Urban Morphology, Microclimate, and Outdoor Thermal Comfort in Maiduguri, North East Nigeria

Urban morphology profoundly shapes outdoor thermal environments in hot semi-arid cities like Maiduguri, the capital of Borno State in Nigeria's North East geopolitical zone, where extreme heat events impose thermal stress on outdoor workers, street vendors, and commuters that can reach life-threatening levels during April and May pre-monsoon periods. This study analyses the relationship between urban morphological characteristics and outdoor thermal comfort conditions in Maiduguri using field measurements, morphological analysis, and thermal comfort modelling. Outdoor thermal comfort was assessed using the Physiological Equivalent Temperature index, computed from simultaneous measurements of air temperature, radiant temperature, relative humidity, and wind speed recorded at 24 street-level monitoring stations across six morphologically distinct urban zones. Urban morphological parameters including sky view factor, canyon aspect ratio, vegetation fraction, and albedo were computed from Pleiades very high resolution imagery and field measurements at each monitoring station. The ENVI-met microclimate simulation model was calibrated using field-measured data and applied to generate spatially continuous thermal comfort maps for two representative urban zones. Results confirm that traditional neighbourhood street canyons with high shade provision maintain significantly lower Physiological Equivalent Temperature values relative to modern open boulevard configurations (mean difference of 7.8 degrees Celsius at 14:00 local time in April). Vegetation fraction emerges as the single strongest predictor of thermal comfort improvement, with each 10 percent increase in tree canopy cover associated with a mean PET reduction of 2.3 degrees Celsius. The study recommends bioclimatic urban design guidelines mandating minimum street tree coverage and shade structure requirements for Maiduguri's urban development approvals. Keywords: urban morphology, outdoor thermal comfort, Maiduguri, North East Nigeria, microclimate.