Showing papers on "Urban climate published in 2021"

Global multi-model projections of local urban climates

Abstract: Effective urban planning for climate-driven risks relies on robust climate projections specific to built landscapes. Such projections are absent because of a near-universal lack of urban representation in global-scale Earth system models. Here, we combine climate modelling and data-driven approaches to provide global multi-model projections of urban climates over the twenty-first century. The results demonstrate the inter-model robustness of specific levels of urban warming over certain regions under climate change. Under a high-emissions scenario, cities in the United States, Middle East, northern Central Asia, northeastern China and inland South America and Africa are estimated to experience substantial warming of more than 4 K—larger than regional warming—by the end of the century, with high inter-model confidence. Our findings highlight the critical need for multi-model global projections of local urban climates for climate-sensitive development and support green infrastructure intervention as an effective means of reducing urban heat stress on large scales. An urban climate model emulator has been used with a multi-model archive to estimate that in a high-emissions scenario, many cities will warm by over 4 K during local summers. Near-global relative humidity decreases highlight the potential for green infrastructure and more efficient urban cooling mechanisms.

Urban change as an untapped opportunity for climate adaptation

Abstract: Urban social–ecological–technological systems (SETS) are dynamic and respond to climate pressures. Change involves alterations to land and resource management, social organization, infrastructure, and design. Research often focuses on how climate change impacts urban SETS or on the characteristics of urban SETS that promote climate resilience. Yet passive approaches to urban climate change adaptation may disregard active SETS change by urban residents, planners, and policymakers that could be opportunities for adaptation. Here, we use evidence of urban social, ecological, and technological change to address how SETS change opens windows of opportunity to improve climate change adaptation.

Mapping Local Climate Zones and Their Applications in European Urban Environments: A Systematic Literature Review and Future Development Trends

Abstract: In the light of climate change and burgeoning urbanization, heat loads in urban areas have emerged as serious issues, affecting the well-being of the population and the environment. In response to a pressing need for more standardised and communicable research into urban climate, the concept of local climate zones (LCZs) has been created. This concept aims to define the morphological types of (urban) surface with respect to the formation of local climatic conditions, largely thermal. This systematic review paper analyses studies that have applied the concept of LCZs to European urban areas. The methodology utilized pre-determined keywords and five steps of literature selection. A total of 91 studies were found eligible for analysis. The results show that the concept of LCZs has been increasingly employed and become well established in European urban climate research. Dozens of measurements, satellite observations, and modelling outcomes have demonstrated the characteristic thermal responses of LCZs in European cities. However, a substantial number of the studies have concentrated on the methodological development of the classification process, generating a degree of inconsistency in the delineation of LCZs. Recent trends indicate an increasing prevalence of the accessible remote-sensing based approach over accurate GIS-based methods in the delineation of LCZs. In this context, applications of the concept in fine-scale modelling appear limited. Nevertheless, the concept of the LCZ has proven appropriate and valuable to the provision of metadata for urban stations, (surface) urban heat island analysis, and the assessment of outdoor thermal comfort and heat risk. Any further development of LCZ mapping appears to require a standardised objective approach that may be globally applicable.

Quantifying the response of surface urban heat island to urbanization using the annual temperature cycle model

Abstract: Urban heat island (UHI) plays an important role in urban sustainability under climate change. Urbanization is the driving force of UHI. However, the quantification of UHI's response to urbanization is still challenging due to the lack of robust and continuous temperature and urbanization datasets and reliable quantification methods. This study developed a framework to quantify the response of surface UHI (SUHI) to urban expansion using the annual temperate cycle model. We developed a continuous annual SUHI series at the buffer level from 2003 to 2018 in the Jing-Jin-Ji region of China using MODIS land surface temperature and imperviousness derived from a high-resolution urban map. We then investigated the spatiotemporal dynamic of SUHI under urban expansion and examined the underlying mechanism. Spatially, the largest SUHI interannual variations occurred in suburban areas compared to the urban center and rural areas. Temporally, the increase in SUHI under urban expansion was more significant in daytime compare to nighttime. We found that the seasonal variation of SUHI was largely affected by the seasonal variations of vegetation in rural areas and the interannual variation was mainly attributed to urban expansion in urban areas. Additionally, urban greening led to the decrease in summer daytime SHUI in central urban areas. These findings deepen the understanding of the long-term spatiotemporal dynamic of UHI and the quantitative relationship between UHI and urban expansion, providing a scientific basis for prediction and mitigation of future UHI.

