Geo-Spatial Heat Index and Comfort Analysis of Port Harcourt City: An Approach to Environmental Health Care Delivery

This research examined the geo-spatial heat index and comfort analysis of Port Harcourt city as an approach to environmental health care delivery. Temperature data were generated from different land use types across days of the week in both wet (April to September) and dry (October to March) seasons. Heat index was derived when air temperature and dew point temperature of the locations were corresponded in the heat index chart or data logger calculator. Findings indicate that the city had experienced danger levels of discomfort above 41oC in the late dry season of January, February and March showing that heat cramps and heat exhaustion as well as heat stroke were probably to occur with continued activity of a person. On the other hand, early dry season of October, November and December had the best human comfort period of < 26.7oC temperature except Thursday and Friday with caution level of 27 to 32°C in the city of Port Harcourt; though fatigue was possible as prolonged exposure could result to heat cramps. High residential/commercial and administrative/industrial land uses had the highest human discomfort indicating that those living in these land use types would suffer extreme hazard of heat stroke. However, recreation and rural sites were the most comfortable land use types. Young children and old people are generally in more danger to the heat effects as the city has exceeded the 27oC thermal comfort threshold. It is therefore recommended that city planners and development practitioners should implement urban green policy of tree planting with special attention to residential/commercial and administrative/industrial areas without further delay in order to cushion the deadly menace of urban heat in Port Harcourt city and its environs.


Introduction
One of the greatest challenges facing cities across the world is rising temperature due to modification of biophysical components of the city surface areas by urban fabrics (Coseo and Larsen, 2014). The alteration of urban surface areas has resulted to the concept of Urban Heat Island (UHI). UHI occurs when temperature in a city rises above that of the extended rural outskirts in the urban canopy (Yow, 2007). This temperature rise is as a result of rapid population and urbanization with the attendant UHI effect that is making several cities become very uncomfortable to live due to its impact on Heat Index (HI) and economy (Stewart, 2011;Stone, 2012). Heat Index also known as humiture is an index that associates air temperature and dew point temperature or relative humidity of shaded areas to suggest human perceived corresponding temperature on how hot people would feel if the dew point temperature or humidity values vary in shaded areas (Brooke, Michelle and Roger, 2013). Heat index is the apparent temperature which measures how hot it really feels when dew point temperature or relative humidity is factored with the actual air temperature. This temperature is known to be the felt air temperature, apparent temperature and real feel of temperature of the environment. The heat index expresses the level of comfort or stress provided by a given area (Ketterer and Matzarakis, 2014).
Air temperature is a measure of how hot or cold the air is at a given time; and relative humidity is a measure of the amount of water (moisture) in the air as compared to the maximum amount of water the air can absorb usually expressed in percentage. When air cannot absorb any more moisture, it is said to be fully saturated; it means that its relative humidity is 100 percent (Tawhida and Hisham, 2013). On the other hand, dew point is the temperature at which a given volume of air at certain atmospheric pressure is saturated with water vapor, causing condensation and the formation of dew, which is the condensed water seen on flowers and grasses early in the morning. Furthermore, the higher the relative humidity, the closer the dew point to the current air temperature. When dew point is below freezing (0°C or 32°F), the water vapor turns directly into frost rather than dew (Sarah, Lee, Kate, Phong, Lan and Phuong, 2016). Thus, Harlan, Brazel, Prashad, Stefanov and Larsen (2006) concluded that dew point temperature and humidity are key variables that influence thermal comfort of a city; and they are prospective tools in weather forecast used to express the amount of moisture in the air.
Generally, when the ambient air temperature is above the comfort threshold, it will result to heat cramp, respiratory problems, heat stroke and eventual death as well as loss of economic growth (Nwaerema, Ologunorisa, Nwagbara and Ojeh, 2019;World Health Organization [WHO] 2007). High temperature can impair quality of water bodies which could result to the death of aquatic life and food shortages (United States Environmental Protection Agency [USEPA] (2007). In addition, the demand for energy will continuously increase with rise in UHI and accelerated heat index. For instance 0.6 o C rise in temperature will result to 2% energy demand and 10% of global energy demand is used to compensate for heat island (James, 2002 Temperature, humidity, intensity of wind speed as well as type of clothing affects level of comfort of city dwellers. The type of physical activities engaged by a person under a given environmental condition will influence the stress and comfort level. Many scientists have carried out biometeorology of the environment over the years with a welldeveloped heat and stress indices for human comfort (Sushil, Sagnik, Popat, Mamta, Vaishali, Sourangsu and Rohit, 2017).
However, daily anthropogenic activities have caused urban heat budget variation in Port Harcourt space. Climatic parameters vary from season to season and across different local climatic zones. Different land use types have their identical homogenous biophysical characteristics of urban pavement materials and vegetal cover as well as water bodies. Wind speed varies across the canopy layer according to the urban relief system resulting to variation in the city energy distribution. In the same vein, temperature spread has effect on the heat index in seasons and days of the week. Accordingly, it becomes expedient to investigate the geo-spatial variation of heat index with the trend of mass movement of people and alteration of biophysical space of Port Harcourt metropolis and environs.

