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Clima e ordenamento do território no Funchal
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Neste trabalho, o clima do Funchal é estudado nas suas múltiplas vertentes. O principal objetivo foi o de sintetizar toda a informação climática, aplicando-a ao ordenamento do território, do modo a contribuir para a melhoria do conforto e saúde humana e segurança dos seus habitantes e dos seus bens. O crescimento urbano do Funchal, condicionado pela orografia que limita a sua expansão em continuum, extravasou as fronteiras do limite administrativo do concelho em direção às áreas limítrofes. No centro da cidade as bandas de edifícios foram construídas perpendicularmente aos cursos de água canalizados e, por conseguinte, paralelamente ao litoral, fazendo com que atualmente, a ventilação da atmosfera urbana inferior seja bastante limitada pela barreira arquitetónica, aspeto que tende a aumentar o risco de stresse térmico. Por outro lado, o caráter turbulento do escoamento hidrológico deixa a cidade também vulnerável ao risco de aluviões. Os elementos do clima observados (precipitação, vento, temperatura e humidade do ar) foram tratados estatisticamente e interpretados em complemento com os resultados obtidos com base em vários métodos de estimação espacial: a) a krigagem e a regressão linear simples para a precipitação, sendo que o primeiro se revelou mais adequado para a estimação das precipitações subdiárias; b) a modelação numérica do escoamento atmosférico (vento regional) sobre a ilha; c) a modelação da dispersão de partículas na Baixa do Funchal; d) a regressão múltipla utilizada na interpolação regional da temperatura do ar e da PET (Physiological Equivalent Temperature); e) e a modelação atmosférica de micro-escala da componente térmica do clima no Funchal. A distribuição espacial e temporal da precipitação foi analisado em detalhe. O regime de precipitação na Madeira é caracterizado pela forte variabilidade interanual que, tudo indica, estar relacionada com o padrão da North Atlantic Oscillation (NAO). As precipitações mais intensas e concentradas são mais prováveis nos relevos da vertente sul da ilha, do que nos da vertente norte, ao contrário do que sucede com os quantitativos anuais médios, que são claramente mais elevados na vertente norte. De acordo com a análise de suscetibilidade às precipitações intensas e aluviões, as áreas menos vulneráveis estão localizadas principalmente no sector oeste do concelho, enquanto as mais vulneráveis se localizam sobretudo na cintura intermédia do concelho, acima de 500 m de altitude. As características do vento dominante de nordeste, ao qual estão associados vários efeitos atmosféricos de mesoescala, como as esteiras de turbilhão em redor da ilha ou alongadas para sotavento desta, a aceleração e a separação do fluxo da superfície depois de ultrapassarem os relevos principais têm efetivamente uma grande importância na ocorrência dos tipos de tempo locais e no clima urbano do Funchal, criando um mosaico de padrões termo higrométricos, que deverão ser tidos em conta no ordenamento territorial. Esta separação do fluxo geral permite a ativação dos sistemas de circulação local a sotavento, numa atmosfera estável, com o desenvolvimento duma inversão térmica de subsidência pronunciada sobre a cidade. Contudo os dois sistemas de ventos funcionam em articulação, na medida em que a brisa do mar tende a soprar com maior intensidade quando a sua corrente de retorno é reforçada pelo vento de NE, também ele mais forte e regular no topo da montanha. De dia, a circulação de brisa do mar, cujo quadrante predominante é o SW, representa o tipo de regime de vento mais frequente em todas as estações do ano, sendo que no verão ocorre em quase 80% dos dias e no inverno em 45%. A partir da análise efetuada entre a circulação das brisas de mar e de montanha e a concentração de poluentes atmosféricos no Funchal (em particular no que se refere à concentração de PM10) demonstrou-se que ocorre um aumento progressivo das concentrações ao longo do período diurno nos principais corredores de circulação viária, em parte explicado pelo efeito de acumulação das emissões dos veículos automóveis. Ao contrário do que sucede noutras cidades, no Funchal ocorre apenas um pico diário de concentração de PM10 coincidente com a hora de ponta da tarde e com a fase de diminuição