GIS in the Assessment of the Impact of Microclimatic Variables on Human Comfort in Akure, Nigeria

This study involved the use of Geographic Information System (GIS) to examine variation of physiologic comfort of the people living in Akure urban environment using physiological equivalent temperature (PET) index. PET value generated from both micro-climatic parameters and thermophysiological data measured, using Rayman model because of its ability to generate mean radiant temperature and PET which is useful in thermo-physiological heat balance model. It also examines the responses from sampled population across the land uses. Results showed that thermal heat stress are found spatially and temporally (6:00; 12:00 and 18:00 local standard time, LST) within the study area as high as (41-55) °C due to different activities in each of the land uses. Results indicated that many of the respondents are yet to have better understanding about thermal stress and it effects. The recommendation from this study is that more days of data should be measured during dry season, and planting of tress and urban greenery should be strongly encouraged as a means to improve the micro climate as well as the level of human comfort in Akure, Nigeria.


Introduction
The effect of the climatic variability can be seen on human well-being, health and environment (Adakayi, 2009) which makes the comfort of human as a phenomenon both spatial and temporal. The most important climate of any urban environment is microclimatic conditions, which differ significantly from that of rural areas. Micro-climate can be described as the climate at small spatial and temporal scales of any biological environment (Shaibu and Utang, 2013). Ndetto and Matzarakis (2013) suggested that better understanding of urban microclimate and bioclimatic condition of any city requires urgent attention today, as a result of the constraints by urbanization and global climate change. Studies show that the world is experiencing rapid urbanisation, with 45% of all the population already living in urban areas as of year 2000 (Arnfield 2003). Urban is defined as an environment where the density of population and economic activities are more than in other places with higher rate of destruction of natural resources (Toy et al., 2007).
Evidence has shown that anthropogenic heat emission at various land use is a major factor contributing to heat island (Ohashi et al., 2007). With higher rate of economic development, urbanization coupled with population growth continue in developing countries, anthropogenic heat increases as well (Ichinose and Bai, 2000). Akure is not exempted from this as the population and economic activities have increased and more than tripled from 1990-2006 (Ogunsote, 2007;Balogun et al., 2011). There is mutual relationship between man and climate that man responds to variation in climate by insulating buildings, heating and air-conditioning. The aim of any man is to be comfortable despite the climate, and this gives rise to the belief of thermal comfort (Eludoyin et al., 2013). Outside comfort zone lies the thermal stress (Ogunsote and Prucnal-Ogunsote, 2007). Thermal comfort can be expressed with the six basic parameters, two of these parameters are personal parameters (cloth and activity levels) and the others are environmental parameters (air temperature, wind speed, relative humidity and mean radiant temperature) .
During the last decade, interest in the assessment of urban thermal comfort has increased because of climate changes and increased heat stress in cities. But there have been relatively small numbers of studies on thermal comfort for outdoor environment (Swaid et al., 1993;Nikolopoulou et al., 2001;Givoni et al., 2003;Spagnolo & de Dear 2003). A good number of indices have been developed to accurately estimate thermal comfort in urban environment. Indices such as standard Effective Temperatures (SET), Predicted Mean Vote (PMV) and physiological equivalent temperature (PET) are the most broadly used as outdoor comfort indices (Givoni et al., 2003). However, for this study PET will be considered because of its ability to care for the diversity of outdoor climatic settings; it will be implemented using RayMan model which include the inputs of meteorological parameters with thermo-physiological parameters which are; human activity level and cloth value .
By utilizing and implementing GIS mapping techniques, changes in urban thermal comfort can be monitored and mapped for developmental projects (Rahman et al., 2009), as the Urban and regional planners are demanding easily understandable methods to facilitate comfortable urban microclimates.
The importance of this paper lies in examining the human comfort of people in Akure, a city in Nigeria, based on bioclimatic and urban climate studies of the area, demonstrating the quantitative evaluation of human comfort and heat stress within the study area by the measurement of microclimate parameters. Climatically, Ondo state has humid tropical climate and belongs to the equatorial rain forest belts.
The climate of the study area is classified as tropical wet and dry season. Characteristically, wet season ranges between April to October and dry season ranges between November and March. Akure maintains moderately warm humid tropical climate with high temperature, maximum temperature of about 86°F and minimum stand at about 71.6°F with an average daily temperature of 93.2°F. Rainfall is averagely about 1524mm per year (Ogunsote, 2007).