Method
Port Harcourt is a coastal settlement located in the Niger Delta region of Nigeria with Latitudes of 4 º 05'30''N and 5 º 14'25''N and Longitudes 5 º 40'30''E and 7 º 11'01''E Greenwich Meridian (Figure 1). The soil is dominated with sedimentary formation. As a coastal city close to the Atlantic Ocean, the atmospheric characteristics are influenced by the monsoon climate. The wind flow system is derived from the marine and land breezes to the inland city (Nwaerema, Ojeh, Amadou and Atuma, 2019). At continental scale Port Harcourt climate is modified by the continental air mass from the north-easterly winds in the Inter-Tropical Convergence Zone (ITCZ). Rainfall volume ranges between 2000mm to 2500mm favoring the months of April to October (Chiadikobi Omoboriowo, Chiaghanam, Opatola, and Oyebanji, 2011). Relative humidity rises from April to September with peaks in July and a sharp drop in January to March (Nwaerema and Nwagbara, 2018). Port Harcourt experiences high temperature from January till March; within this period relative humidity is low. Temperature up to 32°C is common during the dry season and lowest of 26°C is noticeable in July (Edokpa and Nwagbara, 2017). Annual humidity value is 85% in the wet season and cloud cover is 6 oktas during the wet season with low trend in the dry season Chiadikobi, 2017). Mean wind speed is between 0-3m/s capable of influencing urban heat and weak wind speed will accelerate thermal discomfort of the city especially during nocturnal hours (Shaibu and Utang, 2013;Nwaerema and Nwagbara, 2018;Nwaerema and Edokpa, 2019). Heat index is characterized by coastal climatic conditions as they impact on human comfort and health.

