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- Decoding the urban climate of a warming coastal Mediterranean city : the influence of blue and green spaces on human thermal stressPublication . Reis, Cláudia; Lopes, António Manuel Saraiva; Nouri, André Naghi Lopes dos SantosToday, urban areas face severe sustainability and environmental challenges. The urbanization process transforms natural landscapes into efficient radiation-absorbing surfaces, creating heated and thermally uncomfortable atmospheres. The direct outcome of this process is the Urban Heat Island (UHI) effect, which is exacerbated by the ongoing climate changes, characterized by rising air temperatures and more frequent, intense and prolonged heatwave events. This theses explores the potential of using urban vegetation and promoting urban designs that allow local wind systems to naturally ventilate the cities, such as sea and estuarine breezes, as effective heat mitigation strategies. Through a multi scale and multi-source data approach, this investigation aims at quantifying the impact of these blue and green spaces on thermo-physiological comfort during summer on a Southern European coastal city, Lisbon. Firstly, a local weather types classification was generated to summarize the various local meteorological conditions within this city. Subsequently, the Urban Heat Island (UHI) effect was analyzed by local weather types using an European urban climate dataset from the Copernicus Climate Change Service. This analysis aimed to identify critical heating hotspots and the meteorological conditions that contribute to higher UHI magnitudes. Then, the cooling potential of breezes coming from the Tagus river and the Atlantic Ocean was assessed on the thermal summer of 2022 using a large meteorological network installed across Lisbon and GRAMM-SCI mesoscale model. Additionally, the influence densely tree-covered areas (Local Climate Zone - LCZ A) and street trees on outdoor human thermo-physiological comfort during a particular local weather type (very hot summer days) was modelled in SkyHelios and confirmed by mobile measurements across several microscale samples according to LCZ 1 to 9, A and B. Finally, future human thermo-physiological comfort conditions on those urban blocks were modeled according to different climate change scenarios (RCP 4.5 and 8.5) and time periods (2041-2070 and 2071-2100) and considering no major future changes in urban morphology and vegetation.
- Evaluating the cooling potential of urban green spaces to tackle urban climate change in LisbonPublication . Reis, Cláudia; Lopes, AntónioThe increase and optimization of urban vegetation has been considered an e ective mitigation measure of an urban heat island (UHI), with positive e ects on human thermal comfort. In this study, the cooling potential of all green spaces in Lisbon was estimated. For that, several mobile measurements of air temperature data were made in a single park (Gulbenkian’s Garden). These measurements were used for the interpolation of air temperature. Furthermore, urban biomass was estimated using remote sensing products, namely Landsat satellite images. Ultimately, a linear regression model was built from the relation between vegetation density and air temperature. Results regarding the estimation of biomass (AGB) in the city of Lisbon were higher in winter than in summer. The urban green spaces cooling potential model showed that for every decrease of 1 C in air temperature between a measuring point and a reference station we need to increase the area covered by vegetation by 50 m2 (planar measure). This methodology can be applied in other urban areas for the quantification of the cooling e ect provided by vegetation in order to improve urban climate thermal conditions and human well-being and, consequently, to mitigate some consequences of future climate change.
- Climate walking: A comparison study of mobile weather stations and their relevance for urban planning, design, human health and well-beingPublication . Silva, Tiago; Ramusga, R.; Matias, Márcia; Amaro, J.; Bonifácio, Ana; Reis, Cláudia; Chokhachian, A.; Lopes, G.; Almeida, A.; Frazão, J.; Vasconcelos, J.; Lopes, António; Morgado, PauloMicroclimate conditions affect the outdoor urban way of life for humans. These conditions directly impact people’s health and well-being, such as access to medical care or a healthy lifestyle. Human thermal comfort is paramount for people’s health, both physical and mental. In this paper, the study compares two microclimate mobile weather stations (MWS) based on a set of users’-based assessment criteria (usability, user-friendliness, sensors) and thermal comfort (UTCI) results accuracy. The comparison was carried out through continuous mobile transect measurements lasting an hour and a half, conducted on two summer days in Lisbon across distinct urban morphological settings. This research was developed to assist future researchers in urban climatology with the design of microscale studies, particularly in relation to equipment selection, performance assessment, and methodological procedures. In terms of performance, we found the RMSE to be 1.3 ◦C for air temperature, 1.6 % for relative humidity, 1.3 m/s for wind speed, and 8.4 W/m2 for solar radiation for MWS 1, and 1.5 ◦C for air temperature, 2.9 % for relative humidity, 1.5 m/s for wind speed, and 11.6 W/m2 for radiation for MWS 2. Both MWS units exhibited a consistent performance, however, MWS 1 demonstrated greater overall accuracy, particularly in the measurement of air temperature, relative humidity, and wind speed. Differences were also observed between the sensors of MWS 1 and MWS 2, as well as in the MWS usability, factors which may be significant depending on the users’ objectives and available resources. Despite this, both MWS units were deemed suitable for deployment in urban environments, with MWS 2 offering a more intuitive user experience. The findings of this study are particularly relevant for those beginning mobile meteorological measurements, as well as for researchers aiming to address urban heat stress and enhance public well-being and thermal comfort through their work. However, the study is limited by its short duration and geographic scope, and further research is needed to expand its applicability to diverse urban settings.