Kestrel weather Meter 3000
A physical measurement of micro-climatic parameters that influences human energy balance was carried out. The parameters were measured using a hand-held weather meter instrument by Kestrel "3000" series with Global Positioning system (Garmin GPS etrex 30) of ± 2.0 meter used to record coordinate of the points at the height 1.1m above ground level. The instrument was calibrated and tested with the following specifications; Temperature measurement range -29 °C -70 °C with the accuracy of ±0.5 °C, Relative humidity measurement range 5% -95% with accuracy; ± 3.0 and Wind speed measurement range 0.6-40.0 m/s, with accuracy of ± 0.1.
All the field surveys were performed on days of dry season of the year, In order to account for change in daily climatic conditions, the field survey was conducted in three sections a day (morning (6:00), midday (12:00) and evening (18:00) local time) for five days in different delineated land use types as shown in figure 2: and the average of each section were obtained as shown in table 2 below.
Data collection was based on participatory approach in a field survey. Olanipekun (2014) argued that field surveys are the only way through which comfort standards can be realistically related to people's needs among acclimatized populations. This is to say that the people in the field survey will act as "meters" of their environment. Different site was visited to obtain different perspective view of the people concerning outdoor human thermal comfort in Akure urban area such as commercial, institutional (tertiary), residential, and administrative area among others. Composite sampling method was thus adopted by taking the readings in different days at the same points.  (Edward & Johnny, 2015) was used: Where equals number of samples, equals total population targeted and e equals error margin.
Slovin's formula is usually used when there is no knowledge about the total population of the study area. A total of 1000 population were targeted at the margin error of 6.3% at the confidence level of 93.7%. Studies shows that the responses from a tertiary institution could sometimes be stronger than that of any other area in an urban settlement with the probability that those in schools are likely to be more conscious and inquisitive than others within any study community (Eludoyin, 2014).
The participatory assessment was based on responses to a questionnaire survey, which was administered simultaneously with physical measurement during each survey. The scope of the questionnaire was based on several preceding studies, and conformed to ASHRAE standard questionnaire for indoor thermal comfort study (ASHRAE, 2010  The spatial distribution of the generated PET values in the different land use types was then visualized. The Physiologically Equivalent Temperature (PET) was adopted for this study because of its appropriateness to the law that govern the thermal comfort and inclusion of both meteorological and non-meteorological parameters in its calculation by the Ryman model .

Figure 4: Methodology Flow Diagram
Respondents who were sitting and standing with low physical activities were included during the survey, the metabolic rate was taken to be 1.2 met and 1.4 met using ASHRAE, 2010 standard for sitting and standing respondents respectively (1 met=58.15W/m 2 ) according to "cloth value" during the study period which was rated as 0.66clo as a result of the season. The average values of data directly observed from the field were processed in Rayman model to generate PET values, which was integrated into geo-database as shown in Figure 4 above. Kriging interpolation method (Geostatistical analysis) was used, being the best interpolation technique for temperature as proved by literature (Gulyás and Matzarakis, 2007). Interpolated values classified were compared to match the PET index value for Nigeria Climate (Omonijo and Matzarakis, 2011).  sections, which was also observed in the noon and evening survey section. From table 2, the minimum, maximum and mean relative humidity for the whole study was given as 53.82%, 88.27% and 67.35% respectively. The speed of the wind recorded directly was 0.71m/s minimum value, 0.78 maximum value and mean value of 0.76m/s respectively. In general, the standard deviation for the measured parameters are low, this indicates that the parameters measured were homogeneous and uniform during the study period.  The map in Figure 6 represents mean daily (noon) value of PET based on the parameters of air temperature, relative humidity, wind speed, activities and cloth value. During the period of study, the thermal comfort condition (35°C -55°C) were observed at the hour of 12:00hr. The legend showed that the thermal environment during the study period of the hour was above extreme heat stress, with the concentration of the stress found in high residential area of the urban centre.   (2014), also obervsed heat stress in their study on Urban heat island and bioclimatological conditions in a hot humid tropical city in Akure, has more very hot and torrid afternoon. when most of the people feel discomfort, where urban heat island has its maximum occurrence at night between 18:00 and 22:00 local time despite the fact that thermohydrometric index (humidex index) was used.

Conclusion and Recommendation
High rate of heat stress has effect on the environment and on the health of people thereby leading to heat related diseases such as fatigue, sunstroke, muscle cramps, heat stroke and heat exhaustion. The result from this study showed that in general Akure is rather uncomfortable, providing useful information for planners and decision makers in planning new urban environment.
Futher studies is recommended in the area of similar surveys to be carried out during the dry season of the year. Also adequate awareness of heat stress and it related problem should be made known to people in Akure. Urban greenery and planting of tress within the city space is strongly recommended for Akure, Nigeria.