Figure 1. Port Harcourt Metropolis and Environs
Temperature and dew point temperature data as the key drivers of heat index were measured and computed for 12 months in wet and dry seasons: April, May and June (AMJ, as early wet season), July, August and September (JAS, as late wet season), October, November, and December (OND, as early dry season) and January, February and March (JFM, as late dry season) in 2017/2018 at 0006 (Morning), 1200 (Afternoon) and 1800 (Evening) hours accordingly. The data sets were organized according to daily averages in days of the week in wet and dry months. Temperature data were observed using LCD Digital Multi-Thermometer Loggers placed in delineated land surfaces (35 sample points) on the selected hours in the days of the week in wet and dry seasons ( Figure 2). Field assistants from private homes and business areas took the measurements simultaneously. The thermometers were Handheld Digital devices with ST9269 model and St-9283B/St-9269B, factory-made by MEXTECH. Resolutions were of 0.1 0 C (0.2 0 F) with measuring range of -500C to 3000C (-580F -5720F) at St-9283B and -500C to 2000C (-580F -3720F) at St-9269B respectively. The accuracy constant was ±10C, ranging -500C to 1500C (±20F in the range of -220F to 3020F). Error readings were very minimal as measurements were approximately at the height of a head, 1.5 meter above the ground in the canopy layer. Homogenous purposive sampling technique was adopted based on homogeneity and shared characteristic of delineated land categories. Finally heat index was derived when air temperature and dew point temperature of the locations were corresponded in the heat index chart or data logger calculator (Table 2). Heat index was also derived by computing air temperature and relative humidity using the heat index chart or data logger calculator. The computation of heat index is obtained by multiple regression analysis programmed in the calculator and the data logger (Brooke, Michelle and Roger, 2013; National Centre for Environmental Prediction [NCEP], 2018; Anderson and Peng, 2012).
The dew point temperature (Td) was derived using the dew point calculator, by keying the temperature data, the dew point calculator associates and estimates temperature for which air must be cool at a given temperature reading (Calculator.net, 2018;Dpcalc.org, 2018). Dew point is closely related with relative humidity, one of them can be used along with air temperature to estimate heat index of an area (Mark, 2005). Also, temperature in degree Celsius ( o C) was converted to degree Fahrenheit ( o F) [(0 o C x 9/5) + 32 = 32 o C] and applied in the Heat Index (HI) chart (Table 2) as the standard humiture table for heat index studies. The temperatures in Celsius were converted to Fahrenheit to correspond to the standard humiture in Fahrenheit for consistency and accuracy as well as better analysis of results. The humiture is already existing standard reference table for heat index studies provided by heat index experts used for humiture analysis. Temperature effects of heat index were corresponded to the various temperature readings of caution, extreme caution, danger and extreme danger in the analysis (Table 3).
Heat index is the apparent temperature which measures how hot it really feels when dew point temperature or relative humidity is factored with the actual air temperature. This temperature is known to be the felt air temperature, apparent temperature and real feel of temperature of the environment. The heat index expresses the level of comfort or stress provided by a given area.
While perception varies among people, some people at some level can acclimatize to high dew points while high dew points are generally uncomfortable because the humidity inhibits proper evaporation of sweat, making it more difficult for a person's body to cool. Conversely, lower dew points can also be uncomfortable, causing skin irritation and cracking as well as drying out a person's airways. It is recommended that outdoor temperatures be maintained

