ASSESSMENT OF THE BIOCLIMATIC CONDITIONS OVER SOME SELECTED STATIONS IN NIGERIA

Abstract

Human bioclimatic studies have relevance in various aspects of the human life and the basic functions of the human metabolism are affected by several environmental factors of which climate is a major one. This study seeks to assess the bioclimatic conditions of some selected stations in Nigeria from 1981 to 2010. The specific objectives were to analyze the spatio-temporal variability of the key weather parameters critical to bioclimatic conditions, compute the bioclimatic indices for each station, evaluate the seasonal and decadal variation on the bioclimatic indices and analyze the spatio-temporal variation of the indices over the area. The stations used were selected to represent the climatic zone of Nigeria based on the three zones; guinea, savannah and sahel zones. The data used for this work was retrieved from the data archive of the Nigerian Meteorological Agency (NIMET) for 0600 and 1500 Local Standard Time (LST). The study applied the use of two bioclimatic indices namely; Physiological Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI). PET was computed using the Rayman model while UTCI was computed using the Bioklima model. The monthly variation of PET and UTCI revealed higher values during the dry months of the year and lower values in the wet months of the year. This indicated the periods of higher thermal stress levels in the dry months while the wet months were characterized with lower thermal stress levels. The spatial variations of both PET and UTCI was done for two different periods; dry season, and wet season, both indices also revealed differing distribution between the conditions at dry period and that of wet period. During the dry period, the northern part was cooler than the southern part, indicating less thermal stress at the northern part for 0600(LST) and 1500(LST). However, during the wet period, the majority of the northern region was warmer than the southern part at 1500(LST), indicating increased and higher thermal stress levels during this period. There was distinct variation in the bioclimatic conditions between both time periods at different seasons. The spatial variation of thermal indices over the study period were categorized into three decade; 1981 – 1990 (first decade), 1991 – 2000 (second decade) and 2001 – 2010 (third decade). Both indices revealed similar decadal variation at 0600(LST) and 1500(LST). The highest values of PET and UTCI at 0600(LST) in the second decade were higher than the first and the third decade, while the third decade had higher PET and UTCI values than the first and third decade. The spatial variation of both indices also revealed similar distribution across the stations. The seasonal mean PET and UTCI were also derived for the zones indicating the prevailing conditions per season. The condition at 0600(SLT) during all the seasons clearly showed that the stress level at guinea was the highest, followed by Sudan and then the Sahel zone. At 1500(LST), the conditions changed during the seasons. Sudan zone was the most stressed at dry, early-wet and early-dry seasons. The condition during the wet season was also different, as Sahel zone was the most thermally stressed zone. Although conditions during the wet season became less stressful compared to the other seasons, Sahel region maintained slight heat stress and moderate heat stress conditions according to PET and UTCI respectively