URBAN HEAT ISLAND AND ITS EFFECT ON DIURNAL TEMPERATURE RANGE IN AKURE, NIGERIA

Abstract

This study assesses the effect of Urban Heat Island (UHI) on Diurnal Temperature Range (DTR) in Akure, Ondo State. Air temperature data measured simultaneously at 17 different sites within the Akure metropolis in the year 2010 were utilized in this study. The portable thermocron i-button temperature sensors/data loggers were shielded and sampled at 15 – minute intervals. The sensors were mounted on a lamp post above head height (3m) at the selected sites which represent different land use types within the city. The method adopted for this research requires the difference in air temperatures between the city and the out of town stations (ΔTu-Tr), which is the most recognized index of the urban heat island. In addition, the diurnal temperature range (Tmax - Tmin) and the warming / cooling rates were also considered. The result of this study showed that the monthly variations of air temperature during dry season months at the sub-urban and major urban sites (State Secretariat, Oja Oba and Oshinle Quarters) exhibit higher air temperature than average throughout the year. As a result of their close proximity and similarities in morphology and geometry, the sub-urban stations also showed similar trend. The temperature trend observed in all the sites showed that they all have their maxima during the dry season, in the months of February/March and minimum air temperatures during the summer monsoon/rainy season with the lowest values (23.34oC) in August, during the August break. It was also observed for all the sites that DTR are higher during the dry season months, lower during the summer monsoon and lowest in August, during August break. The rural reference site (Airport) has the highest DTR (20.1oC) while the City Park (urban greens) and Futa green area recorded the lowest DTR value of (5oC) throughout the year. Other results also showed that both urban heat island (UHI) and urban cool island (UCI) phenomenon exist within the city of Akure. The UHI phenomenon was observed to be predominant and having its peak during the intensity nocturnal hours and lesser during the day 3 time. UCI was only observed on few occasions in the afternoon. Results of the diurnal pattern of warming and cooling rates revealed that the rural site warms and cool faster than the urban peripheries, while urban greens/park maintains a very low warming and cooling due to the shading factors of the tree canopies. It was however established that the urban heat island effect on the diurnal temperature range (DTR) is predominant during the dry season, as result showed a strong positive relationship between the parameters during the dry season and a low relationship during the wet season.