Results
During the early wet season of April, May and June (Table 4), 75% of the period was within heat index caution level (27-32°C) and 24.3% (32-41°C) under extreme caution level indicating that heat cramps and heat exhaustion were possible. It showed that continuing activities could result to heat stroke especially those located in mixed residential/commercial, administrative/industrial and medium residential areas respectively. On the average, all land use types had caution level heat index except residential/commercial land use with extreme caution level. Residents in educational, recreational and rural sites had better comfort level with less heat hazard. Also, beginning of the week such as Monday, Tuesday and Wednesday had severe effect of the urban heat index. Differences in temperatures across days of the week and land use types is as a result of variations in anthropogenic activities across days of the week and mixed distribution of vegetation, water bodies, urban fabrics and climatic parameters across the various land use types. The heat index during this period was unlikely compared to the high heat index of Porto in July 2006 which recorded excess of 107 deaths at 52% increment characterized by very high temperatures of 29ºC to 37ºC and relative humidity of 42% to 71% (Monteiro, Carvalho, Velho and Sousa, 2011). Author, 2018.
In the late wet season of July, August and September (Table 5), 75% of the period was within heat index caution level (27-32°C), 17.1% (32-41°C) under extreme caution level and 5.7% (< 26.7 o C) was under comfort threshold indicating that heat cramps and heat exhaustion were possible. The late wet season was relatively cooler than the early wet season. However, the period showed that continuing activities could result to heat stroke especially those located in mixed residential/commercial, administrative/industrial and educational sites. On the average, all land use types were under caution level heat index during the period. Residents in educational, recreational, high residential and administrative/industrial areas experienced some form of comfort on Mondays and Thursdays during the period. Generally the period exceeded the comfort threshold except few days of the week. Studies conducted by Ponni and Baskar (2015) and Ana, Vania, Sara and Carlos, (2013) on apparent temperature in daily mortality verified that during a hot season when the comfort level is exceeded the increase of 1ºC in daily average apparent temperature will result to the increase of 2.7% in respiratory causes for mortality. Author, 2018 Early dry season (October, November and December) ( Table 6) was the coolest period of the year with relatively comfortable heat index level. All days of the week experienced relative comfort (< 26.7 o C) except Thursday and Friday with caution level of (27-32°C) expressing the view that heat cramp and fatigue were possible with extended exposure to heat. Greater part of land uses had good comfort threshold except administrative/industrial, high residential, residential/commercial and medium residential areas. On the average, recreational and rural areas maintained moderate comfort threshold throughout the period. Monday, Tuesday and Wednesday had relatively better comfort heat index level during the season. Recreational land use had the best heat index level during the period. There was absence of extreme caution heat index level during this season indicating that the people in the area had lesser heat cramps, exhaustion and heat stroke due to the present of the harmattan season. The climate location and air velocity influence level of thermal comfort of a place. However, studies have established proposed operative temperatures and wind velocities ranging from 0.4m/s for 24-27 o C, 0.41-0.8 m/s for 27-29 o C, and 0.81 m/s for 29-31 ˚C for human comfort in the country considering the influence of wind velocity on thermal performance (Ana et al, 2013;Almeida, Casimiro andCalheiros, 2010, Candido, deDear andLamberts, 2011). In this vein, the harmatan season accelerates wind velocity in this period thereby moderating the thermal performance of Port Harcourt city for human comfort.  (Ronald, William and Harry, 2010;Khaled, 2011;Edokpa and Nwaerema, 2019).

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and typically sweating less than adults. Also, children are often less aware than adults of the need to rest and rehydrate. Thirst is a late sign of dehydration, and it is important to remain hydrated, particularly before, during and after outdoor activities, especially those involving heavy physical exertion. In addition to children, people with certain conditions including, the elderly, obesity, diabetes, heart disease, cystic fibrosis and mental retardation are at greater risk of overheating and dehydration (Ana et al, 2013

Discussion
This study significantly demonstrates the geo-spatial heat index and human comfort analysis of Port Harcourt city as good approach to environmental health care delivery. The results ascertained that high residential/commercial and administrative/industrial areas of the city were more vulnerable to severe health hazards as they have greatly exceeded the human comfort threshold of 27 o C indicating that those living in these sections of the city would relatively suffer more of exhaustion, fatigue and heat stroke. The findings showed that dangerous heat index (>41 o C) were common in the late dry season of January, February and March with possible greater heat hazards on children and elderly. Heat stress is a condition that the body cannot cool down properly through sweating which results to rising body temperature and may damage the brain and other important organs. Heat stress can cause dehydration which is a big risk to adults and children. Symptoms of heat stress include hot and dry skin, paleness, rapid heart rate, muscle cramps, nausea and vomiting, disorientation and confusion, delirium, fainting or coma, worsening of pre-existing medical conditions. Children's body surface area makes up a much greater proportion of their overall weight than adults; therefore they suffer dehydration at 2% loss of body water. The elderly at 65 years and above are vulnerable to heat related illness due to their weak body organs and inability to adapt to heat stress as well as their already existing ailments accompanying old age. Thus, rural and recreational sites had relatively possible thermal performance due to their unique vegetal cover and water bodies. It is recommended that city planners and development practitioners should implement urban greening policy of tree planting and proactive management of residential/commercial and administrative/industrial areas without further delay in order to cushion the deadly menace of urban heat stress in Port Harcourt city, Nigeria.