This study examines the day-time variations in the physiologic comfort of Nigeria using the effective temperature, temperature-humidity and relative strain indices (ETI, THI and RSI, respectively) for 59 years (1951-2009) at 20 well-distributed (2 by 2 °) meteorological stations across Nigeria. It also examines the responses from 3600 sample population from tertiary institutions across Nigeria. Results indicated thermal stress in Nigeria, and showed that both heat and cold stress varied temporally and spatially (1200 - 1500 Local Standard Time, LST as the most thermally uncomfortable period of the day, while before 0900 and around 2100 LST were more comfortable). The study showed that judgment on climate issues were often beclouded by religious or ignorant sentiments. Efficient coping strategies for thermal stress are generally lacking, being limited by poor education, financial capacity and inadequate government commitment to cater for the health effects of extreme climate conditions. The study concluded that Nigeria, which exemplifies many developing countries, is not yet prepared for the effect of future climate change. The study recommends climate education, improves health schemes for climate-related morbidity and improves greening of the urban environment.
Human concerns for thermal comfort are generally indisputable, especially with the recent increase in crave for habitat modification and environmental sustainability [
Information on thermal comfort is required for early warning against climate-related sickness, thermal stress and for planning for holidays, migration, tourism and building [
Recent studies on the thermal comfort in Nigeria showed that the Nigerian thermal climate may not be well explained by a single thermal index, and therefore suggested the need for a multi-indices approach [
Nigeria (4˚N - 14˚N and 3˚E - 15˚E) is in the southeastern edge of the West African region and covers about 14% of West Africa. Nigeria is characterized by dry and rainy seasons. While the dry season is accompanied by the Tropical Continental (cT) airmass influenced dust-laden (Harmattan) wind from the Sahara desert, the rainy season is heavily influenced by the Tropical Maritime (mT) from the Atlantic Ocean (
Areas surrounded by high elevation (especially in the north-central region) can be influenced by the relief rainfall. Studies have classified the Nigerian climate into (a) tropical rainforest climate, (b) tropical savanna climate and (c) highland climate or montane climate [
This study used day-time (0600-2100 Local Standard Time) relative humidity and temperature data for 20 meteorological stations to compute the selected thermal comfort indices. The thermal comfort indices have been used in previous studies, and have been found to be suitable to the Nigerian (and tropical) climate [
where
T is the mean temperature of the air (˚C), H is relative humidity [%), V is the saturation vapour pressure (in hPA), and is estimated as
An area is classified as thermally comfortable if its atmospheric condition is characterised by ETI values of 18.9˚C - 25.6˚C or THI values of 15˚C - 24˚C or RSI values of 0.1 - 0.2 (ratio, no unit). Cold stress occurs at
values below the minimum while the maximum threshold marks the beginning of a heat stress condition [
The preference and responses of Nigerians on thermal comfort was assessed by administering a set of questionnaire to about 200 randomly selected workers from each of purposively selected 18 tertiary (University, Polytechnic, or College of Education) locations in Nigeria (
Sample population =
A sample size of 200 was finally accepted because less than the targeted sample sizes for most institutions were returned. Almost 60% of the respondents worked indoor while 40% worked outdoor. Most of the respondents were adults between the ages of 18 and 60 years, who worked either on full or part time basis at the sample locations. The 18 - 60 years age group makes up the most productive set of the population. More than 70% of the respondents had lived in the sample location for at least 5 years and this gives the group an advantage of fair understanding of the climate of the sample location. More than 99% of the respondents had attained at least primary education status (and 67.5% have had tertiary or post-secondary education), suggesting that they would easily understand the content of the questionnaire and its purpose. At least, 40% of the workers claimed to make a minimum of five hundred thousand (500,000 Naira) per annum; an equivalent of about US$9 per day as at the time of the research.
