In both developed and developed countries, cities have been growing at a considerable rate. The high growth rate of these urban centers creates a necessity of creation of more land space to put buildings and infrastructures which in turn have resulted at cultivation of land thus messing up with the natural vegetation covering to it being replaced by manmade features. The overall effect of this development of cities is the alteration of the local climatic conditions resulting in a phenomenon known as Urban Heat Island (UHT). To understand this (effect of urbanization on the local climate of cities) a case study of Erbil city was suggest
For this study to be successful, two sets of data were used that is, ground weather station which made use of maximum and minimum air temperature recordings collected over specified duration of time and satellite images of the city. After an analysis of the two set of data was made a clear indication showed a significant change in the temperatures of the city as it was compared with that of the rural areas (ground weather station) (UHI) (Oke, 1987). On the other hand, satellite images were used to develop NDVI (normalized difference vegetation index) map of the city
Through a literature review conducted by the researcher, there were clear indication that notable changes were observed in the nature of atmosphere and vegetation covering the region. These changes are attributed to urbanization. This is because urbanization has caused the human to mess with the natural vegetation covering of the region. To expound on this it should be noted that vegetation cover of an area has a direct effect on the climatic conditions of a region. In our case study, the rate at which Erbil city is growing as had been mentioned earlier on have created a need of more buildings, roads and other infrastructures to be put up. This, on the other hand has seen to it the cultivation of more thus destroying the natural vegetation cover which in turn have caused the notable changes of the temperatures and the overall climate of Erbil city units (Busar & Hall, 2005).
Objectives of the research
Climatic changes are mostly felt in urban centers due to the fact that biophysical features are more distinctive in cities than in rural areas which are reflected in the UHI (Urban heat island) phenomenon (Fortuniak, 2009).Thus, the overall objective of this research was to find out the influence of urban growth of Erbil city on the air temperature trend. Other objectives apart from the major one are as follows
- To find out if there is an increase in the minimum air temperature (mainly
Minimum temperature) in Erbil City for the period 1975-2011.
- To compare the air temperature inside the city to the air temperature of the
Surrounding rural areas, on a regional level.
- To map the spatial pattern of temperature for Erbil City by using the thermal band
of ETM+ satellite for autumn 2011 to analyze the influence of different types Buildings and green areas on temperature patterns.
Once these objectives are full filled, the researcher will be in a position to prove the hypothesis that air temperature have of Erbil have increased due to urbanization to be either null or void.
The city of Erbil lies along latitudes 44°0′33″E) and longitudes of 36°11′28″N and is located in the north-east of Iraq it being the capital of Iraq Kurdistan region. This city is among the most 36°11′28″Noldest cities that have shown continuous inhibition with its inhibition being dated back at least back to 6000 BC. This city covers an area of approximately 130 square kilometers and it reflects a population of 1,025,000 people making it one of the largest cities in Iraq (KRG, 2012). The city is located in a low-lying area that is approximately 426 meters above sea level (Ayad, 2010).
