Some actions intended to adapt to climate change may do more harm than good, especially when they consume energy, making it more difficult to shift to decarbonized energy, or when, in meeting the ...needs of one group of people, they increase the vulnerability of others. Heat wave risk provides a typical example: air conditioning (AC) equipment may trigger large energy consumption and worsen outdoor heat stress. Alternative adaptation strategies exist, but it is not clear whether they can prevent the massive use of AC. Here, with an interdisciplinary modeling platform, taking Paris as a case study, we provide a first quantified analysis of the efficiency of adaptation strategies (large scale urban greening, building insulation policy, and generalized behavioral changes in AC use) in reducing future potential AC need. We find that even ambitious strategies do not appear sufficient to totally replace AC and ensure thermal comfort, under a median climate change scenario. They can, however, reduce AC energy use by half during heat waves and compensate for the heat released to the outdoor environment. Our results show that adaptation actions, implemented early, may play a key role if we are to remain on a low-carbon pathway.
The evolution of the Parisian urban climate under a changing climate is analyzed from long-term offline numerical integrations including a specific urban parameterization. This system is forced by ...meteorological conditions based on present-climate reanalyses (1970–2007), and climate projections (2071–2099) provided by global climate model simulations following two emission scenarios (A1B and A2). This study aims at quantifying the impact of climate change on air temperature within the city and in the surroundings. A systematic increase of 2-meter air temperature is found. In average according to the two scenarios, it reaches + 2.0/2.4°C in winter and + 3.5/5.0°C in summer for the minimum and maximum daily temperatures, respectively. During summer, the warming trend is more pronounced in the surrounding countryside than in Paris and suburbs due to the soil dryness. As a result, a substantial decrease of the strong urban heat islands is noted at nighttime, and numerous events with negative urban heat islands appear at daytime. Finally, a 30% decrease of the heating degree days is quantified in winter between present and future climates. Inversely, the summertime cooling degree days significantly increase in future climate whereas they are negligible in present climate. However, in terms of accumulated degree days, the increase of the demand in cooling remains smaller than the decrease of the demand in heating.
Ecoclimap, a new complete surface parameter global dataset at a 1-km resolution, is presented. It is intended to be used to initialize the soil–vegetation–atmosphere transfer schemes (SVATs) in ...meteorological and climate models (at all horizontal scales). The database supports the “tile” approach, which is utilized by an increasing number of SVATs. Two hundred and fifteen ecosystems representing areas of homogeneous vegetation are derived by combining existing land cover maps and climate maps, in addition to using Advanced Very High Resolution Radiometer (AVHRR) satellite data. Then, all surface parameters are derived for each of these ecosystems using lookup tables with the annual cycle of the leaf area index (LAI) being constrained by the AVHRR information. The resulting LAI is validated against a large amount of in situ ground observations, and it is also compared to LAI derived from the International Satellite Land Surface Climatology Project (ISLSCP-2) database and the Polarization and Directionality of the Earth’s Reflectance (POLDER) satellite. The comparison shows that this new LAI both reproduces values coherent at large scales with other datasets, and includes the high spatial variations owing to the input land cover data at a 1-km resolution. In terms of climate modeling studies, the use of this new database is shown to improve the surface climatology of the ARPEGE climate model.
Urban Climates and Climate Change Masson, Valéry; Lemonsu, Aude; Hidalgo, Julia ...
Annual review of environment and resources,
10/2020, Letnik:
45, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Cities are particularly vulnerable to extreme weather episodes, which are expected to increase with climate change. Cities also influence their own local climate, for example, through the relative ...warming known as the urban heat island (UHI) effect. This review discusses urban climate features (even in complex terrain) and processes. We then present state-of-the-art methodologies on the generalization of a common urban neighborhood classification for UHI studies, as well as recent developments in observation systems and crowdsourcing approaches. We discuss new modeling paradigms pertinent to climate impact studies, with a focus on building energetics and urban vegetation. In combination with regional climate modeling, new methods benefit the variety of climate scenarios and models to provide pertinent information at urban scale. Finally, this article presents how recent research in urban climatology contributes to the global agenda on cities and climate change.
Coupled atmosphere‐fire modeling is recognized as a relevant approach for the representation of the interaction between a wildland fire and local meteorology at landscape scales. The atmospheric ...model component used in the coupled system is based on several approximations, which are adopted for computational efficiency or physical processes representation, including the widely used anelastic approximation. The validity domain of the anelastic approximation may be questioned in the context of high‐resolution wildland fire modeling due to the large fire‐induced heat releases near the surface. This study aims to study this question with the MesoNH anelastic model coupled with the Blaze fire model. A compressible version of the MesoNH‐Blaze coupled model has been developed for comparison with the anelastic system. The FireFlux I experimental fire is used for this comparative study conducted at a 10‐m and a 25‐m horizontal atmospheric resolution. Results show significant anelastic/compressible differences at a 10‐m resolution on the physical processes occurring near the fire with higher horizontal velocities and the presence of gravity waves downstream of the fire. This is in addition to the fire plume with realistic larger vertical velocities. Differences at a 25‐m resolution are much smaller in all evaluated processes. The compressible system only enriches the physics underlying fire‐atmosphere interactions at a very high resolution, which means that the anelastic approximation remains relevant for large‐scale coupled atmosphere‐fire simulations, considering the significant economy concerning numerical costs.
