Rapid urbanisation and industrialisation have resulted in sharp land cover changes. Urban change not only impacts on land cover but also on urban climate. Land surface and atmospheric modifications due to urbanisation generally lead to a modified thermal climate that is warmer than the surrounding, non‐urbanised areas. In this research remote sensing technology was used to evaluate urban growth patterns and its thermal characteristics through mapping impervious surfaces and evaluating thermal infrared images. The case study was carried out in the northern part of Ho Chi Minh City, which has experienced accelerated urban development since the late 1980s. Landsat and Aster images were used to calculate variations in urban impervious surfaces from 1989 to 2006. Thermal bands were processed to obtain radiant surface temperatures for investigating the urban heat island effect associated with increasing impervious surfaces, both spatially and temporally. Impacts of urban development on surface temperature were shown by investigating the surface urban heat island effect intensity. The results show that the built‐up area in the northern part of Ho Chi Minh City expanded by 6.5 times between 1989 and 2006. Urban development has altered the magnitude and pattern of the surface urban heat island, with the highest land surface temperature cores found in the industrial (greater than 45oC) and urban areas (within 36oC and 40oC). In suburban and rural areas, where agricultural land still remains with full vegetation cover, the land surface temperature is usually lower. Using remote sensing, the impervious surface was extracted with overall accuracy and a Kappa coefficient for all three years greater than 96%, and the retrieved land surface temperatures with variations from in‐situ measurements of less than 2oC. The results presented here indicate that remote sensing can help to spatially monitor urban development and land surface temperature changes over the whole area and over a long period of time.
Urban green space, discovered by optical remote sensors, is the area covered by terrestrial vegetation in urban areas, and is considered an important factor in urban sustainability. Two sensors ALOS/AVNIR-2 and Landsat/OLI&TIR were used in this study to determine green space by Maximum Likelihood Classification method. The investigated area was Nha Trang city, located in the central Vietnam. This was found that the impervious surfaces were rapidly increased leading to significantly reduce urban green space within 10 years from 2007-2017. In urban areas, the green index was very low compared to the TCXDVN 9257: 2012. Based on the Markov chain, it is projected that over the next 10 years, the total vegetation cover of the city will continue to decline compared to that of today. This is likely to lead to increase catastrophe and environmental risks, especially floods and erosion in the coastal city of Nha Trang. The process could be very useful in mapping urban green space as indicator serving city sustainable development.
Urbanization is indispensable for the development of humanity. The changes from the urbanization process have a significant impact on other components of natural systems in Ho Chi Minh City. The problem of filling low-lying swamps, ponds, lakes as well as canal encroachment has made significant changes to the shape of the surface topography of the city and particularly affected the current flood situation around the city. The objective of the study was to map changes in surface topography in relation to urbanization process in central part of Ho Chi Minh city during the period 1989-2011. Band ratio method and Maximum Likelihood classification were implemented to separate the objects of urban and low-lying swamp from 3 satellite images in 1989, 2003 and 2011. The change detection has been done by post-classification method combined with GIS and field data to detect changes in the disappearance of low-lying swamps as well as the existence of urban areas on it. Classification process has resulted in an overall accuracy greater than 89% with urban area increased to a half of the entire area within 22 years. Meanwhile the area of low-lying swamps reduced almost 5 times compared to the existing area in the early stage. Research has built spatial maps of the current status and changing as well as carried out the analysis and evaluation to affect flooding in the city. This is a proof of the lack of scientific methods in the urban management and the positive transformation to reduce flooding today is needed.
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