THE MICROCLIMATIC CHARACTERISTICS WITHIN THE URBAN CANOPY OF IBADAN

Abstract

This study analyses the spatial, diurnal and seasonal characteristics of some climatic parameters within the urban canopy of Ibadan. These climatic parameters are global radiation, surface albedo, net long wave radiation and latent and sensible fluxes of energy. The analysis is based on data collected on a daily basis (0600 - 1800 hrs. GMT) for one year at twenty stations located all ever the city. Furthermore, twenty-year data (1961-80) on the characteristics of maximum and minimum temperatures, relative humidity and rainfall are analysed with the aim of analysing the effect of urbanization on climate over that period. This study makes a departure from earlier studies which were concerned mainly with the rural/urban dichotomy ir climatic parameters by actually looking into the intra-urban pattern of the climatic parameters. In this regard the city surface was classified into six land use categories on the basis of their components of buildings, water, tarred roads, untarred roads, paved surfaces, bare ground, lawns and trees. The laud-uses identified are 'high density’ built-up areas, 'medium density' built-up areas, 'low density 'built-up areas, 'commercial' areas, 'open spaces’ and ’rural’ areas. These land-uses were used as the basis for setting up the climatic stations and explaining results of the variation in climatic parameters. Results of the investigation show that components of radiation and energy budgets vary considerably from the rural areas to the urban centre. Global radiation values for the different land-uses range between 0,62 and 0.64 ly min-1 in the rural surroundings to between 0,56 and 0.58 ly min-1 in the urban centre. This shows a decrease of about Albedo mean values range between 15% and 18% in the rural area to between 8% and 10% in the city centre. The net radiation at the urban centre is about 15% higher than that at the rural area; the mean values for the different land-use surfaces being between 0.200 and 0.215 ly. Min-1 in the rural area and between 0.225 and 0.245 ly. Min-1 in the urban centre. Net long wave radiation increases from between -0.21 and -0.22 ly. Min-1 in the rural area to between —0.18 and -0.19 ly min-1 in the urban centre, The Increase in the city centre over the rural area is by about Mean values of temperature urban 'heat island' vary between 1.0°C and 1.5°C, and 2.5°C and 3.0°C during the vet and harmattan periods respectively, The extreme value of temperature 'heat island' is as high as 11.7°C. The relative humidity in the urban centre is 6,3% lower than in the rural surroundings during the wet season and 24.3% lower than the harmattan season. From the temporal analysis of climatic data over a 20-year period, it is found that temperature has increased significantly over time. Maximum temperature increased by as much as 0o7°Co Rainfall increase over time has also been related to urban effects. All these confirm that urbanization is changing the climate of Ibadan, Finally, land-use components and climatic parameters are correlated and the relationships between them are found to be statistically significant at 5% level of significance.