CR 79:127-137 (2019)  -  DOI: https://doi.org/10.3354/cr01584

ABSTRACT: Cloud amounts, their spatial distribution, and the sky view factor (SVF) all have effects on the nocturnal upwelling longwave radiation and result in different degrees of urban-rural radiation cooling, which are widely investigated in studies of the urban heat island phenomenon. Currently, most research studies discuss the influence of synoptic conditions and urban geometric morphology on urban heat islands. Here we attempted to determine the influence of cloud cover on the relationship between the SVF and nocturnal urban heat islands by calculating the SVF considering the cloud amount and its distribution. The Adelaide central urban area of South Australia was selected as the study area, and we used urban 3-dimensional building data with a spatial resolution of 1 m and field measurement meteorological data, as well as ceilometer-observed cloud data. We sequentially analyzed the influence of cloud amount on the instantaneous nocturnal urban heat island intensity (UHII), SVF, and SVF-UHII relationship. The SVF-UHII feature space was then constructed to explain the nocturnal urban heat island. The results reveal that there are high negative correlations between the total cloud amount and UHII, while the correlations change with site location. The cloud amount has an effect on the defined SVF. SVFs at all sites gradually increase with the cloud amount, and the SVF differences between various sites decrease with increasing cloud amount. The SVF-UHII feature space can be preliminarily used to explain and simulate the UHII at some sites under different cloud cover conditions, and the mean relative error of the simulated UHII for the example data was 20%.

KEY WORDS: Cloud cover · Sky view factor · Urban heat island · Feature space