da velocidade da brisa do mar. Os máximos horários podem atingir frequentemente valores na ordem das 50 a 60 μg/m3, sendo que nas primeiras 3 a 4 horas da noite, as concentrações de PM10 permanecem elevadas, numa altura do dia em que a circulação das brisas de terra e de montanha ainda são bastante fracas. Mas não só não foram observados picos de concentração de PM10 na hora de ponta da manhã, como nesta altura do dia ocorrem normalmente os valores mínimo diários, devido possivelmente à persistência da circulação da brisa de montanha, que favorece a dispersão das partículas. Ao nível do planeamento urbano mostrou-se igualmente que se deve promover a ventilação de modo a reduzir os efeitos nefastos dos poluentes atmosféricos no Funchal. Conclui-se que, para manter os níveis de PM10 em valores abaixo dos máximos exigidos por lei, será necessário reduzir em 50% o número de viaturas nas principais vias de comunicação nas horas de pico. O conforto bioclimático foi estudado através da análise das frequências de ocorrência de variáveis como a temperatura e a humidade do ar e a PET. Os níveis de humidade mantêm-se elevados nas áreas mais abrigadas da brisa do mar, no interior da cidade, em especial no período diurno (acima de 60%), diminuindo durante a noite, principalmente nos locais mais expostos à drenagem noturna do ar fresco da montanha. No litoral, a situação de tempo quente e húmido a meio da tarde, dada pelo limiar de tensão de vapor de 18 hPa é a mais frequente de junho a outubro (40% dos dias em cada mês), atingindo uma frequência máxima de julho a setembro (80 a 90%). Nesse tipo de tempo de verão o clima do Funchal é na generalidade confortável (com sensação térmica de “ligeiramente quente”), em todos os locais de medição, mesmo no interior da malha urbana, pese embora muito próximo do limiar entre condição de “ligeiramente quente” e “quente”, o que, nalguns locais, poderá gerar situação de stresse térmico moderado. Por fim foram delimitadas as Unidades de Reposta Climática Homogénea (URCH), às quais se adicionou informação sobre as áreas de suscetibilidade hidrológica (hidroclimatopos), de poluição por partículas e de desconforto térmico por excesso de calor, apresentando-se subsequentemente um conjunto de orientações climáticas espacializadas, traduzidas em medidas para melhorar as componentes do clima urbano consideradas adversas para a saúde e conforto humano, ou que ponham em causa a segurança de pessoas e bens.
In this work, the climate of Funchal is studied in its many facets. The main goal was to synthesize the climate information, applying it to spatial planning, in order to contribute to the improvement of comfort and human health and to the safety of its inhabitants and their assets/properties. The urban growth of Funchal, which expansion reached beyond the boundaries of the municipality’s’ administrative limit toward the neighbouring areas was overtime forced by the relief. In the city centre, the buildings were built perpendicular to the channelled water courses and, therefore, parallel to the coast, in such a way that currently, the urban canopy layer ventilation is rather limited by the building barrier, which tends to increase the risk of heat stress. On the other hand, the turbulent character of water flow enhances the city’s vulnerability to the risk of flash floods. The observed climate elements (precipitation, wind, air temperature and humidity) were statistically treated and interpreted in addition to the results obtained from several spatial interpolation methods: a) kriging and simple linear regression for the precipitation (the first having proved more suitable for the estimation of sub-daily precipitation); b) numerical simulation of the wind flow over the island; c) modelling particle dispersion in the downtown of Funchal; d) multiple regression used in regional interpolation of air temperature and PET (Physiological Equivalent Temperature); e) atmospheric modelling of thermal climate micro-scale component in Funchal. The spatial and temporal distribution of the rainfall was analysed in detail. The precipitation regime of Madeira is characterized by strong inter-annual variability that it seems to be related to the North Atlantic Oscillation (NAO) pattern. The intense and concentrated rainfall events, that trigger floods, seem to be more frequent on the southern part of the island than on the