ABSTRACT
The current study assessed the city of Kumasi, Ghana to find out the extent of urban heat and the views of the populace about their climate. Both the subjective and objective approaches were utilized in the study. Secondary data from the Meteorological Survey Department in Kumasi covering temperature and relative humidity values for a 42- year period (1976 - 2018) was retrieved and used in the analysis to find the trend of urban heat phenomenon. Alongside, a developed questionnaire had a response from 2,083 people. The findings reveal among other things that there’s a 2ºC rise in mean annual temperature from 1976 to 2018. Additionally, the data shows that the past 4 years have had high mean temperature values. Subjectively, 1, 271 residence representing 61% voted in the “slightly warm-hot” range on the thermal sensation scale. Majority of the respondents across all the ages indicated how uncomfortable their outdoor spaces have become in recent times. 36% of the respondents attributed this discomfort to the lack of greenery with over 95% across all ages indicating that Kumasi city has lost its greenery and green spaces to buildings and other infrastructural activities. Whiles climate change and global warming have both become a global menace, the onus lies on individual countries and for that matter, various city authorities to make a conscious effort in planning our cities with greenery to alleviate the menace we already find ourselves. A conscious effort to retrieve and restore encroached green spaces must be undertaken by the city authorities while the parks and gardens division ought to be efficiently resourced to manage our green spaces.
ABSTRACT
The Metropolitan Region of Baixada Santista (MRBS) harbors one of the main port areas of Brazil: the Port of Santos. Due to the accelerated urban development in this region, the monitoring of biophysical parameters is fundamental. Therefore, this paper aims to i) estimate the soil surface temperature (Ts) and identify the Urban Heat Islands (UHI) formation; and ii) compare the Ts and the normalized difference vegetation index (NDVI) for MRBS from 1986 to 2016 using Landsat 5 and 8 images. Remote sensing tools are essential to meet the objectives of this work for providing both the spatial and temporal evaluation of a region. The spatial analysis was based on the NDVI to evaluate the vegetation density and size from five previously established classes (i.e., water bodies, urban grid, exposed soil and road corridors, shrub, and dense vegetation). The NDVI mapping showed a significant reduction in the cover area referred to the dense vegetation class (91.7%), while the urban grid category increased by 29.4%, resulting from the urban expansion and green cover reduction over the region during this period. Surface temperature thematic maps showed high-temperature values related to increased urbanization and decreased rainfall. Moreover, an 8°C rise in surface temperature over the last 30 years was registered due to the regional development, which has replaced natural soils by anthropic materials and reduced dense vegetation. This phenomenon has resulted in the formation and intensification of UHI, especially after the 2000s.
A Região Metropolitana da Baixada Santista (RMBS) abriga uma das principais zonas portuárias do Brasil, o Porto de Santos. Devido ao grau de urbanização dessa região, o monitoramento dos parâmetros biofísicos torna-se fundamental. Desta forma, este estudo tem como objetivo i) estimar a Temperatura de superfície terrestre (Ts) da RMBS, seguido da identificação da formação de ICU e ii) relacionar a Ts e o NDVI da RMBS no período de 1986 a 2016, a partir das imagens do Landsat 5 e 8. A análise espacial foi baseada no Normalized Difference Vegetation Index (NDVI), no sentido de verificar as condições da densidade e porte da vegetação a partir de cinco classes previamente estabelecidas (Corpo d'água, Malha urbana, Solo exposto e corredores viários, Substrato Arbustivo e Vegetação densa). Os mapas de NDVI indicam uma redução significativa na área de cobertura correspondente à classe vegetação densa, com o valor de cobertura de 91,7%. Por outro lado, a classe Malha urbana apresentou um aumento de 29,4%, resultantes da expansão urbana e da redução da cobertura verde na RMBS ao longo do período. Os mapas temáticos de Tsmostraram altos valores de temperatura, relacionados ao aumento da malha urbana e redução da precipitação. Além disso, houve um aumento de 8ºC na Ts nos últimos 30 anos, causados pelo avanço do desenvolvimento regional, associados à substituição do solo natural por materiais antrópicos e à redução da vegetação densa. Esses fatores resultaram no surgimento de ICU e sua intensificação a partir dos anos 2000.
Subject(s)
Temperature , Land Use , Time Series Studies , UrbanizationABSTRACT
RESUMO: O crescimento urbano e o decorrente surgimento de ilhas de calor são fatores responsáveis não apenas por mudanças nos padrões de conforto e desconforto térmico urbanos mas também por possíveis impactos no aumento da demanda de energia (em climatização artificial) das edificações urbanas. Países em desenvolvimento, a maior parte deles localizada em regiões tropicais, apresentam taxas de crescimento urbano mais elevadas relativamente aos países desenvolvidos; segundo dados da ONU, no período de 2005 - 2010, a taxa de urbanização dos primeiros foi cerca de cinco vezes mais alta que a dos últimos. Nesse contexto, o objetivo do presente trabalho foi analisar a atual ilha de calor urbana de Curitiba, decorrente de seu considerável crescimento urbano nas últimas décadas, a partir de um monitoramento climático contínuo entre dezembro de 2011 e fevereiro de 2013 por meio de estações meteorológicas localizadas na mancha urbana. Adicionalmente à análise de diferenças na temperatura local, quantificaram-se níveis de conforto/desconforto térmico a fim de se verificar o efeito integrado das diversas variáveis meteorológicas em termos de percentuais de horas em frio, conforto e calor, e suas variações dentro e fora da área urbana. Complementarmente são analisadas implicações da ilha de calor urbana em níveis de conforto em ambientes internos. Verificou-se que a presença de uma ilha de calor na área urbana para combater o frio no inverno acarreta aumento desproporcional do calor em situação de verão, não havendo benefício térmico de maneira geral.
