Spatial Analysis of Surface Urban Heat Islands in Four Rapidly Growing African Cities

Abstract

Africa’s unprecedented, uncontrolled and unplanned urbanization has put many African cities under constant ecological and environmental threat. One of the critical ecological impacts of urbanization likely to adversely affect Africa’s urban dwellers is the urban heat island (UHI) effect. However, UHI studies in African cities remain uncommon. Therefore, this study attempts to examine the relationship between land surface temperature (LST) and the spatial patterns, composition and configuration of impervious surfaces/green spaces in four African cities, Lagos (Nigeria), Nairobi (Kenya), Addis Ababa (Ethiopia) and Lusaka (Zambia). Landsat OLI/TIRS data and various geospatial approaches, including urban–rural gradient, urban heat island intensity, statistics and urban landscape metrics-based techniques, were used to facilitate the analysis. The results show significantly strong correlation between mean LST and the density of impervious surface (positive) and green space (negative) along the urban–rural gradients of the four African cities. The study also found high urban heat island intensities in the urban zones close (0 to 10 km) to the city center for all cities. Generally, cities with a higher percentage of the impervious surface were warmer by 3–4 °C and vice visa. This highlights the crucial mitigating effect of green spaces. We also found significant correlations between the mean LST and urban landscape metrics (patch density, size, shape, complexity and aggregation) of impervious surfaces (positive) and green spaces (negative). The study revealed that, although most African cities have relatively larger green space to impervious surface ratio with most green spaces located beyond the urban footprint, the UHI effect is still evident. We recommend that urban planners and policy makers should consider mitigating the UHI effect by restoring the urban ecosystems in the remaining open spaces in the urban area and further incorporate strategic combinations of impervious surfaces and green spaces in future urban and landscape planning.

Land Surface Temperature Retrieval from Landsat 5, 7, and 8 over Rural Areas: Assessment of Different Retrieval Algorithms and Emissivity Models and Toolbox Implementation

“…dε is a term accounting for the cavity effect, which depends on the surface geometry. Pv (also referred to as fractional vegetation cover, FVC) is the proportion of vegetation calculated as [103]: (19) where NDVI max = 0.5 and NDVI min = 0.2 in a global situation [70]. As Valor and Caselles [82] suggested, ε v and ε s as 0.985 and 0.960, respectively, for unknown emissivity and vegetation structures, we also regarded these emissivity values in the calculation.…”

“…Land Surface Temperature (LST) represents the temperature of the Earth's surface, and it is one of the key parameters that affect surface energy balance, regional climates, heat fluxes, and energy exchanges [4][5][6][7][8][9][10][11][12][13][14][15]. Many researchers have investigated the importance and effects of LST on various topics, including urban climate and Surface Heat Island (SHI) studies [16][17][18][19][20], evapotranspiration [21], forest fire monitoring [22], geological, and geothermal studies [23][24][25][26][27]. Besides, LST has been approved as one of the high-priority parameters for the International Geosphere and Biosphere Program (IGBP) [7,28].…”

The Impacts of Landscape Changes on Annual Mean Land Surface Temperature in the Tropical Mountain City of Sri Lanka: A Case Study of Nuwara Eliya (1996–2017)

“…The LSTI was calculated based on the urban-rural gradient analysis approach, which involves the creation of concentric rings or buffer zones around the city center with standard distance intervals extending to the rural areas [13,14,42]. Urban-rural gradient analysis has been conducted to identify the spatial and temporal variations in environmental variables in many previous environmental studies [13,14,16,20,60,61]. In this study, thirty-five 210 m buffer zones (hereafter referred to as urban-rural zones (URZs)) were created for the study area.…”

Impacts of Land Cover/Use on the Urban Thermal Environment: A Comparative Study of 10 Megacities in China

“…It is critical to compare the responses of various types of land cover to different regional thermal environments [72,73]. After delineating the spatial layouts of the thermal environments, to examine the thermal contributions of each kind of land cover in different regions, we introduced the thermal effect contribution index (TECI), the weighted thermal unit index (T 1 ), and the regional weighted thermal unit index (T 2 ) [74][75][76].…”