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Urban overheating is the most documented phenomenon of climate change impacting humans. This article presents the most recent developments on the magnitude and characteristics of urban overheating and the potential synergies with global climatic change. It analyses the latest qualitative and quantitative data on the impact of higher urban temperatures on buildings' energy supply and demand, heat-related mortality, morbidity and wellbeing, human productivity, survivability of low-income populations, and environmental quality of cities. It describes the state of the art on the development of innovative mitigation materials, advanced urban greenery, heat dissipation, and evaporative techniques as the main mitigation and adaptation technologies to offset the impact of urban overheating. It also analyses the current knowledge on the impact of each mitigation technology on energy, health, environmental quality, urban economy, and survivability. Finally, this article presents the main future challenges related to urban overheating and proposes a specific research agenda to alleviate and counterbalance its impact on human life. [ABSTRACT FROM AUTHOR]

Urban overheating, driven by global climate change and urban development, is a major contemporary challenge that substantially impacts urban livability and sustainability. Overheating represents a multifaceted threat to the well‐being, performance, and health of individuals as well as the energy efficiency and economy of cities, and it is influenced by complex interactions between building, city, and global scale climates. In recent decades, extensive discipline‐specific research has characterized urban heat and assessed its implications on human life, including ongoing efforts to bridge neighboring disciplines. The research horizon now encompasses complex problems involving a wide range of disciplines, and therefore comprehensive and integrated assessments are needed that address such interdisciplinarity. Here, our objective is to go beyond a review of existing literature and instead provide a broad overview and integrated assessments of urban overheating, defining holistic pathways for addressing the impacts on human life. We (a) detail the characterization of heat hazards and exposure across different scales and in various disciplines, (b) identify individual sensitivities to urban overheating that increase vulnerability and cause adverse impacts in different populations, (c) elaborate on adaptive capacities that individuals and cities can adopt, (d) document the impacts of urban overheating on health and energy, and (e) discuss frontiers of theoretical and applied urban climatology, built environment design, and governance toward reduction of heat exposure and vulnerability at various scales. The most critical challenges in future research and application are identified, targeting both the gaps and the need for greater integration in overheating assessments. Plain Language Summary: Many major cities are faced with the compounding effects of climate change and rapid urbanization. One of the main challenges that result is urban overheating, which leads to negative impacts on human life (deteriorating health, productivity, and well‐being) and urban energy systems. Heat exposure in cities, however, is only the trigger and there are other factors that influence impacts. Urban heat vulnerability exists when sensitive people and infrastructure are exposed to extreme heat, and negative impacts ensue if there is a lack of capacity to respond and adapt. Accordingly, to combat overheating challenges, it is critical that multidisciplinary solutions are integrated to mitigate exposure, reduce sensitivity, and increase adaptive capacities. This paper provides an integrated assessment of urban overheating literature, defining pathways for addressing the impacts on human life. We review the state‐of‐the‐art methods used to quantify heat hazards and exposure, detail the sensitivity of people and infrastructure to overheating, and elaborate on the adaptive capacities that individuals and cities can undertake in response. We provide recommendations for both researchers and policymakers that will minimize overheating impacts. These recommendations range from modifications to urban and building design to engaging citizens and informing urban overheating governance. Key Points: Urban overheating is the exceedance of locally‐defined thermal thresholds that lead to negative impacts on people and urban systemsExposure to heat hazards compounded with sensitivity and reduced adaptive capacity of people and urban systems lead to increased risk levelsResearch and application should provide integrated solutions to mitigate exposure, reduce sensitivity, and increase adaptive capacities [ABSTRACT FROM AUTHOR]

Local and global climate change increases the ambient temperature of cities by several degrees with important consequences on energy consumption, health and the economy. Advanced urban mitigation technologies contribute to decrease the ambient temperature and counterbalance the impact of urban heat islands. The present paper analyses and presents in a comparative way the mitigation potential of the known mitigation technologies using performance data from about 220 real scale urban rehabilitation projects. The average and peak temperature drop of reflective technologies, greenery, evaporative systems, earth to air heat exchangers and their combinations is calculated and presented. The mitigation potential of the main systems like cool roofs, cool pavements, green roofs, urban trees, pools and ponds, sprinklers, fountains, and evaporative towers, is analysed. It is found that the potential of the main mitigation technologies is considerable and can counterbalance UHI effects partly or fully. The average peak temperature drop calculated for all projects is close to 2 K, while the corresponding decrease of the average ambient temperature is close to 0.74 K. Almost 31% of the analysed projects resulted in a peak temperature drop below 1 K, 62% below 2 K, 82% below 3 K and 90% below 4 K. [ABSTRACT FROM AUTHOR]

