Benefits of explicit urban parameterization in regional climate modeling to study climate and city interactions

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.

A surface modelling approach for attribution and disentanglement of the effects of global warming from urbanization in temperature extremes: application to Lisbon

“…[16,[33][34][35][36][37]). Furthermore, the SURFEX-TEB framework is convenient because it has been coupled to widely used RCM and GCM models, and thus it may be employed for operational and research applications in weather and climate [24].…”

“…Additionally, large ensembles of climate simulations obtained by Regional Climate Models (RCMs) are just starting to be used at such high-resolutions (∼3 km) for long climate projections [22,23], but these simulations are still extremely demanding computationally, and the use of appropriate coupled urban canopy models is still non-standard (e.g. [24]).…”

Urban Areas and Urban–Rural Contrasts under Climate Change: What Does the EURO-CORDEX Ensemble Tell Us?—Investigating near Surface Humidity in Berlin and Its Surroundings

“…The Coordinated Regional Climate Downscaling Experiment (CORDEX) offers a state-of-the-art global framework for regional climate model (RCM) simulations and brings together around 30 regional climate modeling groups from across the globe [7][8][9]. Presently, only a limited sub-set of RCMs have developed a more complex representation of urban structures for their models and have conducted explicit studies on urban areas [10][11][12]. Due to limited available computing power, most of the detailed urban model projections with higher spatial resolutions (100 m -3 km grid size) simulate short time ranges, from a few days to a few years, and only focus on a sub-set of climatological variables.…”

Between progress and obstacles in urban climate interdisciplinary studies and knowledge transfer to society

“…Lemonsu et al . and Daniel et al . have studied the impact of urban expansion scenarios on UTCI for future heat‐wave conditions over the Paris region.…”

“…Kusaka et al 50 and Argüeso et al 51 have investigated the evolution of comfort conditions in the future using the WBGT index, based on regional climate simulation with the weather research and forecasting model in Japanese cities and the Sydney region, respectively. Lemonsu et al 37 and Daniel et al 52 have studied the impact of urban expansion scenarios on UTCI for future heat-wave conditions over the Paris region. It is, however, difficult to decide which index to use, as well as how to analyze these indices to assess the impacts on the population in a standardized manner and provide relevant urban climate services for society and users.…”