Plain Language Summary
Wildfires burn large amounts of forests each year, destroying the living habitat of many species, endangering human settlements and provoking cross‐continent smoke events leading to air quality issues. Wildfires result from complex physical, chemical and biological processes. Understanding the fundamental processes driving wildfire behavior is a key point for the prediction of fire spread across the landscape and the induced atmospheric dynamics. Numerical models coupling the atmospheric dynamics (wind, temperature, air density and pressure, etc.) and fire front evolution are efficient tools in this scientific process. This paper evaluates how such model simulations are affected by the way in which the effects of high air density gradients induced by the very large amount of heat released into the atmosphere are modeled. When the spatial resolution of the atmospheric model is as high as 10 m, an exact – compressible – formulation leads to the formation of gravity waves downstream of the fire, and to stronger fire‐induced wind, fire propagation and larger vertical velocities than an approximate (and computationally faster) approach. At a resolution of 25 m, which is still very high, the approximate approach leads to results, which are as good as the exact one. This can then be used to simulate wildland fire behavior at landscape‐to‐meteorological scales. It also paves the way for future accurate wildfire forecast systems.
Key Points
A compressible version of the MesoNH atmospheric model has been developed to evaluate equation system approximations in wildfire simulation
Horizontally buoyancy‐driven effects induce turbulent movements, waves ahead of the fire, and a bending of the plume
The anelastic approximation for the atmosphere model is suitable to represent wildland fire effects, except for resolutions of 10 m or finer
Snow accumulation in alpine terrain is controlled by three main processes that act at different spatial scales: (i) orographic snowfall, (ii) preferential deposition of snowfall, and (iii) ...wind‐induced snow transport of deposited snow. The relative importance of these processes largely remains uncertain at small scale (10–100 m). This study presents how high‐resolution coupled snowpack/atmosphere simulations help quantifying the effects of these processes. The simulation system consists of the detailed snowpack model Crocus and the atmospheric model Meso‐NH used in Large Eddy Simulation mode. Dedicated routines allow the coupled system to explicitly simulate wind‐induced snow transport. Our case study is a snowfall event that occurred in February 2011 in the French Alps. Three nested domains at 450, 150 and 50 m grid spacing allow the model to simulate the complex 3D precipitation and wind fields down to fine scale. We firstly assess the ability of the coupled model to reproduce meteorological conditions during the event (wind speed and direction, snowfall amount, and blowing snow fluxes). The spatial variability of snowfall and snow accumulation is then considered. At 50 m grid spacing, snowfall presents local maxima associated with the formation of rimed snow aggregates and graupel in regions of sustained updrafts. Variograms show that the resultant spatial variability of snowfall is lower than the variability of snow accumulation when considering snow transport. Despite an overestimation of simulated blowing fluxes, our results suggest that wind‐induced snow transport is the main source of spatial variability of snow accumulation in our case study.
Key Points
Snow accumulation is simulated with a fully coupled snowpack/atmosphere model
Riming influences small‐scale snowfall pattern in alpine terrain
Wind‐induced snow transport is the main source of spatial variability
Turbulence is well represented by atmospheric models at very fine grid sizes, from 10 to 100 m, for which turbulent movements are mainly resolved, and by atmospheric models with grid sizes greater ...than 2 km, for which those movements are entirely parameterized. But what happens at intermediate scales, Wyngaard's so-called terra incognita? Here an original method is presented that provides a new diagnostic by calculating the subgrid and resolved parts of five variables at different scales: turbulent kinetic energy (TKE), heat and moisture fluxes, and potential temperature and mixing ratio variances. They are established at intermediate scales for dry and cumulus-topped convective boundary layers. The similarity theorem allows the determination of the dimensionless variables of the problem. When the subgrid and resolved parts are studied, a new dimensionless variable, the dimensionless mesh size , needs to be added to the Deardorff free convective scaling variables, where h is the boundary layer height and h sub(c) is the height of the cloud layer. Similarity functions for the subgrid and resolved parts are assumed to be the product of the similarity function of the total (subgrid plus resolved) variables and a "partial" similarity function that depends only on . In order to determine the partial similarity function form, large-eddy simulations (LES) of five dry and cloudy convective boundary layers are used. The resolved and subgrid parts of the variables at coarser grid sizes are then deduced from the LES fields. The evolution of the subgrid and resolved parts in the boundary layer with is as follows: fine grids mainly resolve variables. As the mesh becomes coarser, more eddies are subgrid. Finally, for very large meshes, turbulence is entirely subgrid. A scale therefore exists for which the subgrid and resolved parts are equal. This is obtained for in the case of TKE, 0.4 for the potential temperature variance, and 0.8 for the mixing ratio variance, indicating that the velocity structures are smaller than those for the potential temperature, which are smaller than those for the mixing ratio. Furthermore, boundary layers capped by convective clouds have structures larger than dry boundary layer ones as displayed by the scaling in the partial similarity functions. This new diagnostic gives a reference for evaluating current and future parameterizations at kilometric scales. As an illustration, the parameterizations of a mesoscale model are eventually evaluated at intermediate scales. In its standard version, the model produces too many resolved movements, as the turbulence scheme does not sufficiently represent the impact of the subgrid thermal. This is not true when a mass-flux scheme is introduced. However in this case, a completely subgrid thermal is modeled leading to an overestimation of the subgrid part.
