The influence of the urban heat island effect on urban thermal comfort in the Greater Kampala Metropolitan Area (GKMA), Uganda from 2002 -2020

Abstract

Greater Kampala Metropolitan Area (GKMA) as a central hub for industrialization and socio-economic activities has continuously led to land transformations and increasing temperature differences known as the Urban Heat Island (UHI) effect. Numerous research has been done on the UHI in Kampala city but less has focused on its metropolitan area, contribution of land transformations on the temperatures and the impact of the UHI on the urban thermal comfort. This study objectively sought to; analyze the influence of the built-up density on the spatial-temporal patterns of the UHI and determine the influence of the UHI on urban thermal comfort in GKMA. Using Landsat images, ERA5 ReAnalysis data and Geo-information Systems Technology with RayMan model for analysis from 2002 to 2020, results indicated a greater transformation of undeveloped land cover into built-up exacerbating the increase in built-up index– highest increment occurring between 2002 and 2012. In spite of a decrease of Land Surface Temperatures (LST) from 43.740C in 2012 to 32.030C by 2020, there was a strong significant positive correlation between the NDBI and LST in 2002 (0.57) and weak but significant correlation in 2012 (0.24) and 2020 (0.07) attributed to other factors like ENSO climate phenomena, anthropogenic emissions and COVID-19 that influenced the UHI. Physiological Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) thermal indices indicated similar temperature fluctuation patterns with an increase in moderate heat stress hours in 2012 (10 hours), decreasing to 4 hours in 2020 and showing strong correlations with air and surface temperatures throughout the entire period. Temperature Humidity Index (THI) indicated an increase in heat stress health risks from 2002 to 2012 by 7 hours, the threat reducing by 5 hours in 2020 due to a reduction in temperatures. This study unveiled the impact of increasing temperatures on thermal comfort of residents in GKMA which greatly informs the need for urban heat island mitigation measures by various policy makers.