This paper presents results of a study of the impact of future climate change scenarios as developed by the Intergovernmental Panel on Climate Change and implemented in weather files for specific future time slices (2020, 2050 and 2080) for the three climatic regions of Greece on the design of the external envelope of a hotel building in Greece. The impact of climate change on the hotel is assessed via hourly simulations of a calibrated model developed using the software TRNSYS. Additionally, the paper aims to identify optimal refurbishment strategies, given the constraints of the existing case-study building when transposed to the three different climatic zones in Greece. Two modes of the hotel building were studied: ‘all year’ and ‘seasonally’ operated. It was found that different external envelope energy-efficient strategies can be applied depending on the climatic zone and whether the hotel is all-year or seasonally operated. [ABSTRACT FROM AUTHOR]

Urban heat island is the more documented phenomenon of climate change. Information on the magnitude and the characteristics of the canopy layer urban heat island measured in 101 cities and regions of Asia and Australia and collected through 88 scientific articles, are compiled, evaluated and presented. Data are classified in several clusters according to the experimental protocol used and the type of statistical information reported regarding the magnitude of the urban heat island. Results and detailed analysis are given for each defined cluster. Very significant differences on the UHI intensity are found between the clusters and analyzed in detail. The detailed impact of the main weather parameters and conditions on the magnitude of the UHI is also investigated. The specific influence of anthropogenic thermal fluxes as well as of the urban morphological and construction characteristics to UHI is thoroughly examined. The relation between the UHI intensity and the city size is assessed and global relationships of UHI as a function of the urban population are proposed. The seasonal and diurnal variability of the UHI is analyzed and discussed while specific features and conditions like the urban heat island characteristics in coastal cities and the existence of daytime cool islands are explored. Finally, the impact of the selected reference station and its characteristics is considered. [ABSTRACT FROM AUTHOR]

Urban heat island and global warming increase ambient temperature and modify the energy budget of buildings. The magnitude of the modification has been evaluated in a large number of articles, under different climatic and building boundary conditions. This paper collects, analyzes and classifies existing knowledge regarding the energy impact of urban heating to buildings and calculates preliminary indicators and impact figures. Based on the analysis of the impact studies, it is found that in average the cooling load of typical urban buildings is by 13% higher compared to similar buildings in rural areas. Four specific energy impact indicators, the global energy penalty per m 2 , the global energy penalty per m 2 and degree of UHI, the global energy penalty per person and the global energy penalty per person and per degree of the UHI are defined and calculated. The variability of the heating and cooling loads of typical buildings is evaluated for the period 1970–2010. The average increase of the cooling demand is 23% while the corresponding average reduction of the heating is 19%. In total, the average energy consumption of typical buildings for heating and cooling purposes increased by 11% for the same period. [ABSTRACT FROM AUTHOR]

Integrating sustainability in urban design is a prerequisite for adequately addressing the urban challenges related to climate change, resource availability, environmental degradation and energy consumption. For the integration to be well formulated, urban planners need comprehensive microclimatic information at adequate spatial and temporal scales so as to define the bioclimatic design targets of the urban area concerned. In this study a medium size city (Acharnes, built at the southern foothills of Mt Parnitha, at a distance of 10km north of Athens) is examined in terms of its thermal characteristics and the resulting thermal comfort conditions in municipal open spaces. Results show significant thermal loads for specific city areas as well as use of materials which result in adverse thermal conditions and in poor thermal comfort. On the basis of the results, specific guidelines are defined for the sustainable urbanisation of the city of Acharnes, in particular for an urban regeneration project concentrated at the centre of the city. The approach reflects a pattern which may be well applied in cities of respective size and urban characteristics and in similar climatic zones. [ABSTRACT FROM AUTHOR]

Highlights: [•] Very low indoor temperatures in low and very low income housing in Athens Greece. [•] Very low energy consumption because of the energy crisis. [•] Important environmental social and health problems associated to low indoor temperatures. [ABSTRACT FROM AUTHOR]

Abstract: This research focuses on projecting the energy demand of the building sector in Greece by calculating energy consumption, using output data from regional climate models up to 2100. More specifically, Greece was subdivided into 13 climatic zones after assessing climate model data taking into account climate change estimates for the period 2010–2100. These zones allow a detailed estimation of the effects of climate change in specific regions of the country, thus creating a database which is used to model the energy demand of the building sector in each zone. Through the use of building data from Eurostat and the European Centre for Environment, a set of three building typologies was created in relation to the building envelope, which corresponds to 85% of the building stock in Greece. These typologies were later appended to each of the 13 climatic zones and a simulation for their energy demand was calculated using climatic data from 3 distinct climatic scenarios. Results show that the energy demand for heating the building sector in Greece could decrease by about 50%, while the respective energy demand for cooling could increase by as much as 248% until 2100. These effects are more evident in the Southern part of the country. [Copyright &y& Elsevier]