Human behaviour change and its impact on urban climate: Restrictions with the G20 Osaka Summit and COVID-19 outbreak

Abstract: Here we explored human behaviour change impacts on urban climate during the G20 Osaka Summit and the coronavirus 2019 (COVID-19) outbreak. The G20 Summit was held in the Asian megacity of Osaka, Japan on 28–29 June 2019. Due to the G20 restrictions, the traffic count in the city centre was lower by 33% compared with that 1 week prior (the usual week). The urban/office area population was reduced by approximately 10%; however, the residential population increased by 1%. Here we estimate the impact of G20 restrictions on anthropogenic heat (QF) and surface air temperature using a regional climate model coupled with urban canopy and building energy models. The results showed that the daytime QF and air temperature decreased by 15.6 W land-m−2 and 0.05 °C, respectively, in commercial areas of the city. The method described here is expected to be useful for estimating the impacts of similar political events and more extensive stay-at-home restrictions due to the recent COVID-19 pandemic on urban climates. A simple estimation showed that the COVID-19 restrictions resulted in QF of 76.3 W land-m−2 and a 0.13 °C temperature reduction in urban areas, thus, three- to five-fold the impact of the G20 Summit.

Urban climate and resiliency: A synthesis report of state of the art and future research directions

Abstract: The Urban Climate and Resiliency-Science Working Group (i.e., The WG) was convened in the summer of 2018 to explore the scientific grand challenges related to climate resiliency of cities. The WG leveraged the presentations at the 10th International Conference on Urban Climate (ICUC10) held in New York City (NYC) on 6–10 August 2018 as input forum. ICUC10 was a collaboration between the International Association of Urban Climate, American Meteorological Society, and World Meteorological Organization. It attracted more than 600 participants from more than 50 countries, resulting in close to 700 oral and poster presentations under the common theme of “Sustainable & Resilient Urban Environments”. ICUC10 covered topics related to urban climate and weather processes with far-reaching implications to weather forecasting, climate change adaptation, air quality, health, energy, urban planning, and governance. This article provides a synthesis of the analysis of the current state of the art and of the recommendations of the WG for future research along each of the four Grand Challenges in the context of urban climate and weather resiliency; Modeling, Observations, Cyber-Informatics, and Knowledge Transfer & Applications.

Heatwaves and Summer Urban Heat Islands: A Daily Cycle Approach to Unveil the Urban Thermal Signal Changes in Lisbon, Portugal

Abstract: Lisbon is a European Mediterranean city, greatly exposed to heatwaves (HW), according to recent trends and climate change prospects. Considering the Atlantic influence, air temperature observations from Lisbon’s mesoscale network are used to investigate the interactions between background weather and the urban thermal signal (UTS) in summer. Days are classified according to the prevailing regional wind direction, and hourly UTS is compared between HW and non-HW conditions. Northern-wind days predominate, revealing greater maximum air temperatures (up to 40 °C) and greater thermal amplitudes (approximately 10 °C), and account for 37 out of 49 HW days; southern-wind days have milder temperatures, and no HWs occur. Results show that the wind direction groups are significantly different. While southern-wind days have minor UTS variations, northern-wind days have a consistent UTS daily cycle: a diurnal urban cooling island (UCI) (often lower than –1.0 °C), a late afternoon peak urban heat island (UHI) (occasionally surpassing 4.0 °C), and a stable nocturnal UHI (1.5 °C median intensity). UHI/UCI intensities are not significantly different between HW and non-HW conditions, although the synoptic influence is noted. Results indicate that, in Lisbon, the UHI intensity does not increase during HW events, although it is significantly affected by wind. As such, local climate change adaptation strategies must be based on scenarios that account for the synergies between potential changes in regional air temperature and wind.

A systematic review of urban climate research in cold and polar climate regions

Abstract: Cities are at the forefront of the climate change issue and are responsible for about 39% of global carbon dioxide emissions. They can form their own climate which is often characterized by higher temperatures and pollution levels, less wind, and solar access compared to their surroundings. This paper presents a systematic review of publications on cities in cold and polar climate regions as defined by the Koppen-Geiger climate classification to determine the most-researched topics, identify sparsely incorporated research areas, synthesize research evidence and summarize the most important results. In total, 101 papers have been included, categorized, and analyzed according to their publication year, country, climate, topic, method, keywords, citations, and publication channels. The articles were classified into nine main topics: urban heat island (UHI) magnitude, UHI mitigation, other UHI related, biometeorology, air pollution, urban boundary layer and atmospheric boundary layer, time series analysis, other urban meteorological phenomena, and research not falling under the previous eight categories. The most-covered topic was the UHI effect. The outweighing part of studies used on-site measurements for obtaining data, while some studies were dedicated to understanding the structure, or the temporal and spatial variability of the UHI, often by using numerical tools. The review reveals significant gaps in the research of microclimatic characteristics and physical properties of the materials in urban design. Ongoing climate change and the particular vulnerability of cold and polar climate regions makes it especially important to review, develop, and adopt climate adaption and mitigation strategies for sustainable urban development.