This article provides insights into the development of climate services in Toulouse, France, based on an automated weather station network for microclimatic applications, such as urban heat island ...monitoring. Climate services are often thought of as a unique and complete entity that can be built by providers/sellers for users/buyers using different methods and degrees of involvement and participation. In this paper, the the local authority and its technical departments, helped by the national meteorological agency and researchers, were in charge of both providing and using the climate services. Each component, from network deployment to data production and their operational application, was directed by the local authority. Providers, users, products, and solutions were built from the ground up and developed over the last 5 years using the methodology of action research. This article discusses the possibility of understanding climate services by decomposing them into smaller components organized according to the disciplines, abilities, and challenges of each component to easily identify which actors in the local authority administrative organization can most effectively address them. Each component of the climate services based on a weather station network is discussed. This paper also describes how the governance and organization of climate services are built using action research. Co-construction processes with multiple actors encompassing multi-component projects, such as climate services, mobilize multiple disciplinary fields and require project management and organization. This article shows how the different components of the climate services in Toulouse have been integrated into different urban departments taking into consideration their competencies and their associated disciplinary fields with the goal of providing reproducible methods than can be applied elsewhere. The results indicate the real interest of urban departments in climate services. Some departments assumed responsibility for entire parts of the climate services. Their involvement reveals the complexity of truly integrating climate services as a transdisciplinary department into a public structure, in this case, the local authority. Managing the involvement and participation of all the stakeholders of the climate services implies organizing them using a governing body, even if they belong to the same organization or structure.
The Advanced Regional Prediction System (ARPS) is coupled with the tropical town energy budget (tTEB) scheme to analyze the effects of the urban canopy circulation over the metropolitan area of São ...Paulo and its interactions with the sea breeze and mountain-valley circulation in the eastern state of São Paulo, Brazil. Two experiments are carried out for the typical sea-breeze event occurring on 22 August 2014 under weak synoptic forcing and clear-sky conditions: (a) a control run with the default semi-desert surface parametrization and; (b) a tTEB run for the urban canopy of São Paulo. A realistic land-use database over the south-eastern domain of Brazil is used in the downscaling simulation to a horizontal grid resolution of 3 km. Our results indicate that ARPS effectively simulates features of the nighttime and early morning land-breeze circulation, which is affected by the surrounding hills and the nocturnal heat island of São Paulo. By early afternoon, the south-eastern sea-breeze circulation moves inland perpendicular to the upslope of the Serra do Mar scarp, which generates a line of moisture convergence and updrafts further inland. Later, the convergence line reaches São Paulo and interacts with the circulation arising from the urban heat island (UHI), which increases the moisture convergence and strength of updrafts. The surface energy balance indicates that the UHI is caused by large sensible heat storage within the urban canopy during the day, which is later released in the afternoon and at night. The simulations are verified with available radiosonde and surface weather station data, land-surface-temperature estimates from the moderate resolution imaging spectroradiometer, as well as the National Center for Atmospheric Research reanalysis databases. The three-dimensional geometry of the urban canyons within the tTEB scheme consistently improves the thermodynamically-induced circulation over São Paulo.
Urban microclimate studies could help manage heatwave crises and improve climate friendly urban planning. This paper presents adjustments to tools and approaches, in particular the Urban Climate Maps ...framework, typically produced in industrialized countries for contexts relevant to developing countries, where accurate urban data are often not available. In this study, relevant urban, architectural and land use data were collected and constructed to enable numerical simulations of a heat wave episode in the Greater Metropolitan area of Tunis. The simulation results indicate that the diurnal heat stress reached very high values corresponding to an extreme heat stress level, according to the Urban Thermal Climate Index (UTCI) scale, by 9 a.m. local time. The highest sea-breeze speeds were over the sea (∼8 m s−1). However, the effect of the sea breeze was low over densely urbanized areas (<3 m s−1). At night, the intensity of the urban heat island reached +4.5°C. Urban climatic maps were produced via a statistical analysis of the numerical simulation outputs for the diurnal heat stress and the urban heat island intensity. The impact of the sea breeze on the heat stress level is communicated using two UTCI maps. Strategic maps were also proposed to highlight critical areas for urban actors. These strategic maps illustrate the zoning of relevant territorial issues to facilitate dialog with the Urban Planning Agency of the Greater Metropolitan area of Tunis.
PDF