north side, contrary to what happens with the total annual average that is clearly higher on the northern side of the island. According to the intense rainfall and flash floods susceptibility analysis, the less vulnerable areas are located mainly in the municipality’s western sector, while the more vulnerable areas are predominantly located in the intermediate band of county, above 500 m altitude. The characteristics of the northeast prevailing wind, which are associated with various mesoscale atmospheric effects, such as the Von Karman Vortex Streets around and downwind the island, the flow acceleration and separation from the surface after overcoming the mountains, actually have a great importance in the occurrence of weather types and in Funchal urban climate. These factors generate a thermo-hygrometer pattern mosaic, which should be taken into consideration in spatial planning. The surface separation of regional wind allows the activation of downwind local breezes, in the stable atmosphere, with the development of a pronounced subsidence thermal inversion over the city. However, the two wind systems operate together, to the extent that the sea breeze tends to blow out with higher intensity when its return current is reinforced by the strong and regular NE wind at the top of the mountain. By day, the sea breeze, whose predominant quadrant is SW, represents the most frequent wind type throughout the year. In summer it occurs in almost 80% of the days and in winter in 45% of the days. The relation between the sea breeze and the mountain breeze circulation and air pollutants concentration in Funchal (namely PM10), was also studied. It has been demonstrated that there is a progressive increase in concentrations during the day in the main traffic streets, partially explained by the accumulation effect of motor vehicles emissions. Unlike in other cities, in Funchal a single daily peak of PM10 concentration occurs, corresponding to the afternoon traffic peak time and with the end phase of sea breeze circulation. The hourly maximum can often achieve values of around 50 to 60 ug/m3. During nighttime when the mountain breeze are still quite weak (the first 3 to 4 hours), the PM10 concentrations remain high. But not only peak concentration of PM10 were not observed during the morning rush hour, as at this time of the day the minimum daily values are usually observed, due probably to the persistence of the mountain breeze, which favours the particles dispersion. In the context of the urban planning it is important to promote ventilation with the aim of reducing the adverse effects of air pollutants in Funchal. It was concluded that it will be necessary to reduce by 50% the amount of vehicles circulating on the main roads during rush hours, in order to maintain the levels of PM10 values below the maximum required by law. The human bioclimatic comfort assessment was conducted with air temperature and humidity and PET. The humidity levels remain high in the areas sheltered from sea breeze, in the inner city, especially during the day (above 60%), decreasing during the night, especially in the locations exposed to nocturnal drainage of fresh mountain air. Near the seashore, hot and humid weather, given by the 18 hPa vapor pressure threshold, is the most frequent situation from June to October (40% of the days in each month) in the afternoon, with a maximum frequency from July to September (80 to 90 % ). In this type of summer weather, Funchal climate is generally comfortable (with a thermal sensation of "slightly warm") in all measurement locations, even within the urban fabric, although very close to the threshold that separates the "slightly warm" and "hot" condition, which, in some places, may generate a situation of moderate heat stress. Finally, “homogeneous climatic-response units” and spatial climatic guidelines to the urban planning were prepared. In a certain way, this is an innovative assessment because, along with more traditional climatopes, it includes hydroclimatops (areas with some kind of hydrological risk), vulnerable lines of traffic air pollution and the areas with thermal discomfort by excessive heat. The proposed measures in the climatic guidelines are fundamental to improve the components of urban climate that are considered adverse to health and human comfort, or which endanger the safety of persons and properties.