The 59-year (1951-2009) average minimum, maximum and mean temperature in Nigeria (based on the selected 20 stations) is 21.4˚C, 32.8˚C and 27˚C, respectively. Minimum temperatures were generally below the overall mean in the tropical savanna (except at Sokoto and Yola) and montane regions while mean maximum temperature in all stations within the savanna was higher than its overall mean, except at Bauchi and Ilorin. The montane, Tropical Wet and Dry and Tropical Wet climate regions, however, had lower (than the overall average) mean maximum temperature. The mean relative humidity varied between 36.5% and 85.1%, with 62% as the mean. Variations in both temperature and relative humidity increased from south towards the north, except for few stations in the guinea and sudansavanna which exhibited higher variability than the sahel. Lowest mean annual ET occurred at the montane region (Jos, 19.4˚C) while the highest values occurred at Warri in the tropical wet climate (26.1˚C). Annual ET values at most of the stations within the Sudano-Sahelian (Bauchi, Katsina, Maiduguri, Nguru and Potiskum) and montane (Jos) climate regions are lower than the overall average (24.3˚C). Stations within the guinea savanna, and tropical rainforest on the other hand, exhibited higher ET than the overall average. Highest mean THI (26.3˚C) occurred in Lokoja (Guinea savanna) while the montane station exhibited the lowest (19.6˚C) mean THI. Highest RSI ratio (0.2) occurred at Warri in the Tropical wet climate while the montane region exhibited the smallest ratio (0.01) (
The different variability in the investigated parameters suggests that thermal comfort vary substantially across Nigeria, and the differences in the thermal indices also indicate that predicting the Nigerian climate based on a single index approach needs further study. Studies [
Climate Region | Meteorological Station | Temperature (˚C) | Relative Humidity (%) | ET (˚C) | THI (˚C) | RSI (ratio) | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Minimum | Maximum | Mean | |||||||||||||
M | SD | M | SD | M | SD | M | SD | M | SD | M | SD | M | SD | ||
Tropical Savanna (Sahel) | Nguru | 21.2 | 4.4 | 35.3 | 3.6 | 28.2 | 3.5 | 36.5 | 21.1 | 23.1 | 1.5 | 24.2 | 1.5 | 0.17 | 0.05 |
Tropical Savanna (Sudan) | Katsina | 19.4 | 4.3 | 33.7 | 3.4 | 26.5 | 3.5 | 38.9 | 23.5 | 22.5 | 0.6 | 23.3 | 0.6 | 0.13 | 0.02 |
Sokoto | 22.0 | 3.6 | 35.2 | 3.2 | 28.6 | 3.0 | 42.7 | 23.6 | 24.4 | 0.6 | 25.4 | 0.6 | 0.19 | 0.03 | |
Maiduguri | 20.1 | 4.6 | 35.3 | 3.6 | 27.7 | 3.6 | 39.9 | 20.7 | 23.5 | 0.6 | 24.4 | 0.6 | 0.16 | 0.02 | |
Potiskum | 19.7 | 4.5 | 34.4 | 3.3 | 27.0 | 3.4 | 39.5 | 23.9 | 22.4 | 1.3 | 23.3 | 1.2 | 0.13 | 0.10 | |
Yelwa | 21.3 | 3.6 | 34.1 | 3.0 | 27.7 | 2.3 | 60.7 | 19.1 | 24.9 | 0.5 | 25.5 | 0.7 | 0.18 | 0.06 | |
Bauchi | 19.0 | 3.5 | 32.7 | 2.8 | 25.8 | 2.6 | 46.7 | 23.1 | 22.4 | 0.7 | 23.1 | 0.7 | 0.09 | 0.10 | |
Yola | 21.7 | 3.2 | 34.7 | 3.1 | 28.2 | 2.4 | 55.2 | 23.5 | 24.9 | 0.9 | 25.7 | 0.9 | 0.21 | 0.05 | |
Montane | Jos | 16.0 | 2.3 | 27.6 | 2.3 | 21.8 | 1.7 | 50.0 | 25.9 | 19.4 | 0.3 | 19.6 | 0.4 | 0.01 | 0.01 |
Tropical Savanna (Guinea) | Bida | 22.8 | 1.8 | 33.7 | 2.8 | 28.3 | 1.9 | 64.4 | 18.1 | 25.5 | 0.8 | 26.1 | 0.6 | 0.21 | 0.06 |
Ilorin | 21.3 | 1.7 | 32.2 | 2.6 | 26.8 | 1.6 | 74.4 | 11.6 | 24.4 | 0.5 | 24.9 | 0.5 | 0.17 | 0.02 | |
Lokoja | 22.8 | 2.0 | 33.0 | 2.4 | 27.9 | 1.7 | 73.4 | 8.2 | 25.9 | 0.7 | 26.3 | 0.6 | 0.22 | 0.04 | |
Makurdi | 22.3 | 2.5 | 33.3 | 2.6 | 27.8 | 1.8 | 69.8 | 14.2 | 25.4 | 0.9 | 25.9 | 0.7 | 0.21 | 0.04 | |
Tropical Wet and Dry | Ikeja | 23.1 | 1.3 | 30.9 | 1.9 | 27.0 | 1.4 | 82.6 | 5.8 | 25.3 | 0.6 | 26.1 | 0.6 | 0.21 | 0.04 |
Benin | 23.0 | 0.8 | 31.3 | 2.0 | 27.1 | 1.4 | 83.9 | 5.7 | 25.9 | 0.6 | 26.1 | 0.6 | 0.21 | 0.04 | |
Calabar | 22.8 | 1.0 | 30.6 | 1.8 | 26.8 | 1.2 | 85.1 | 5.0 | 25.7 | 0.9 | 25.9 | 0.8 | 0.19 | 0.09 | |
Tropical Wet | Warri | 23.1 | 0.9 | 31.4 | 1.8 | 27.3 | 1.2 | 83.9 | 4.8 | 26.1 | 0.4 | 26.3 | 0.9 | 0.22 | 0.02 |
Port Harcourt | 22.4 | 1.2 | 31.1 | 1.8 | 26.7 | 1.1 | 83.4 | 5.5 | 25.6 | 0.4 | 24.8 | 2.1 | 0.20 | 0.03 | |
Overall mean | 21.4 | 3.4 | 32.8 | 3.4 | 27.0 | 2.8 | 62.0 | 24.8 | 24.1 | 0.9 | 24.8 | 1.8 | 0.20 | 0.18 |
index, and are generally not well suited for regional physiological or thermal analysis.
