Abstract
Abstract. Urban areas have been cited to be contributors to changing climatic conditions. Conversion of vegetated areas to impervious surfaces causes an alteration of surface temperatures, where impervious surfaces absorb and store incoming radiation during the day, releasing it slowly at night. This causes the urban heat island effect where temperatures in urban areas are higher than rural areas during night. Extreme weather conditions experienced in urban areas include heat waves, intense rainfall resulting to flash floods, destruction of infrastructure facilities. The research involved the use of time-series of stereo-aerial images acquired in 1978, 2000 and 2017. Building footprints were digitized and using digital elevation models, building heights were derived and volumes calculated. Road volumes were calculated using minimum standards of road construction and the total built-up volume was determined. The ground coverage ratio (GCR) and built-up volume densities (BVD) of the built-up areas was calculated from area and volumes from road and building values. Results indicate the mean GCR and BVD in Upper Hill is within the low density range. Mean building height from 1978 to 2017 are in the low-rise range with significant rise in building height and volumes between 1998 and 2017. The 3D built-up intensity expansion rate ranged between −4.28% to 56.80% per annum with a mean of 19.6% per annum. Roads and pavements also have a significant influence on the built-up density and should therefore be considered in planning policies.
Highlights
Space-borne earth observation (EO) is very important in planning for urban areas as it provides up-to-date spatial information
Mean ground coverage ratio (GCR) from 1978 to 2017 is between 11% and 19% while mean built-up volume densities (BVD) is between 55% and 185%, which are within the low density range (Table 4)
Re-zoning policy changes in Upper Hill were approved in 1995 by Nairobi City County (NCC) and this contributed to the increase in built-up densities as seen between 1998 and 2017 (Karoki, 2004;UNEP et al, 2009)
Summary
Space-borne earth observation (EO) is very important in planning for urban areas as it provides up-to-date spatial information. Builtup areas (buildings) and non-built-up areas (open spaces) make up the urban space (Hamaina et al, 2012). Natural features such as trees, vegetation and some man-made objects such as buildings within an urban area comprise a digital image of the earth’s surface and is referred to as a 3D city model (Singh, 2013). Urban systems are better understood through the use of accurate 3D models, resulting to sustainable urban development (Billen et al, 2014). Monitoring the spatial impact of urban planning strategies needs functional and morphological land-use maps that indicates continuing urban growth processes (Van de Voorde et al, 2011). Cities need to be investigated in a holistic way in view of sustainable development of cities where the interrelations of various environmental and urban issues are taken into account (Billen et al, 2014)
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