Abstract: Climatic change and heat island effect in combination with the non-proper design of buildings have increased substantially the cooling load of buildings. Night ventilation appears to be one of the more promising passive cooling techniques. Many important theoretical and experimental studies have been performed however the existing information is presented in a segmented way. The present paper analyses energy data from two hundred fourteen air conditioned residential buildings using night ventilation techniques. The specific absolute energy contribution of night ventilation has been calculated. The relation of the cooling demand of the buildings with the specific contribution of night ventilation has been investigated. It is found that the higher the cooling demand of the building, the higher the potential contribution of night ventilation under specific boundary conditions. The role of air flow rate is investigated as well. It is found that the global utilisability of the energy stored during the night increases as a function of the air flow rate and the tilt of the regression line between the energy contribution and the air flow rate increases significantly with the air flow rate applied, although the energy contribution per unit of air flow is decreasing. The whole analysis contributes towards a better understanding and evaluation of the expected energy contribution of night cooling techniques. [Copyright &y& Elsevier]

• Urban Overheating affects energy generation and demand, pollution, health and vulnerability. • It increases the energy demand for cooling and decreases the efficiency of power plants. • Rises the concentration of ground level ozone. • Increase indoor temperature in low income housing. • Increases heat related mortality and morbidity. Urban overheating is documented for more than 400 major cities in the world. Numerous experimental data show that the magnitude of the average temperature increase may exceed 4-5 C, while at the peak may exceed 10 C. Increased ambient temperatures cause a serious impact on the cooling energy consumption, peak electricity demand, heat related mortality and morbidity, urban environmental quality, local vulnerability and comfort. Synergies between urban heat island and heat waves increase further the amplitude of urban overheating The present paper reviews and reports the recent progress and knowledge on the specific impact of current and projected urban overheating in energy, peak electricity demand, air quality, mortality and morbidity and urban vulnerability. In parallel, it discusses new findings related to the characteristics and the magnitude of urban overheating, and reports and analyse the recent knowledge on the synergies between urban heat island and heat waves. [ABSTRACT FROM AUTHOR]

Abstract: This work developed a methodology and an associated calculation platform in order to identify the economic efficient design solutions for residential Net Zero Energy Building (NZEB) design considering the influence of the local climate, the endogenous energy resources and the local economic conditions. One case study of a detached house for 3 climates was analyzed with the tool developed in order to gain insights on the economic space of NZEB solutions and the influence of the climatic context. A methodology for assisting the choice of economically efficient NZEB solutions from the early design stage is now available. Its use in practice may be of great relevance as the results showed that the differences between an economically efficient and economically inefficient NZEB can be over three times both in terms of initial and life cycle cost. [Copyright &y& Elsevier]

Abstract: In the field of energy savings in buildings, the interest towards the school sector is deeply motivated: schools have standard energy demands and high levels of environmental comforts should be guaranteed. The University of Athens in collaboration with the School Authority of Greece undertook a complete program on energy classification and environmental quality of school buildings. Data on energy consumptions were gathered and analysed with the participation of 1100 schools from all the prefectures of Greece. The data have been provided by the school authority of the country (OSK), in collaboration with the management of each school building. With regards to the size of the building and the external climate variability (HDD-method) energy normalization techniques have been applied in order to homogenize the data set. An energy classification tool has been created through clustering techniques, using the collected data regarding the heating energy consumption and as a result five energy classes have been defined. To evaluate the potential energy conservation for each class, the typical characteristics of school buildings belonging to an energy class have to be identified. A new methodology based on the use of the principal components analysis (PCA) has been developed. The method allows to define in an accurate way the typical building of each energy class and thus to perform analysis on the potential energy savings for the specific group of school buildings. By reducing the dimensionality of the problem, a bi-dimensional graphic in the first two PCs coordinate system promotes the understanding of the correlation between the examined variables, as well as the determination of sub-groups of school buildings with similar characteristics. The typical school of seven variables sample is defined as the closest to the medians in the principal components’ coordinate system. [Copyright &y& Elsevier]

Abstract: Commonly used materials in the construction of the building façades located in warm climates, often entrap a great amount of heat from the incoming solar radiation, leading to a respective thermal increase in the interior. The aim of the present study is to examine mineral-based coatings as a passive solar technique that contributes to buildings’ energy efficiency. A series of mineral based samples are developed and tested. Their thermal performance is estimated by infrared thermography and surface temperature measurements. Their optical properties are also measured while the energy efficiency is quantified using simulation techniques. The results revealed that renders based on hydraulic and/or hydrated lime with additions of calcium carbonate powder, as well as mineral paints comprised either of lime wash or silicate minerals can behave as cool coatings and contribute to a significant reduction of the cooling demand in warm climates. [Copyright &y& Elsevier]