The generally lower minimum temperature in the savanna region (than in the tropical wet) indicates that the night-time temperature in this region can vary from cold stress to comfortable climate than obtained in the tropical wet regions while the relatively higher maximum temperature suggests day-time discomfort in the tropical savanna. Temperature can also vary as a result of urbanisation, commercialisation and industrialisation.
Most towns and cities in Nigeria are characterised by transport and commercial activities that are capable of increasing the immediate temperature and contribute to the global temperature [
Evaluated thermal indices (THI, ETI and RSI) showed temporal and spatial variations. Peak of the heat stress condition occurred at 1500 LST while the early morning time (before 0900 LST) was more conducive. The two years taken to explain the temporal variations (1971 to represent a typical cool year, and 2001 for a typical warm year), and the results of their moving average interpolations are presented as
the interpretations of the day-time thermal comfort for Nigeria (based on the selected stations) using ETI, THI and RSI vary with each of the indices. Thermal comfort in 1971 also exhibited slight difference from that of 2001, especially at 0900 LST and 2100 LST (
On the other hand, the results of the monthly variations of thermal comfort at selected settlements in Nigeria shows that spatial variations occur. The results of ETI and RSI were similar, and therefore only ETI and THI are presented. In both ETI and THI, Lokoja (in the guinea savanna) showed most day-time hours of heat stress (1100 - 1700 LST) while Jos (montane region) exhibited the least number of hours with day-time thermal stress condition. Calabar and Benin (tropical wet) exhibited heat stress in the afternoon (1200 - 1700 LST) in June-Oc- tober. Heat stress at the tropical wet regions occurred for more hours (1000 - 1700 LST) between November and April. The results of the monthly variations of THI for Lokoja and Jos exhibited different features; heat stress was indicated in Jos (February-April) while ETI and RSI reflected comfortable climate for same period. In other settlements, more hours exhibited heat stress with the THI map than shown with the ETI map (
In general, the results of this study indicated that 1200 - 1500 LST was the most thermally stressful in Nigeria. This is typical of the tropical region where the sun is known to be directly overhead at noon before the heat accumulates and peaks shortly after. Samendra and Ayesha [
urbanisation, gas flaring activities among others [
Whilst the perceptions of sampled Nigerians varied on the seasonal distributions of heat stress (p ≤ 0.05 for dry season, p ≥ 0.05 for Harmattan and rain season), about 50% from southern (tropical wet) and northern (savanna) regions described the dry season as generally warm and characterized by heat-related morbidity, including headache and heat rash. The Harmattan was described by most respondents (>70%) as dusty, windy and linked with dry eyes, dry skin and dry throat while the rainy season is generally cool (and in some cases, cold) and linked with severe cold, headache and cough. About 90% of the sample populations responded to heat stress condition mainly by alternating their modes of dresses (from thick to thin layered dress in dry season or vice versa in the rainy and Harmattan season. Majority (>64%) also cover their head and arms as response to the dusty Harmattan or severe cold in both Harmattan and rainy season). While alternating different dressing mode to cope with a prevailing weather is a practice worldwide (
level (the poor is defined here as those whose concern is primarily on feeding themselves and families) prefer to install air conditioners in their car, house and office (or at least in one of them) in the present study.
However, unlike the other regions which have mapped weather health-response plans [
This study has examined the thermal comfort in Nigeria and the responses to thermal stress. The two hypotheses suggested for the study (that Nigeria is thermally comfortable, and that available coping strategies are sufficient to cope with thermal stress) are rejected. The study showed that thermal stress will increase in Nigeria as urbanization, population and the global temperature increase (although the condition varies seasonally and spatially), and that climate education is largely low among Nigerians. Majority of the respondents lack indigenous approach, and they preferred no precautionary solution to cope with extreme climate other than “prayers”. The general perception of the respondents on climate issues was beclouded by religious or ignorant sentiments. The results of this investigation suggest that efficient coping strategies for thermal stress are generally lacking; being limited by poor education, financial capacity and inadequate government commitment to cater for the health effects of extreme climate conditions in poor communities (which incidentally comprises more than half of the Nigerian population [