- A eficiência térmica no potencial de arrefecimento de dois espaços verdes em LisboaPublication . Reis, Cláudia Estêvão dos; Lopes, António Manuel SaraivaAtualmente, a mitigação da ilha urbana de calor (IUC) é uma das grandes para a melhoria das condições de habitabilidade da população urbana. No presente trabalho pretendeu-se a determinação do potencial de arrefecimento dos espaços verdes em Lisboa, quantificando o volume de vegetação necessário para a redução de 1ºC na temperatura do ar. Para tal, foram selecionadas algumas áreas amostra: um jardim de média dimensão (Jardim da Fundação Calouste Gulbenkian), um jardim de pequena dimensão (Jardim Fernando Pessa) e duas ruas, uma com vegetação (Avenida Defensores de Chaves) e outra sem vegetação (Rua Actor Isidoro). Em todos os espaços foram recolhidos dados climáticos (instalação de redes meteorológicas urbanas e medições itinerantes) e, posteriormente, interpolaram-se as temperaturas no interior e no exterior de um jardim, de modo a caraterizar o comportamento térmico destes espaços verdes e a sua influência na área construída envolvente. Ao mesmo tempo, estimou-se a biomassa da cidade de Lisboa, a partir de modelos de deteção remota que recorreram ao índice de vegetação NDVI. Com o volume de massa verde, estimou-se a densidade de vegetação que, juntamente com a interpolação das temperaturas, permitiu a construção de um modelo de regressão linear simples de estimação do potencial de arrefecimento dos espaços verdes. Concluiu-se que todos os espaços verdes estudados conseguiram, em algum momento, arrefecer o ambiente térmico envolvente. No entanto, a intensidade das ilhas de frescura (PCI – Park Cool Island) e as distâncias máximas de arrefecimento registaram grande variabilidade espacial e temporal. No Jardim da Gulbenkian registou-se uma intensidade média da PCI de 2,2ºC, em dias com nebulosidade moderada a forte e uma grande variabilidade em termos de velocidade média do vento. O Jardim Fernando Pessa esteve quase sempre mais quente que a sua área envolvente. Os fatores que poderão explicar estas diferenças prendem-se com a dimensão dos espaços verdes e a densidade e o tipo de vegetação presente, tendo-se constatado que o efeito de arrefecimento de jardins compostos maioritariamente por espécies herbáceas como a relva é muito reduzido ou nulo. Quanto às ruas analisadas, concluiu-se que a rua arborizada esteve, em média, 1ºC mais fresca que a rua sem vegetação, tendo as diferenças máximas atingido 3,7ºC. A partir do modelo de regressão linear simples (temperatura do ar vs densidade da vegetação), concluiu-se que para a redução de 0,02ºC na diferença da temperatura entre um ponto de medição e um ponto fixo é necessário um incremento na vegetação de 1m2 (no plano). Em suma, a metodologia utilizada neste estudo é um ponto de partida para a estimação do potencial de arrefecimento de toda a massa verde da cidade de Lisboa, sendo necessário prosseguir esta investigação estudando um maior número de jardins de Lisboa.