ABSTRACT: Urban growth and the resulting urban heat island effect are not only responsible for variations in thermal comfort and discomfort levels within the city but also for increases in building energy demand for air conditioning. In tropical regions, urbanization rates tend to be the highest: the average annual rate of change of the urban population for the five-year period 2005 - 2010 was just over five times higher in the less developed regions than in the more developed part of the world, following a rising trend. The purpose of this paper was to analyze the urban heat island of Curitiba, which results from its considerable urban growth over the last decades, by means of a long-term climate monitoring between December 2011 and February 2013 with a pair of weather stations within the urban area. Additionally, an analysis was performed with regard to outdoor comfort, so that the combined effect of relevant meteorological variables could be assessed in terms of percentages of cold, comfortable and hot hours and variations in and outside the urban area. Finally, implications of the urban heat island effect on indoor conditions are analyzed. It is concluded that the heat island effect with reductions of cold stress in winter does not offset the occurrence of excess heat in summer, with an overall not advantageous effect.
ABSTRACT
Despite increased interest on the urban heat island (UHI) phenomenon, there are limited UHI studies on cities built using the green-city concept of Sir Ebenezer Howard [1]. The administrative capital of Malaysia, Putrajaya is one of such cities built using the green-city concept. The objective of this study was to confirm the effectiveness of the green city concept using the National Centre for Atmospheric Research (NCAR) numerical technique. Numerical mesoscale Weather Research and Forecasting (WRF) Model was coupled with Noah land surface model and a single layer urban canopy model (UCM) to investigate the existence and distribution of UHI, and the behavior of urban canopy layer (2-m) temperature of Putrajaya city. Few studies have been conducted using the NCAR numerical technique (WRF) to explore Malaysian climatology. Suitability of the model employed in studying UHI phenomenon of Putrajaya city was determined using in-situ study of the area, and observational data from AlamSekitar Malaysia SdnBhd (ASMA). Contribution of urban fabrics on the spatial and temporal variations of UHI was also investigated. Comparison with ASMA and in-situ data revealed a satisfactory performance of the model.UHI intensity (UHII) of Putrajaya exhibits a diurnal profile; increasing during the night to a peak value and then diminishing towards morning with a negligible value in the mid-day. In the night time, the UHII ranges from 1.9ºC to 3.1ºC in some of the precincts considered. However, the overall effect of the urbanized areas (local climate zones) on the UHI magnitude was normalized by the total amount of area reserved for vegetation.
ABSTRACT
Aims: The study of urban heat islands and traditionally relies on simplistic descriptors such as “urban” and “rural”. While these descriptors may be evocative of the landscape, they are insufficient in providing information like its site properties which have direct impacts on the surfacelayer climate. The newly developed “Local Climate Zones” (LCZ) characterization scheme from Oke and Stewart [1] was applied to three case study areas to provide a more objective assessment of the urban heat island (UHI) phenomenon in Singapore. Study Design: The three step procedure of site metadata collection, definition of the thermal source area, and selection of the appropriate climate zone was followed for the three case study areas representing green space, a typical high rise residential housing area, and the CBD to identify and explain UHI characteristics. Place and Duration of Study: Singapore; January-March, 2014. Methodology: Characterization of the three study sites included scoring of a sky view factor, canyon aspect ratio, terrain roughness, building surface fraction, impervious surface fraction, surface energy admittance, surface albedo, and anthropogenic heat flux based on observation, photography, and Google Earth imagery, to determine the LCZ class. Temperature, wind speed, and relative humidity were recorded on an hourly basis at each site using Kestrel 4000 weather trackers and data logger at a 2 m elevation for five consecutive days in January, 2014. Results: The three study sites were characterized as LCZ 1 (compact high rise (CBD)), LCZ 4 (open high rise (high rise residential housing area)), and LCZ 9 (sparsely built (green space)). The temperature for LCZ 9 was lower than the other two sites, with the greatest UHI intensity (difference between mean air temperature being 2.01ºC between LCZ 4 and LCZ 9. Interestingly, although the CBD area was warmer than the open high rise area between midnight and 6 a.m., a typical UHI phenomenon, the mean air temperature for the entire 5 day period was greater at the open rise site. Conclusion: The lower temperature at the green space site emphasizes the importance of such spaces in the urban landscape as a means to make cities more liveable and resilient to climate change impacts. The higher mean temperature at the open high rise site as compared to the CBD site was related to anthropogenic activities (particularly traffic patterns), landscaping/green space, and the influence of a large green-certified building within the circle of influence at the CBD site. Overall, the use of LCZ in quantifying the UHI magnitude of Singapore was relatively straightforward to apply and this approach should be widely applied to more objectively investigate the UHI phenomenon, particularly in tropical cities.