urban thermal environments such as described by the classification of Oke (2006). In order to ensure a representativeness of the neighbourhood and not merely the close environment, open locations are preferred, limiting shadows from the vegetation and nearby buildings. The sensors are fixed 3m above the ground surface, over the south face of public lampposts, with specific fixations designed to separate the measurements from the lampposts themselves. The density of our network enables us regionalizing in detail air temperature and humidity over the whole city. Similar attention was also given to the static surface datasets used as surface boundary conditions for the climate modelling system (land-use maps, topography, urban morphology). Public and/or open databases developed by various French and European governmental services (Corine Land Cover, IGN, INSEE and OpenStreetMap databases) were used in order to obtain a generic and reproducible methodology, that can be used for any French city. This presentation is the opportunity to first present the comparisons between both approaches and therefore quantify the capability of the climate modelling system (WRF/ARW - BEP+BEM) to simulate the main features of the UHI in Dijon during the 2014 summer period.