Meteorology and Climate Science

The fast urban expansion has led to the transformation of the natural landscape into anthropogenic surfaces. The city of Abeokuta, for instance, is located in a region experiencing rapid urbanization, which has produced a remarkable effect on the surface thermal response. This effect significantly influences urban internal microclimatology on a regional scale. In this study, the surface temperatures and land cover types retrieved from Landsat TM and ETM+ images of Abeokuta city for 1984, 2003, and 2014 were analyzed. A quantitative approach was used to assess surface urban heat islands through the relationships among surface temperature and land cover types. Results showed that impervious surface areas were found to be correlated positively with high temperatures. Conversely, vegetated areas and bare surfaces correlated positively with mid temperature zones. This study found that areas with increasing impervious surfaces will accelerate LST rise and consequently lead to increasing effect of surface urban heat islands. These findings pose a major challenge to urban planners. However, the study would help to quantify the impacts of different scenarios (e.g., vegetation loss to accommodate urban growth) on LST and consequently to devise appropriate policy measures.

Vegetation cover has acted as a source of carbon sinks and air purifier for a long period of time especially in developed cities thereby affecting the global climate change. The study was conducted to spatially estimate the Normalized Difference Vegetative Index (NDVI) which is a vegetation indicator for a period of 28 epoch years for Abuja from 1987 to 2014. The positive signatures of NDVI decrease from 2009 to 2014. Statistical analysis of the observed data samples at 95% confidence interval revealed that the changes observed in Year 2009 contributed most to the changes that was occurred in Year 2014.The modeled NDVI values for the year 2014 based on the regression analysis of the previous three years shows a significant agreement between the simulated values for year 2014 and the observed values. In general, there has been fast transformation of the vegetation cover to other land uses. The study reveals vegetation cover had reduced more significantly. It is also worthy to know that the model generated in this research can be used to predict future changes and trends in the vegetation cover. This will provide policy makers with useful information for the proper planning and design of the city and other capital cities over West Africa.

A B S T R A C T The study is aimed at investigating urban heat island over Abuja based on the relationship between land surface temperature estimated from Landsat 8 Thermal Infrared Sensor (TIRS) band and four vegetation indices from Landsat 8 Operational Land Imager (OLI) bands. The four vegetation indices considered are the Red Edge Normalized Difference Vegetation Index 705 (NDVI705), Modified Soil Adjusted Vegetation Index 2 (MSAVI2), Ratio Vegetation Index (RVI) and Normalized Difference Built-up Index (NDBI). A linear regression is generated to evaluate the correlation of Land Surface Temperature (LST) with the four vegetation indices. LST relationships with NDVI705 and MSAVI2 showed negative correlations and low correlation coefficients (R) values while the relationships with NDBI and RVI showed positive correlations with NDBI having R value of 0.84. Negative and near-negative values NDVI705 and MSAVI2 were observed on built up areas, water bodies and bare surfaces while highest values of RVI and NDBI were recorded on built up surfaces. The trend analysis of LST against different Land use Land cover (LULC) indicated that there is a decreasing trend of LST across the sample points from bare surfaces to water bodies with R of 0.83. Significant hot spots of high LST were recorded in built up areas and bare surfaces while significant cold spots were seen on vegetated surfaces. In general, the LST, hot spots and cold spots were shown to have been greatly influenced by the LULC of the area.

Land surface temperature is an important parameter in the surface energy balance as well as the interaction between the terrestrial ecosystem and the atmosphere. Specifically, the impacts of Land surface temperature at the local to regional scales on the terrestrial ecosystems are not straightforward but rather complex to warrant any generalizations. Subsequently, this has been investigated at small spatial, observable scales. However, extrapolating findings from such small scales to larger scales is confounded by the diversity of landuse landcover. However, for a big territory like Abuja, point measurement approaches from the land surface are too expensive and time consuming for continuous application at sufficient spatial density at the regional scale. These techniques produce measurements over small footprints (m 2) which are difficult to extrapolate to the regional scale, especially over heterogeneous land surfaces. The study was conducted to spatially estimate the Land Surface Temperature (LST) for a period of 27 epoch years for Abuja from 1987 to 2014. The variability of these retrieved LSTs has been investigated with respect to different heterogeneous surfaces determined from the Landsat visible and NIR channels. The emissivity per pixel is retrieved directly from satellite data and has been estimated as narrow band emissivity at the satellite sensor channel in order to have least error in the surface temperature estimation. 2014 has the highest mean LST with the value of 301.39 0 k while the year 1987 had the lowest mean LST with the value of 309.05 o k showing that LST rose by 7.66 o k from 1987 to 2014. This depicts that there has been significant change in the temperature of Abuja and this could also affect the thermal comfort and body metabolism of the locals residing in Abuja. The trend of LST for the period of study was observed to be an increasing trend. When projected to 2025, the trend still remains an increasing one. This could affect the thermal comfort of the citizens residing in Abuja and also this is an evidence of global warming in Abuja.