Determination of Urban Thermal Characteristics on an Urban/Rural Land Cover Gradient Using Remotely Sensed Data

K Sithole,Jo Odindi

doi:10.4314/sajg.v4i4.3

Abstract

The transformation from natural to impervious surfaces in an urbanization process and the urban heat island (UHI) phenomenon is known to significantly compromise urban environmental quality and has been linked to climate change and associated impacts. Whereas the existence of UHI is common knowledge, the implication of urban land use land cover (LULC) gradient on intra-urban thermal characteristics is often poorly understood. A recent proliferation of remotely sensed datasets offer great potential in understanding the relationship between urban LULCs and their respective thermal characteristics, a critical basis for urban environmental management and designing climate change mitigation measures. This study explores the potential of multispectral remotely sensed dataset in determining the influence of rural/urban LULC gradient on urban thermal characteristics. A rectangular eleven band Landsat 8 image subset was delineated from the central business district to the rural periphery and classified into most dominant LULCs and a corresponding Landsat 8 thermal layer used to determine the LULCs thermal characteristics. Digitized point data was used to determine differences in land surface temperature (LST) over gradient's LULC types. Results showed that there was varied contribution of LULCs to the LST. As expected, the density of built up surfaces and LST decreased towards the city’s periphery while a decline in vegetation density from the periphery led to an increase in LST. These results provide valuable insights into the value of remotely sensed datasets in understanding the implication of intra-urban LULC gradient on LST characteristics. Specifically, the study demonstrates the value of remotely sensed data as aids to sustainable urban environmental planning.

Highlights

Urbanization has been identified as a major influence to the transformation of land use and land covers (LULCs) and a key driver to environmental change (Kardinal et al, 2007; Xuejie et al, 2003)
Recent insights into urban heat island (UHI) and its implication on climate change has increased the need for an understanding of the influence of urbanisation transformation on urban thermal characteristics (Kardinal et al, 2007; Radhi et al, 2013; Weng, 2001; Zhang and Huang, 2012)
To date, the efficacy traditional techniques like surveys and in situ meteorological data have been impeded by among others lack of integrative and comparative capabilities at relevant spatial resolutions. Due to their relatively lower cost in addition to the above named limitations, remotely sensed datasets have recently become valuable in understanding the relationship of urban LULCs and their respective thermal characteristics (Senanayake et al, 2013; Takeuchi et al, 2010; Xiao-Ling Chen, 2006)

Summary

Introduction

Urbanization has been identified as a major influence to the transformation of land use and land covers (LULCs) and a key driver to environmental change (Kardinal et al, 2007; Xuejie et al, 2003). Remnant natural landscapes and converted impervious LULC mosaics act as thermal sources and sinks respectively (Weng, 2001) These mosaics influence urban Land Surface Temperature (LST) as they determine a surfaces’ solar radiation and absorption, thermal capacity and heat conductivity (Qian et al, 2006). The elevated urban LST is often distinct from the cooler peripheral and rural landscapes, a phenomenon referred to as the Urban Heat Island (UHI) This phenomenon is known to significantly affect micro and macro climate, deteriorate urban environment and has been identified as a major influence to climate change and associated impacts (Timmerman and White, 1997). In this study, using remotely sensed datasets and GIS techniques, we seek to determine the influence of urban/rural LULC gradient on thermal characteristics around the city of Pietermaritzburg

Data and methods

Results and discussion

Conclusions