Outdoor thermal comfort of residents in a warm humid climate : A study on informal settlements in Dar es Salaam, Tanzania

Abstract: In the informal settlements of warm humid climates, where the majority of urbanites spend most of their time outdoors, a conducive thermal environment is crucial for their social and economic well-being. The overall aim of this thesis is to increase knowledge and understanding of outdoor thermal comfort in informal settlements in the warm and humid climate of Dar es Salaam, Tanzania. Urbanites’ thermal perception and coping strategies during different seasons (wet and dry) were investigated using micrometeorological measurements and structured questionnaires. Spatial and temporal variations of outdoor thermalcomfort and various measures (vegetation and building height) to improve thermal comfort were investigated using a simulation model (ENVI-met 4.4.3). Two informal settlements, Kawe located near the coast of the Indian Ocean and Tandale located 5 km inland, were selected. Thermal comfort was estimated using three different thermal indices (PET, SET' and UTCI). The comfort range in informal settlements is shown to be narrower and higher than in formal areas, and the lack of adaptive options causes poorer thermal conditions for the urbanites. Higher comfort ranges indicate higher adaptive capability of the urbanites and reveals their tolerance of higher index temperatures. Th e study noted marginal variations in maximum air temperature between seasons, but thermal comfort relief in the dry (cool) season is linked to the substantial decrease in air humidity. Incremental increase of building height in a street canyon to 12, 18, and 24 m reduces PET by 2.5, 2.8, and 3.8°C respectively at 14:00. Similarly, varying leaf area index by 2, 4, and 6 m2/m2 leads to a reduction of the Tmrt by 7.9, 10.1, and 12.2°C, and PET was reduced by 3.9, 4.7, and 5.6°C respectively at 14:00, which emphasises that shade from trees is an effective measure to reduce heat in the tropics. The study reinforces the necessity to upgrade informal settlements and employ climate-sensitive urban design, integrating the influence of microclimate and thermal comfort. Further studies to investigate the effect of climate change on the microclimate and on urbanites’ thermal perception in informal settlements of warm humid climates is recommended.