SPATIAL AND TEMPORAL VARIATIONS IN THE PHYSIOLOGIC CLIMATES OF NIGERIA (1951-2009)

Abstract

Few studies carried out on physiologic climatology (a study of average physio-thermal conditions of a place at a specific time) of the tropics emphasised variations in thermal conditions of tropical Africa. There is no consensus on the most suitable index of physiologic comfort despite increasing vulnerability to extreme climate conditions. This study was therefore designed to examine the spatio-temporal variations in the physiologic climates of Nigeria between 1951 and 2009, peoples’ perception on physiologic comfort and adaptive strategies.

The human-biometeorological assessment model provided the conceptual framework. Archival data from 1951-2009 on temperature and relative humidity were collected from 18 meteorological stations, distributed over the different climatic sub-regions of Nigeria (12 in the tropical savannah, two in tropical wet, three in tropical wet and dry, and one in the montane). Physiologic comfort indices: Effective Temperature Index (ETI), Temperature-Humidity Index (THI) and Relative Strain Index (RSI) were computed using standard formulae. Periodic (1951-1980 and 1981-2009), decadal, seasonal, monthly and hourly variations in these indices were computed. Perceptions of physiologic stress among Nigerians were obtained with a semi-structured questionnaire, administered to 3600 respondents from the 18 locations (200 from purposively selected population at each location). Periodic variations were tested using ANOVA while trend in physiologic stress at each station was determined with linear regression. Data on temperature, relative humidity and questionnaire were analysed using descriptive statistics. Moving average technique in geographic information system was used to assess spatial variations. Data were analysed at p=0.05.

Among the sub-regions considered, sudano-sahelian savannah region exhibited minimum temperature range of 19.4-21.7oC. This region has maximum temperature (>32oC) higher than the tropical wet region and a relative humidity of ≤60.7%. Mean ETI, THI and RSI were 24.3±1.7oC, 24.8±0.8oC and 0.2±0.05 (ratio), respectively. Most stations, except in the guinea savannah, exhibited significant variations in the physiologic climates between 1951-1980 and 1981-2009. Decadal means of the indices showed increasing thermal stress (b≥0.01 at R2≥0.9). The sudano-sahelian climate exhibited heat stress (>25.6oC ETI, >24oC THI and >0.2 RSI ratio) condition in the dry season and cold stress (<18.9oC ETI, <15oC THI and <0.1 RSI ratio) in the harmattan while the tropical wet climate exhibited heat stress in both rainy season and harmattan. Heat stress occurred in the tropical rainforest and tropical savannah climates in March-April and April-May respectively. Cold stress occurred before 0800-hour and after 1800-hour in the montane and the sudano-sahelian savannah while heat stress occurred at 1200-1600 hours in all but the montane region. Linear regression indicated that heat stress has increased over time (b≤0.02). Spatial analysis indicated 2oC increase in heat stress between 1951 and 2009 across the regions. Eighty-five percent of the respondents perceived that heat stress increased their desire for conditioned indoor air, and 70.0% adapted to physiologic stress by alternating dressing modes. Physiologic climate, peoples’ perceptions and adaptive strategies varied spatially and temporally in Nigeria. Effective Temperature Index, Temperature-Humidity Index and Relative Strain Index were not similar because of their differences in temperature-relative humidity relationship.

Keywords: Physiologic climates of Nigeria, Physiologic Comfort index, Human- biometeorological assessment, Spatio-temporal variations

Word count: 496