According to Koppen climatic reports, Erbil city is located in a translational climatic zone that lies between Mediterranean climate and arid climate. This climate is characterized by warm to hot summer and cold to somehow cold winters. However warm nights are experienced but subzero temperatures are a thing of past in this city. Rainfall per annum is registered between 300-400mm which is concentrated during the month of April and August. As indicated by the graph below rainfall is lowest in June with 0mm with an average if maximum of 112mm when coming in January
On the other hand, as indicated by the graph below highest temperatures at Erbil city are experienced in the month of July while January is the coldest month displaying an average 7.40C
To enable the researcher to analyze the effect of urbanization on the local climate of the city in question and its surroundings, there was a need to make two databases as will be explained below
This data comprised of data recorded from all the weather stations which included maximum and minimum temperatures registered daily at all the weather stations then grouped into monthly and annual averages. All these stations reflected a time series of 1985 to 2011 as shown in the table below
Weather station time series latitude longitude latitude
Erbil(Urban) 1975-2011 36° 125 44° 025 420
Ainkawa 1985-2011 36° 14 44° 015 434
Kardarash 1985-2011 36° 07 44° 01 410
Kalak 1985-2011 36° 17 43° 44 252
Khoshtaab 1985-2011 35° 46 43° 35 275
Bastora 1985-2011 36°20 44° 10 270
Shaklawa 1985-2011 36° 25 43° 15 950
Salahalddin 1985-2011 36° 24 44° 014 1050
For evaluation of this data to be possible, a simple regression analysis was performed with the year forming the independent variable while temperature formed the dependent variable. It should, however, be noted that though some conclusions were made, the researcher only utilized the available data that is from 1975 to 2012. in order to determine the effect of Erbil urbanization with time and how this have affected temperature changes, time series data was divided into three shorter periods so as to cover up for any missing observation and extreme values.
The second type of data was derived from observation of satellite images which were used to produce land surface temperature (LST) and NDVI maps of the region. This image (Landsat ETM+) were taken on September 14th 2011 which indicated that the air temperatures of Erbil were approximately 340C and the humidity were 15%. Below is one sample of the satellite pictures showing the distribution of vegetation.
Satellite image preprocessing
As noted thereafter, this image was taken under favorite conditions which imply that there were no clouds to alter the form in which the outcome of the photo was. It was however preprocessed for rectification of radiometric or geometric distortion thus ensuring a level IG product. This rectification resulted to universal transverse Mercator (UTM) zone 29N coordinate system. According to the image obtained, land use the land cover (LULC) shape derived from the later image was used to determine the urban thermal environment. These LULC values were later involved in the calculation of the land surface temperature.
The results obtained from this research are related to the effect of urbanization on local climate of Erbil city. These results were divided in accordance with the source of data as discussed below.
To observe the impact of Erbil city growth on local climate, Edwin & Bruce 2010 suggested that the monthly minimum temperatures should be used because they are more affected by urban growth than the maximum temperatures
as indicated by this graph, the months of January February and December were used to plot graph of varying changes in temperatures as years rolled by because they presented the coldest months in Erbil city.
Having in mind that the graph is minimum temperature plotted against time, it is clearly noted that as time elapses, temperature tends to increase. This is true because years continue to roll on, the city continues to expand which means that more land is being used for construction of infrastructures thus ruining the natural vegetation cover which in turn have an effect on temperature
It is clear that when temperature change, an overall effect of vegetation cover is felt across the area in which the changes are reflected. In the case of Erbil city the same was experienced as indicated by the graph below
According to the distribution patterns and trend indicated here shows that the slope of the NVDI changed over time. The areas showing negative or positive trends show the areas that experienced vegetation degradation. From the data, the deduction that can be made and this are the planar distribution that is shown by the virtual distribution patterns of the vegetation cover over a given period. The data shows that the linear expansion of the urban center has contributed to the planar decline in vegetation over the time. There is a correlation between the vegetation distribution pattern and urbanization in the city (Edwin & Bruce, 2010). The significance level is evident in the climatic change and the overall NVDI change that has occurred over time. This is shown in the partial correlation between the NVDI and climatic changes over time and climate is the basic factor that drives changes in the vegetation cover. The changes in spatial vegetation distribution pattern in the Northern part of Iraq as shown in the time series is contributed to by the annual changes in temperatures.
The process of urbanization in the larger Erbil region shows the changes that can be caused by anthropogenic activities during the period of study. In the past 15 years in the larger Erbil, there has been a major change in terms of large-scale urbanization in the northern part of China. The change has been brought about by the need for houses and the large-scale inflow of population to cities like Erbil. The massive anthropogenic activities have contributed to the massive changes in vegetation in the study region. The variations in the vegetation cover in the urban regions is smoothing worth noting. There are factors that are worth noting in terms of the impact of urban expansion on the vegetation patterns as noted in the NVDI as shown in the figures (Garcia & Tejeda, 2009). The images show the impact of urban expansion on the vegetation density.
