Urban growth implies significant modifications in the urban climate. To understand the influence of the city of Lisbon on the urban boundary layer, a mesoscale meteorological network was installed in 2004. The main goals of the present study are to update the results of the research published in 2007 and to bring more precise information about the relationship between the Urban Heat Island (UHI) and the regional and local wind systems. The highest frequencies of the UHI were found in the city centre (Restauradores). In the green park of Monsanto, the highest frequency occurred between −2 and 0°C. During the summer, the effect of the breezes was observed in Belém, lowering the temperature. The “strong” UHI (intensity >4°C) occurred more often during the summer, with median values of 2°C by night and 1.8°C by day. The highest frequencies of UHI occurred for winds between 2 and 6 m/s and were not associated with atmospheric calm, as pointed out in the literature. Winds above 8 m/s inhibit the occurrence of strong UHI in Lisbon. Summer nighttime strong UHI should be further investigated, due to the heat stress consequences on the population and probable increase of energy consumption.

In memoriam Henrique andrade abstract -With the aim of implementing climatic guidelines for planning purposes, the urban climate of each particular city must be assessed, particularly the frequency of unwanted climatic features, such as the Urban Heat island (UHi). as the Lisbon "Mesoscale urban meteorological network" (CeG-iGOt-ULisboa) has been running since 2004, it is now possible to present statistical results about the UHi. it was calculated on an hourly basis as the difference between one of the "central" measurement points (restauradores or saldanha) and one of the eccentric points of the network (Carnide or Monsanto). UHi is more intense in summer (maximum hourly averages up to 6.3ºC) than in winter (up to 3.8ºC), and more intense during the night than during the day. in Lisbon, its causes are not only due to the modification of energy balance in urban areas, but also to the shelter effect from the prevailing and cold/cool north winds, due to the topography and the buildings. Alcoforado, A. Lopes, E. Lima Alves and P. Canário o clima urbano de cada cidade, nomeadamente no que diz respeito à frequência de ocorrência de fenómenos considerados indesejáveis, como a ilha de calor (iC) urbana. Depois de 8 anos de funcionamento da "rede de mesoscala" de monitorização meteorológica em Lisboa (CeG-iGOt-ULisboa), é agora possível apresentar resultados estatísticos sobre a iC. É expli cada metodologia de cálculo da intensidade da ilha de calor, pela diferença entre um dos postos "centrais" (restauradores ou saldanha) e um dos postos mais excêntricos (Carnide ou Monsanto). a iC é mais intensa e frequente no Verão (valor máximo horário: 6,3ºC) do que no inverno (valor máximo: 3,8ºC) e é mais intensa de noite do que de dia. em Lisboa, as causas da iC devem-se não só à modificação de parâmetros do balanço energético em meio urbano, como também ao efeito de abrigo de ventos dominantes frios ou frescos do quadrante norte, proporcionado pela topografia e pelos próprios edifícios. Key-words:Palavras-chave: ilha urbana de calor, padrões térmicos, rede mesoclimática, Lisboa, Portugal.résumé -étude StatiStique de l'Îlot de chaleur à liSBonne. La connaissance des climats urbains est nécessaire à une juste appréciation des décisions à prendre dans le cadre de l'aménagement du territoire, et surtout en ce qui concerne la fréquence des phénomènes dits indésirables, comme l'îlot de chaleur urbain (iC). Un réseau «d'échelle moyenne» d'observations météorologiques ayant fonctionné à Lisbonne de 2004 à 2012 (CeG-iGOt-ULisboa), on peut déjà présenter des résultats statistiques concernant l'iC. Le calcul de son intensité est basé sur la différence entre les données d'un poste «central» (restauradores ou saldanha) et celles d'un des postes les plus excentriques (Carnide ou Monsanto). L'îlot de chaleur est plus intense et plus fréquent en été (valeur maximale horaire de 6,3ºC), qu'en hiver (valeur maximale de 3,8ºC) et il est plus fort la nuit que le jour. À Lisbonne, les causes de l'iC sont dues non seulement aux modifications des ...

Abstract:In recent years, SUHIs (surface urban heat islands) have been greatly emphasized in urban climate studies, since it is one of the climate phenomena most influenced by human action. In this study, temporal and spatial variations of SUHIs in the cities of Ceres and Rialma (Brazil) were investigated; satellite Landsat 8 TIRS/OLI images from 2013 to 2016 were used for this purpose. The results showed that in all seasons, two relationships were observed, one positive and one negative. An NDV I (Normalized Difference Vegetation Index) of 0.2 is the divider of this relationship: up to this value, the relationship is positive, that is, the higher the NDV I value, the higher the surface temperature, while the relationship is negative at an NDV I greater than 0.2. There was high seasonal variation in the SUHIs, with the highest intensities recorded in the spring and summer (±12 • C), and the lowest in the winter. These temporal variations were attributed to the annual cycle of precipitation, which directly involves the robustness of the Cerrado vegetation. SUHIs occupied, on average, an area three times larger than the area of SUCIs (surface urban cool islands). The highest values of SUCIs were observed in water bodies and in valley bottoms. Overall, SUHIs showed high intensities; however, a more intense core area, such as in large cities, was not observed.