Abstract
A climatological analysis of the differences in air temperature between rural and urban areas (ΔTu-r) corroborates the existence of an urban heat island (UHI) in Akure (7º 25’ N, 5º 20’ E), a tropical city in the south western part of Nigeria. The investigations which have been conducted out of a year-long experiment from fixed point observations focuses on the description of the climatology of urban canopy heat island in the Akure and the analysis of the results were presented. The results show that the nocturnal heat island was more frequent than the daytime heat island as it exists from less intense to higher intensity categories throughout the study period. Nocturnal heat Island intensity was observed to be stronger during the dry season. Although of lower intensity, daytime heat Island exists throughout the day except for few hours in the months of November and December that exhibits a reverse thermal contrast. The daytime heat island is observed to be intense in the wet months than the dry months, which may be caused by the evaporative cooling of wet surfaces. On the average, the urban/ rural thermal differences are positive, varying from 4°C at nocturnal hours during dry months to an approximate of 2°C around noon during wet months. This paper explain the aspects of heat islands and their relation to other causative agents such as the sky view factor (SVF) and also discusses its potential impact on energy demand. Key words: Urban heat island, sky view factor, energy demand
Highlights
The city of Akure has witnessed remarkable growth in its urbanisation in recent years, and its population during the past few decades has more than tripled
The most essential feature of the annual course of urban canopy heat island in the city is that the greatest differences occur in the dry season reaching 3.5°C and the smallest difference occurs during the wet season
The urban heat island (UHI) has been found to occur throughout the day and night except for a few hours after noon in November and December that existence of urban cool island (UCI), a reversed thermal contrast which may be as a result of relative abundance of moisture in the city compared to the rural surroundings was noticed
Summary
The city of Akure has witnessed remarkable growth in its urbanisation in recent years, and its population during the past few decades has more than tripled. The importance of weather related parameters in determining the amount of energy required to achieve desired human comfort needs to be harnessed, during periods that are associated with high frequency of heat island and warmer nights which are expected to vary in severity by different landuse types. This can be translated into economic value and serve as a basis for policy formulation in urban planning and climate mitigation measures. The sites were selected for fixed point observations and data were obtained from shielded portable Lascar EL-USB-2 temperature/humidity data loggers, sampled at 5-minute intervals that were mounted on a lamp post above head height (3 m) in the city urban centre and on a mast at the same height in the local
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