The NVDI changes between the years from 2000 to 2015 shows that the mean NVDI of the Erbil was 0.3585 in the outskirt areas of the city and 0.2365 in the core of the urban center. The difference in the mean between the urban and pre-urban areas show a huge difference of 0.122, and this means that there is a significant change in vegetation cover on the two regions. The difference shows high rates of anthropogenic activity in the Erbil city that in the outskirt regions of the city. The NVDI analysis shows that the vegetation density in the pie-urban areas increased significantly. The trend shows that human activities had a direct influence on the on the vegetation density in the study region. There are direct spatial changes in the population density between the urban and peri-urban areas.
In this section, a reflection of how urbanization have affected vegetation will be dealt with. To start with, degradation of nature is the major effect of urbanization since most of the natural vegetation covering will be cultivated to allow room for infrastructures. As if this is not enough, there are high chances of introduction of new species of plants being introduced which might not be favored climate conditions of the area they are introduced in.
The mean temperatures of earth have increased by about 0.80C since the twentieth century the reasons as to why this is happening have been attributed to changes in sun intensity, industrial revolution and transformation of porous bare and agriculture land to a non-porous material that permits nor the sun’s rays neither the runoff water to escape through it.
The urbanization process during the period of the study showed that the NVDI values changed significantly given the difference in the mean NVDI values between the city’s core and the outskirts if the city. The NVDI values over the years show significant spatial variation and the differences in value showed that human activities (Busar & Hall, 2005). The core areas in the Erbil city shows increased human activity that has contributed to the low vegetative cover in the area. There is a negative effect of human activity on the overall vegetation index across time series, and this supports the conclusion that human activities and development have an influence on the vegetation dynamics in the study area across the time series. The extent of vegetation change across the time series indicates how human activities across the study period. The process of urban expansion and the corresponding human activities had a direct impact on the vegetation patterns in Erbil region (Busar & Hall, 2005). The activities have led to the steadily declining vegetation cover in the expanding urban areas of Erbil. The replacements of natural vegetation cover with buildings and other human developments that have changed the overall outlook of the landscape over time. The changes can be attributed to the changing climatic patterns as a result of urbanization. The changes observed in the last 15 years shows that Erbil area has changed significantly, and the regression analysis shows the difference in the overall urbanization and vegetation cover change.
The anthropogenic activities in the open lands between the Erbil city core and the outskirts of the city are the reason for the rapidly changing environmental conditions, and this is coupled with the climatic conditions. Human activity has the ability to change the overall vegetative and climatic structure within cities, and this can explain the reason for the drastic rate of change of the nature of vegetation cover in the region after the relocation of people to the new regions outside the city (Erik, 2006). The MODIS data analysis from the satellite images shows that the nature of vegetative cover largely depends on the settlement patterns and also the temperature. As noted the plotted areas with lower overall temperature have higher vegetative cover when compared to the regions with high temperatures(NASA, 2010). The fully vegetated MODIS model shows that the region vegetation can distribute in terms of parks that showed the high vegetative cover, household gardens shown by the frontal gardens and sparse population and lastly the industrial regions with no vegetation. Generally, human encroachment has had a significant impact on the vegetation distribution patterns and dynamics in the Erbil region and with the expansion of urbanization, it is likely that the city will completely occupy the area covered by the parks and vegetation.
I would like to express my gratitude to all the individuals who made significant contributions to the accomplishment of this work. I am particularly grateful for the assistance from my colleagues who tirelessly provided me with the assistance I required particularly in data collection and interpretation and assisting me with the editorial work. I thank the NASA for allowing me to use the images from their satellite in justifying my research based on facts. Finally, I appreciate my collaborators whose significant contributions made this work a success.
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