Green Roofs and Walls Design Intended to Mitigate Climate Change in Urban Areas across All Continents

Abstract: Green roofs and walls can mitigate the environmental and climate change of a city. They can decrease the urban heat island (UHI), reduce greenhouse gas emissions, fix environmental pollutants, manage urban stormwater runoff, attenuate noise, and enhance biodiversity. This paper aims to analyse green roofs and walls in the possible mitigation of urban climate change and compare it by continent. Green roofs and walls might decrease the air temperature in a city up to 11.3 °C and lower the thermal transmittance into buildings up to 0.27 W/m2 K. Urban greening might sequester up to 375 g C·m−2 per two growing seasons and increase stormwater retention up to 100%. Urban greening might attenuate city noise up to 9.5 dB. The results found green roofs and walls of varied effectiveness in ameliorating climate extremes present in host continents. Results show urban planners might focus on green roofs and walls exposure to attenuate temperatures in hotter Asian cities and advise greening in cities in Africa and Asia. European and American designers might optimise runoff water capacity of green roofs and walls systems and use greening in old buildings to improve insulation. Recommendations are made based on the study to concentrate certain designs to have greater impact on priority climate challenges, whether UHI or stormwater related. This study provides information for decision and policymakers regarding design and exposure of green roofs and walls to mitigate urban environmental and climate change.

An integrated multiscale urban microclimate model for the urban thermal environment

Abstract: An urban microclimate model integrated with the mesoscale, local scale, microscale and building scale models is presented for the urban thermal environment and urban heat island (UHI) mitigation study. This integrated multi-scale and multi-physics urban microclimate model takes the impacts on the urban microclimate of multiple physical processes of regional climate, urban climate, building and pavement material properties, and anthropogenic heat into account. This objective is achieved by coupling weather and energy models, the weather research forecasting (WRF), OpenFOAM and EnergyPlus. This study presents a method of distributing initial and boundary conditions from mesoscale into microscale through the integration of building thermal behaviour and microclimate. We further examine the integrated model by taking the Kent Ridge campus of National University of Singapore (NUS) as a test case. The preliminary application focuses on the assessment of weather conditions at the local scale and the feasibility of using mesoscale WRF outputs as inputs for the CFD model.

Impact of COVID-19-Related Traffic Slowdown on Urban Heat Characteristics

Abstract: Governments around the world have implemented measures to slow down the spread of COVID-19, resulting in a substantial decrease in the usage of motorized transportation The ensuing decrease in the emission of traffic-related heat and pollutants is expected to impact the environment through various pathways, especially near urban areas, where there is a higher concentration of traffic In this study, we perform high-resolution urban climate simulations to assess the direct impact of the decrease in traffic-related heat emissions due to COVID-19 on urban temperature characteristics One simulation spans the January–May 2020 period; two additional simulations spanning the April 2019–May 2020 period, with normal and reduced traffic, are used to assess the impacts throughout the year These simulations are performed for the city of Montreal, the second largest urban centre in Canada The mechanisms and main findings of this study are likely to be applicable to most large urban centres around the globe The results show that an 80% reduction in traffic results in a decrease of up to 1 °C in the near-surface temperature for regions with heavy traffic The magnitude of the temperature decrease varies substantially with the diurnal traffic cycle and also from day to day, being greatest when the near-surface wind speeds are low and there is a temperature inversion in the surface layer This reduction in near-surface temperature is reflected by an up to 20% reduction in hot hours (when temperature exceeds 30 °C) during the warm season, thus reducing heat stress for vulnerable populations No substantial changes occur outside of traffic corridors, indicating that potential reductions in traffic would need to be supplemented by additional measures to reduce urban temperatures and associated heat stress, especially in a warming climate, to ensure human health and well-being

Geospatial analysis of land use driving force in coal mining area: case study in Ningdong, China

