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Estudo preliminar da precipitação oculta na bacia hidrográfica do Caldeirão Grande (São Miguel - Açores)
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Advisor(s)
Abstract(s)
O arquipélago dos Açores é caracterizado por um clima com elevados índices de humidade, que por vezes pode alcançar os 100%. Os nevoeiros são massas de ar húmido, formados por pequenas gotículas de água suspensas na atmosfera que se capturados podem constituir uma origem de água passível de utilização direta ou indireta, neste caso, por exemplo, para a recarga de aquíferos. Diferencia-se, assim, a designada precipitação horizontal da pluviosidade (precipitação vertical).
O presente estudo de avaliação do potencial associado à precipitação oculta desenvolveu-se na bacia hidrográfica do Caldeirão Grande, situado a uma cota superior a 600 metros, o que configura um local com características favoráveis à ocorrência de nevoeiros e à sua consequente captura. A construção de um coletor padrão de nevoeiro (SFC) permitiu comparar os resultados obtidos neste estudo com outros realizados por todo o mundo.
A recolha de dados iniciou-se a 8 de janeiro de 2019 e prolongou-se até 29 de agosto, perfazendo um total aproximado de oito meses, a que correspondem 65 medições.
Os resultados demonstram que o contributo hídrico proveniente da precipitação oculta é sempre superior ao da precipitação horizontal. No período de estudo observou-se um volume acumulado de precipitação horizontal igual a 3 519 mm, enquanto a precipitação vertical observada corresponde apenas a 1 551 mm. A média diária de precipitação oculta é igual a 64 mm/dia, enquanto o contributo da precipitação vertical é 27 mm/dia.
A distribuição mensal da precipitação oculta mostra que 62% do total ocorre de janeiro a maio. Por seu turno, a precipitação vertical concentra 51% do seu volume nos meses de fevereiro e agosto. Realça-se que o período de estudo correspondeu em parte a um ano hidrológico atípico, devido à elevada concentração de chuva no mês de agosto (23%). O volume captado de precipitação horizontal é maior quando o valor médio da velocidade do vento se encontra abaixo dos 8,1 km/h, e a média de rajadas máximas é inferior a 25 km/h.
Os dados de precipitação oculta produzidos nesta dissertação de mestrado são coerentes com outros dados produzidos noutros estudos, que utilizam o mesmo tipo de SFC. Em casos de estudo desenvolvidos no Chile, Peru, Omã, Equador e na Região Autónoma da Madeira (Portugal) o volume diário de precipitação oculta é igual ou superior a 3 L/m2. No caso particular dos dois estudos realizados na ilha da Madeira por Prada (2000), constata-se que a média diária de precipitação oculta obtida no Caldeirão Grande é intermédia entre os resultados obtidos naquela ilha.
ABSTRACT: The Azores archipelago is characterized by a climate with high humidity levels, which can sometimes reach 100%. Fogs are masses of moist air, formed by small droplets of air suspended in the atmosphere that if captured can constitute a source of water that can be used directly or indirectly, in this case, for example, for the recharge of aquifers. This differentiates between the so-called fog precipitation, or fog harvesting, from rainfall. The present study aims to evaluate the potential associated with fog precipitation and was developed in the Caldeirão Grande watershed, located at an altitude over 600 meters, which constitutes a site with characteristics favorable to the occurrence of fog and its consequent harvesting. The construction of a standard fog collector (CFS) made it possible to compare the results obtained in this study with others performed around the world. Data collection began on 8 January 2019 and lasted until 29 August, totaling approximately eight months of observations, corresponding to 65 measurements. Results show that the water contribution from fog precipitation is always higher than that of rainfall. During the development of the study, an accumulated fog precipitation volume of 3 519 mm was observed, while the rainfall observed was only 1 551 mm. The average fog precipitation is 64 mm/day, while the contribution of average daily rainfall is 27 mm / day. The monthly distribution of fog precipitation shows that 62% of the total occurs from January to May. In turn, rainfall concentrates 51% of its volume in February and August. It is highlighted that the study was made during a period that corresponded in part to an atypical hydrological year, due to the high concentration of rain in August (23%). The amount of fog harvesting is higher when the average wind speed is below 8.1 km/h, and the average maximum wind gust is less than 25 km / h. Fog precipitation data produced in this master's dissertation are consistent with other data produced in other studies made worldwide using the same type of SFC. In case studies developed in Chile, Peru, Oman, Ecuador, and the Autonomous Region of Madeira (Portugal) the daily volume of fog precipitation is higher than 3 L/m2. In the particular case of the two studies carried out on Madeira by Prada (2000), it can be seen that the daily average of fog precipitation obtained in Caldeirão Grande is intermediate between the results obtained on that island.
ABSTRACT: The Azores archipelago is characterized by a climate with high humidity levels, which can sometimes reach 100%. Fogs are masses of moist air, formed by small droplets of air suspended in the atmosphere that if captured can constitute a source of water that can be used directly or indirectly, in this case, for example, for the recharge of aquifers. This differentiates between the so-called fog precipitation, or fog harvesting, from rainfall. The present study aims to evaluate the potential associated with fog precipitation and was developed in the Caldeirão Grande watershed, located at an altitude over 600 meters, which constitutes a site with characteristics favorable to the occurrence of fog and its consequent harvesting. The construction of a standard fog collector (CFS) made it possible to compare the results obtained in this study with others performed around the world. Data collection began on 8 January 2019 and lasted until 29 August, totaling approximately eight months of observations, corresponding to 65 measurements. Results show that the water contribution from fog precipitation is always higher than that of rainfall. During the development of the study, an accumulated fog precipitation volume of 3 519 mm was observed, while the rainfall observed was only 1 551 mm. The average fog precipitation is 64 mm/day, while the contribution of average daily rainfall is 27 mm / day. The monthly distribution of fog precipitation shows that 62% of the total occurs from January to May. In turn, rainfall concentrates 51% of its volume in February and August. It is highlighted that the study was made during a period that corresponded in part to an atypical hydrological year, due to the high concentration of rain in August (23%). The amount of fog harvesting is higher when the average wind speed is below 8.1 km/h, and the average maximum wind gust is less than 25 km / h. Fog precipitation data produced in this master's dissertation are consistent with other data produced in other studies made worldwide using the same type of SFC. In case studies developed in Chile, Peru, Oman, Ecuador, and the Autonomous Region of Madeira (Portugal) the daily volume of fog precipitation is higher than 3 L/m2. In the particular case of the two studies carried out on Madeira by Prada (2000), it can be seen that the daily average of fog precipitation obtained in Caldeirão Grande is intermediate between the results obtained on that island.
Description
Dissertação de Mestrado, Vulcanologia e Riscos Geológicos, 11 de março de 2020, Universidade dos Açores. Faculdade de Ciências e Tecnologia.
Keywords
Bacia Hidrográfica do Caldeirão Grande Hidrologia Precipitação Oculta Vulcanismo Serra Devassa (Açores) Açores Fog Precipitation Hidrology Azores
Citation
Mendonça, Cristóvão Oliveira Horta. "Estudo preliminar da precipitação oculta na bacia hidrográfica do Caldeirão Grande (São Miguel - Açores)". 2020. 74 p.. (Dissertação de Mestrado em Vulcanologia e Riscos Geológicos). Ponta Delgada: Universidade dos Açores, 2019. [Consult. Dia Mês Ano]. Disponível em www:<http://hdl.handle.net/10400.3/5661>.