- Modeling the influence of summer sea and estuarine breezes on heat stress in Lisbon (Portugal) using GRAMM-SCIPublication . Reis, Cláudia; Oettl, Dietmar; Lopes, António; Nouri, A. Santos; Vasconcelos, JoãoIn this study, the influence of the Tagus river and Atlantic Ocean breezes in a Mediterranean city (Lisbon) on outdoor thermal comfort was analyzed during the thermal summer days. Hourly wind fields were modeled using the GRAMM-SCI software, initialized with ERA5 reanalysis data. The Universal Thermal Climate Index (UTCI) was calculated for 80 weather stations across the city. Additionally, the UTCI anomalies (ΔUTCI) relative to a reference site (the airport weather station) were calculated during breeze and non-breeze events (typically N/NW winds). Results showed that sea breezes can reduce UTCI levels by up to 2,2◦ C during typical breeze days and up to 5,1◦ C during heatwave breeze events. The effect of these breezes on heat stress conditions is felt up to 4 km from the Tagus river, but especially on the areas up to 500 m. However, in 50 % of the cases where no thermal stress was recorded at the airport during breeze events, Lisbon’s riverfront can be more uncomfortable (moderate heat stress) than the northern part of the city (from 2 to 8 km). Additionally, cooling effect of the breezes is only significant enough to cause a transition to a more comfortable UTCI class (especially from very strong to strong heat stress and from strong to moderate heat stress) during heatwaves (strong to very strong heat stress) and on areas up to 1,5 km from the estuary. The promotion of wind corridors is, therefore, crucial to insuring the progression of sea breezes in urban areas and to reduce heat stress.
- Unveiling the Thermo‐Hygrometric Influence of Summer Sea and Estuarine Breezes (SEBs) in Lisbon (Portugal)Publication . Reis, Cláudia; Lopes, António; Nouri, A. Santos; Vasconcelos, JoãoLocal wind, such as sea breezes, play a crucial role in cooling coastal cities. This study presents new insights about the thermo-hygrometric influence of the Tagus and Atlantic Ocean breezes(sea and estuarine breezes [SEBs]) in Lisbon’s urban climate (Portugal). SEB events were identified in the summer of 2022 according to a wind rotation criterion: the interruption of prevailing North and Northwest (Nortada) winds during the morning, the wind shift to Northeast/East/Southeast and, sometimes, to further South/Southwest/West (rotation between 22.6° and 292.5°) and the return of the regional flow at late afternoon. Additionally, air temperature and absolute humidity anomalies (ΔT/Haurb) were calculated according to the distance to the riverfront area. Results show that SEB occurred on 37 (31%) out of 120 days, mainly in July (43%) and August (32%), between, on average, 10:00 AM and 4:00 PM, and average wind speeds of 3.4 m/s. According to the daily thermo-hygrometric cycle, the areas up to 4 km of the Tagus estuary were, on average, cooler than northern Lisbon during SEB events, especially the areas up to 500 m (average ΔTurb reached −1.7°C). Additionally, there was a significant increase in the moisture content during SEB hours across the city but especially close to the riverfront area: the areas up to 500 m registered, on average, ΔHaurb of 4.2 g/m3 on SEB events (12:00 PM) against 2.1 g/m3 during typical Nortada days. This research is a starting point for a future delimitation and preservation of SEB penetration zones in Lisbon to address outdoor thermal discomfort during summer.
- Local Weather Types by thermal periods: deepening the knowledge about Lisbon’s urban climatePublication . Reis, Cláudia; Lopes, António; Correia, Ezequiel; Fragoso, MarceloUrbanized hot spots incorporate a great diversity of microclimates dependent, among other factors, on local meteorological conditions. Until today, detailed analysis of the combination of climatic variables at local scale are very scarce in urban areas. Thus, there is an urgent need to produce a LocalWeather Type (LWT) classification that allows to exhaustively distinguish di erent urban thermal patterns. In this study, hourly data from air temperature, wind speed and direction, accumulated precipitation, cloud cover and specific humidity (2009–2018) were integrated in a cluster analysis (K-means) in order to produce a LWT classification for Lisbon’s urban area. This dataset was divided by daytime and nighttime and thermal periods, which were generated considering the annual cycle of air temperatures. Therefore, eight LWT sets were generated. Results show that N and NW LWT are quite frequent throughout the year, with a moderate speed (daily average of 4–6 m/s). In contrast, the frequency of rainy LWT is considerably lower, especially in summer (below 10%). Moreover, during this season the moisture content of the air masses is higher, particularly at night. This methodology will allow deepening the knowledge about the multiple Urban Heat Island (UHI) patterns in Lisbon.
