SPATIO-TEMPORAL VARIATION OF URBAN HEAT ISLAND AND THERMAL COMFORT IN COASTAL AND SAHEL REGIONS OF NIGERIA

Abstract

Results of previous studies with respect to thermal conditions in the Northern and southern Nigeria differs therefore, there is need to examine which region is more thermally uncomfortable than the other using different approach. The Spatio-Temporal Variation of Urban Heat Island (UHI) and Thermal Comfort were assessed while mitigating effect of Green Parks was examined in the two extreme regions in Nigeria namely the Coastal and the Sahel regions. Ten years satellite data spanning 2009 - 2018 were used for the analysis. Data used include air temperature, relative humidity, wind velocity, cloud cover and global radiation obtained from the archive of Era-interim reanalysis while Landsat imageries of the Green Parks were obtained from the United State Geological Survey satellite (USGS). In the Coastal region Oja-Oba, Effurun and Bogoberi are the urban locations while Akure Airport, Warri Old Airpot and Bogoberi rural neighborhood are the rural locations. Similarly, Sokoto Central District (SCD), Gwamaja in kano and Maiduguri Central Metropolis (MCM) are the urban locations while Sokoto Airport, Kano Outskirt and Dalakaleri are the rural locations. Ade Super Neighborhood Park, Tyga Villa Neighborhood Park and Botanical Garden are the three Green Parks in the Coastal region while Hospital road, Kano Zoo and Maiduguri Abattoir Neighborhood Park (MANP) are the green parks in the Sahel region. Urban, rural and Green Parks were classified using Stewart classification of surface characteristics. Urban Heat Island temperature difference relation was used to estimate UHI magnitude while three thermal indices-Predicted Mean Vote (PMV), Physiological Equivalent Temperature (PET) and Standard Effective Temperature (SET) were applied to assess the thermal conditions in both regions. The result showed that urban heat island occurred year round in both Sahel and Coastal regions. The Maximum and Minimum UHI are 0.670C and 0.580C and 1.260C and 0.690C in the Coastal and Sahel region respectively. Highest UHI magnitude of 1.260C occurred in Dalakaleri, Sahel region while least magnitude of 0.580C occurred in Effurun, Coastal region. The Mean and Standard Deviation (SDEV) stands at 0.620C and 0.050C and 0.850C and 0.160C in Coastal and Sahel region respectively. Seasonal variation showed that UHI attained its maximum and minimum values in dry season and Wet season respectively in the coastal region however, the contrary was the case with the Sahel region. All thermal indices used showed similar annual and seasonal trend. Most uncomfortable periods coincides with the transition from dry season to wet season in both regions while relatively comfortable period were associated with August break period in the coastal region and Harmattan dust haze in the Sahel. The Maximum and Minimum values of all the indices namely PMV, PET and SET are 2.55oC and -0.77oC, 33.27oC and 16.27oC and 30.49oC and 16.38oC respectively. Most uncomfortable thermal conditions occurred in the Sahel region as annual comfort level performance stood at 44% as against 56% in the coastal region. Surface temperature reduction across the buffer zones ranged between 1-7oC. There existed a statistically significant difference in the UHI and thermal sensation magnitude between both regions, as P-value <0.05 at 95% confidence level. The Sahel region is therefore more thermally uncomfortable than the Coastal region.