Abstract
Most climate models do not explicitly model urban areas and at best describe them as rock covers. Nonetheless, the very high resolutions reached now by the regional climate models may justify and require a more realistic parameterization of surface exchanges between urban canopy and atmosphere. To quantify the potential impact of urbanization on the regional climate, and evaluate the benefits of a detailed urban canopy model compared with a simpler approach, a sensitivity study was carried out over France at a 12-km horizontal resolution with the ALADIN-Climate regional model for 1980–2009 time period. Different descriptions of land use and urban modeling were compared, corresponding to an explicit modeling of cities with the urban canopy model TEB, a conventional and simpler approach representing urban areas as rocks, and a vegetated experiment for which cities are replaced by natural covers. A general evaluation of ALADIN-Climate was first done, that showed an overestimation of the incoming solar radiation but satisfying results in terms of precipitation and near-surface temperatures. The sensitivity analysis then highlighted that urban areas had a significant impact on modeled near-surface temperature. A further analysis on a few large French cities indicated that over the 30 years of simulation they all induced a warming effect both at daytime and nighttime with values up to + 1.5 °C for the city of Paris. The urban model also led to a regional warming extending beyond the urban areas boundaries. Finally, the comparison to temperature observations available for Paris area highlighted that the detailed urban canopy model improved the modeling of the urban heat island compared with a simpler approach.
Highlights
General circulation models (GCMs) are implemented at the global scale (Cubasch et al 1992) to simulate and investigate long-term climatic evolutions
Using TEB increases air temperature, which leads to a better representation of the nocturnal and diurnal urban heat islands. Inspired by these works and those of McCarthy et al (2012), the present study focuses on a regional climate modeling framework, by running ALADIN-Climate regional climate models (RCMs) over France with a 12-km spatial resolution and for a longterm simulation of 30 years
These biases are within the range of model from the Euro-CORDEX project and the works of Prein et al (2015), that computed for different RCMs the mean biases over the France domain
Summary
General circulation models (GCMs) are implemented at the global scale (Cubasch et al 1992) to simulate and investigate long-term climatic evolutions. Surface characteristics of urban areas (imperviousness, thermal properties, three-dimensional geometry) alter radiative, energetic, turbulent, and hydrologic processes. They generate a specific local climate, especially positive anomalies in air temperature in the city compared to surrounding areas called urban heat island (UHI, Oke 1982). These urban effects interact with atmospheric boundary layer and local meteorology. Based on observational time series over the second half of the twentieth century, warming effect due to urbanization were already observed at the regional scale in the United States (Stone 2007) and in China (Hua et al 2008; Jones et al 2008).
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