In this work, the climate of Funchal is studied in its many facets. The main goal was to synthesize the climate information, applying it to spatial planning, in order to contribute to the improvement of comfort and human health and to the safety of its inhabitants and their assets/properties. The urban growth of Funchal, which expansion reached beyond the boundaries of the municipality’s’ administrative limit toward the neighbouring areas was overtime forced by the relief. In the city centre, the buildings were built perpendicular to the channelled water courses and, therefore, parallel to the coast, in such a way that currently, the urban canopy layer ventilation is rather limited by the building barrier, which tends to increase the risk of heat stress. On the other hand, the turbulent character of water flow enhances the city’s vulnerability to the risk of flash floods. The observed climate elements (precipitation, wind, air temperature and humidity) were statistically treated and interpreted in addition to the results obtained from several spatial interpolation methods: a) kriging and simple linear regression for the precipitation (the first having proved more suitable for the estimation of sub-daily precipitation); b) numerical simulation of the wind flow over the island; c) modelling particle dispersion in the downtown of Funchal; d) multiple regression used in regional interpolation of air temperature and PET (Physiological Equivalent Temperature); e) atmospheric modelling of thermal climate micro-scale component in Funchal. The spatial and temporal distribution of the rainfall was analysed in detail. The precipitation regime of Madeira is characterized by strong inter-annual variability that it seems to be related to the North Atlantic Oscillation (NAO) pattern. The intense and concentrated rainfall events, that trigger floods, seem to be more frequent on the southern part of the island than on the north side, contrary to what happens with the total annual average that is clearly higher on the northern side of the island. According to the intense rainfall and flash floods susceptibility analysis, the less vulnerable areas are located mainly in the municipality’s western sector, while the more vulnerable areas are predominantly located in the intermediate band of county, above 500 m altitude. The characteristics of the northeast prevailing wind, which are associated with various mesoscale atmospheric effects, such as the Von Karman Vortex Streets around and downwind the island, the flow acceleration and separation from the surface after overcoming the mountains, actually have a great importance in the occurrence of weather types and in Funchal urban climate. These factors generate a thermo-hygrometer pattern mosaic, which should be taken into consideration in spatial planning. The surface separation of regional wind allows the activation of downwind local breezes, in the stable atmosphere, with the development of a pronounced subsidence thermal inversion over the city. However, the two wind systems operate together, to the extent that the sea breeze tends to blow out with higher intensity when its return current is reinforced by the strong and regular NE wind at the top of the mountain. By day, the sea breeze, whose predominant quadrant is SW, represents the most frequent wind type throughout the year. In summer it occurs in almost 80% of the days and in winter in 45% of the days. The relation between the sea breeze and the mountain breeze circulation and air pollutants concentration in Funchal (namely PM10), was also studied. It has been demonstrated that there is a progressive increase in concentrations during the day in the main traffic streets, partially explained by the accumulation effect of motor vehicles emissions. Unlike in other cities, in Funchal a single daily peak of PM10 concentration occurs, corresponding to the afternoon traffic peak time and with the end phase of sea breeze circulation. The hourly maximum can often achieve values of around 50 to 60 ug/m3. During nighttime when the mountain breeze are still quite weak (the first 3 to 4 hours), the PM10 concentrations remain high. But not only peak concentration of PM10 were not observed during the morning rush hour, as at this time of the day the minimum daily values are usually observed, due probably to the persistence of the mountain breeze, which favours the particles dispersion. In the context of the urban planning it is important to promote ventilation with the aim of reducing the adverse effects of air pollutants in Funchal. It was concluded that it will be necessary to reduce by 50% the amount of vehicles circulating on the main roads during rush hours, in order to maintain the levels of PM10 values below the maximum required by law. The human bioclimatic comfort assessment was conducted with air temperature and humidity and PET. The humidity levels remain high in the areas sheltered from sea breeze, in the inner city, especially during the day (above 60%), decreasing during the night, especially in the locations exposed to nocturnal drainage of fresh mountain air. Near the seashore, hot and humid weather, given by the 18 hPa vapor pressure threshold, is the most frequent situation from June to October (40% of the days in each month) in the afternoon, with a maximum frequency from July to September (80 to 90 % ). In this type of summer weather, Funchal climate is generally comfortable (with a thermal sensation of "slightly warm") in all measurement locations, even within the urban fabric, although very close to the threshold that separates the "slightly warm" and "hot" condition, which, in some places, may generate a situation of moderate heat stress. Finally, “homogeneous climatic-response units” and spatial climatic guidelines to the urban planning were prepared. In a certain way, this is an innovative assessment because, along with more traditional climatopes, it includes hydroclimatops (areas with some kind of hydrological risk), vulnerable lines of traffic air pollution and the areas with thermal discomfort by excessive heat. The proposed measures in the climatic guidelines are fundamental to improve the components of urban climate that are considered adverse to health and human comfort, or which endanger the safety of persons and properties.
Descrição
Tese de doutoramento, Geografia (Geografia Física), Universidade de Lisboa, Instituto de Geografia e Ordenamento do Território, 2015
Palavras-chave
Teses de doutoramento - 2015