- Human thermo-physiological comfort assessment in Lisbon by local climate zones on very hot summer daysPublication . Reis, Cláudia; Nouri, A. Santos; Lopes, AntónioExtreme heat is a current and future issue on urban areas, with negative impacts on health and quality of life (increasing morbidity and mortality rates). This paper analyses day (12:00–15:00 h) and nighttime (00:00–03:00 h) thermophysiological comfort (TC) conditions by Local Climate Zones (LCZ) in Lisbon during a particular Local Weather Type (LWT), very hot summer days. For this, 13 different microscale sample areas were chosen covering urban and non-urban land cover classes (LCZs 1–3, 4–6, 8, 9, A and B). Universal Thermal Climate Index (UTCI) and Mean Radiant Temperature (MRT) were modeled on SkyHelios software for 163 days between 2008 and 2014. Results show that during the day all urban LCZ samples depict the same average TC conditions (average UTCI of 34°C—strong heat stress) and densely wooded areas are 2°C cooler (average UTCI of 32°C—moderate heat stress). However, compact areas (LCZs 1–3) with low sky view factor and some vegetation (street trees) display lower percentages of area with higher thermo-physiological discomfort (TD) levels (83% with strong heat stress against 98% in LCZs 8 and 9 and 100% in LCZs 4–6). When considering the hottest days (air temperatures equal or above 35°C—75th percentile), the moderate heat stress class disappears in all samples and the very strong heat stress class appears only on urban areas, occupying between 12% and 16% on LCZs 1–3, 10%–22% on LCZs 4–6, 16%–22% on LCZs 8 and 9 on LCZ 9. During the nighttime period all samples show no thermal stress, favoring nocturnal physiological recovery. TC conditions in Lisbon are strongly influenced by solar radiation and wind, which explains the need to increase the shading area, preferably by trees, and to promote and preserve ventilation paths.
- Assessing urban heat island effects through local weather types in Lisbon's Metropolitan Area using big data from the Copernicus servicePublication . Reis, Cláudia; Lopes, António; Nouri, A. SantosIn this study UHI in Lisbon's Metropolitan Area (LMA) is analyzed through Local Weather Types (LWT) using an air temperature dataset produced by Copernicus. Over 61,000 hourly air temperature maps between 2008 and 2014 are extracted, divided into thermal seasons and LWT, and UHI is calculated by the anomaly between each raster cell and a pixel from “Low Plants” Local Climate Zone (LCZ) class. UHI daily cycle is analyzed by LWT. Statistical analysis shows that rainy days produce lower median UHI intensities (close to 0 ◦C), while sunny days, especially very cold winter days, produce higher UHI intensities (median values close to 1,5 ◦C). Analysis of the UHI pattern displays a S/SE-N/NW dichotomy in the right bank of the Tagus river and an N-S dichotomy in the Peninsula of Setúbal. The UHI effect is more pronounced in Lisbon, particularly in the riverfront area, and on the opposite bank of Tagus due to the shelter effect of frequent N winds. As previous studies have proven, UHI in LMA is mainly a nighttime phenomenon. This methodology may help decision makers to identify critical heating districts as well as weather conditions most conducive to a significant overheating of the urban atmosphere.
- Climate walking and linear mixed model statistics for the seasonal outdoor thermophysiological comfort assessment in LisbonPublication . Silva, Tiago; Reis, Cláudia; Braz, Diogo; Vasconcelos, João; Lopes, AntónioTo measure urban outdoor pedestrian thermophysiological comfort mobile roving missions were conducted in all seasons of the year during the day and at night. Six routes were chosen, representing areas of the city with varying urban morphological layouts. The thermal comfort conditions were analysed using the Local Climate Zone spatial scale. This enabled the identification of typologies of areas where pedestrians might feel (un)comfortable. To achieve the proposed objectives, quantitative and qualitative analysis were run, namely a Linear Mixed-Effect Model. This model was useful to understand the thermal behaviour of the roved areas by comparison to a reference area. The city was found to be generally cooler, except at night when it can have a 44% increased UTCI. Most collected values throughout the year had ‘no thermal stress’, except in the summer when ‘moderate’ and ‘strong heat stress’ was predominant. Compact and large low rise urban areas were found to be the most uncomfortable. Significant amplitudes were found in some LCZs, reaching as high as 7 ◦C in some scenarios. Sparsely wooded areas exhibited higher values in all seasons and at night, except in the summer. This showed that for a local heat stress analysis a higher resolution scale is needed.