Abstract: Geospatial techniques such as remote sensing and Geographic Information System are very important for studying the dynamic process of land use. To analyze the land use change and assess the driving force, SPOT satellite images of 2005, 2010, 2015 and 2018 were used. Classification of land use was applied using Normalized Difference Vegetation Index and Maximum Likelihood Technique in ENVI 5.3. Transition images and matrix were applied using Arcgis10.5 with the Excel PivotTable function. To determine the driving forces of land use change in the study area, Quantitative and Qualitative analysis were applied. Data were compared with statistical analysis using Principal Component Analysis (PCA). Results showed that, the images of the study area were categorized into vegetation (arable land, garden, woodland, grassland, water and agriculture), construction (industrial and transportation) and unutilized land (salt marsh, sandy land, bare land and gully erosion land). From 2005 to 2018, constriction land use greatly increased from 100.41 km2 (2.88%) and 305.13 km2 (8.76%), respectively. Vegetation was decreased from 3190 km2 (91.55%) 3028 km2 (86.91%) in 2005 and 2018, respectively. Results of the comprehensive index of land use degree, dynamic degree, quantitative and qualitative analysis show major changes in land use of the area that caused by human activities especially new developments during the period of the study. The results showed that the Ningdong base in 2005–2018 has been in the stage of sustainable development, mainly in the conversion of grassland, forest land and cultivated land to construction land. High values of rate of change in land use related to the development and new construction and building area. This development might be as a result of anthropogenic activities through urban growth coupled with its potential impacts on urban climate. The principal component analysis shows that human activities drive the change of land use pattern in Ningdong, mainly including the policy of closing the grazing ban, industrialization and scale, population growth and urbanization. Results can provide effective data for the future ecological environment protection and sustainable development of Ningdong Energy Base. Remote sensing is a good technique for assessing the actual sequence in the development of any area that may be caused by human activities.

Integration of a Building Energy Model in an Urban Climate Model and its Application

Abstract: We report the ability of an urban canopy model, coupled with a regional climate model, to simulate energy fluxes, the intra-urban variability of air temperature, urban-heat-island characteristics, indoor temperature variation, as well as anthropogenic heat emissions, in Berlin, Germany. A building energy model is implemented into the Double Canyon Effect Parametrization, which is coupled with the mesoscale climate model COSMO-CLM (COnsortium for Small-scale MOdelling in CLimate Mode) and takes into account heat generation within buildings and calculates the heat transfer between buildings and the urban atmosphere. The enhanced coupled urban model is applied in two simulations of 24-day duration for a winter and a summer period in 2018 in Berlin, using downscaled reanalysis data to a final grid spacing of 1 km. Model results are evaluated with observations of radiative and turbulent energy fluxes, 2-m air temperature, and indoor air temperature. The evaluation indicates that the improved model reproduces the diurnal characteristics of the observed turbulent heat fluxes, and considerably improves the simulated 2-m air temperature and urban heat island in winter, compared with the simulation without the building energy model. Our set-up also estimates the spatio–temporal variation of wintertime energy consumption due to heating with canyon geometry. The potential to save energy due to the urban heat island only becomes evident when comparing a suburban site with an urban site after applying the same grid-cell values for building and street widths. In summer, the model realistically reproduces the indoor air temperature and its temporal variation.

High-Resolution Modelling of Thermal Exposure during a Hot Spell: A Case Study Using PALM-4U in Prague, Czech Republic

Abstract: The modelling of thermal exposure in outdoor urban environments is a highly topical challenge in modern climate research. This paper presents the results derived from a new micrometeorological model that employs an integrated biometeorology module to model Universal Thermal Climate Index (UTCI). This is PALM-4U, which includes an integrated human body-shape parameterization, deployed herein for a pilot domain in Prague, Czech Republic. The results highlight the key role of radiation in the spatiotemporal variability of thermal exposure in moderate-climate urban areas during summer days in terms of the way in which this directly affects thermal comfort through radiant temperature and indirectly through the complexity of turbulence in street canyons. The model simulations suggest that the highest thermal exposure may be expected within street canyons near the irradiated north sides of east–west streets and near streets oriented north–south. Heat exposure in streets increases in proximity to buildings with reflective paints. The lowest heat exposure during the day may be anticipated in tree-shaded courtyards. The cooling effect of trees may range from 4 °C to 9 °C in UTCI, and the cooling effect of grass in comparison with artificial paved surfaces in open public places may be from 2 °C to 5 °C UTCI. In general terms, this study illustrates that the PALM modelling system provides a new perspective on the spatiotemporal differentiation of thermal exposure at the pedestrian level; it may therefore contribute to more climate-sensitive urban planning.