IMPACTS OF LAND-USE LAND-COVER CHANGE ON AIR TEMPERATURE OVER SOUTHWEST NIGERIA

Abstract

The impacts of land-use land-cover change (LULCC) on air temperature is assessed over Southwest Nigeria using Landsat TM, ETM+, and TIRS/OLI of 1986, 2001 and 2014 imageries from the archives of United State Geological Survey (USGS) Earth Explorer; and air temperature (minimum and maximum) data for a thirty year period (1985-2014) obtained from the Climate Research Unit (CRU) of East Anglia University, UK. The data were analyzed spatio-temporally for the occurrences of abrupt changes in land use/cover and air temperature and the spatial and temporal trends were investigated. The land use/cover data acquired were classified using supervised classification as vegetations, open surfaces, built-ups and water bodies. Quantitative analysis on the LULCC and conversion matrix was carried out using Land Change Modeler (LCM). The air temperature data were interpolated using Inverse Distance Weight (IDW) interpolation algorithm while annual, seasonal and decadal anomalies were analyzed spatially. Statistical approach was deployed to determine the rate of change, coefficient of variations and significant changes of the temperature data. The estimated conversion LULCC classes were classified and overlain by minimum air temperature (ATmin) and maximum air temperature (ATmax) change to evaluate their corresponding value spatially and numerically. Results showed that the major land conversion over this region was vegetation being converted into built-ups at the rate of 4 366.68km2 (57%) during the first period (1986-2001) and open surfaces converted to built-ups at the rate of 8 721.97km2 (42.81%) during the second period (2001-2014). Analysis of air temperature showed an increasing trend in both ATmin and ATmax with an annual rate of change of 0.21 and 0.12 respectively. The statistical analysis revealed that there is more variation in the ATmin than ATmax, with the high coefficient of variation of 2.9% occurring during the dry season. The numerical analysis of the impact of LULC conversion on air temperature indicated that changes in ATmin and ATmax responds positively to changes in LULC, but the magnitude of change is more in ATmin mostly for vegetation converting into open surfaces and built-ups. Land conversion to vegetations and water bodies influence change in ATmin while conversion to open surfaces and built-ups influence change in both ATmin and ATmax but influence more changes in ATmax. Although, the increase in the air temperature observed in this study is not in the extreme that could pose danger to the ecosystems, there is a need to monitor these changes and encourage greening programs that can abate unforeseen future extremes and enhance environmental quality and stability of the ecosystems.