More than 50% of the world’s population is expected to live in urban areas by 2020 [1
]. In addition, the world population is expected to rise from 3.6 billion in 2011 to 6.3 billion in 2050. Presently, there are 23 megacities globally hosting 9.9% of the world’s urban population, and they will increase to 37 by 2050, hosting 13.6% of the world’s urban population [1
]. As urban surfaces cover 3%–5% of Earth’s total land surface [3
], the environmental impacts of urbanization have become a major concern around the world [2
]. Urbanization is a widespread anthropogenic cause of loss of arable land [4
], habitat destruction [5
], and decline in natural vegetation cover. It has severe effects on local ecosystems [6
], causes the urban heat island phenomenon [7
], consumes valuable productive arable land [4
], results in loss of habitat and biodiversity [8
], and also causes global effects such as climate change [9
Urbanization is often characterized by severe changes that directly affect the human environment and are accompanied by highly negative influences on the global carbon cycle, such as an increase in atmospheric CO2
]. Moreover, the absence of proper urban plans in developing countries to deal with this dilemma has caused several additional problems such as inadequate housing supply, haphazard development, urban poverty, and inequity of land supply, which lead to the rapid emergence of slums and unplanned urban areas [13
In Egypt, rapid urbanization had been witnessed over the past three decades, notwithstanding governmental attempts to reduce it. The urban population in Egypt had increased from less than 10% at the onset of the 20th century to more than 45% by the end of the 20th century. The annual growth rate of the urban population is estimated to be 2.2% until 2050—surpassing the existing 1.8% annual growth rate of the rural and urban population [14
]. The current population of the greater Cairo metropolitan region (GCMR) is estimated at 17 million inhabitants, which corresponds to nearly a quarter of Egypt’s population of 72,798 million inhabitants in 2006, and about half of the country’s population lives in cities. Currently, the population of the GCMR (Figure 1
) is estimated to grow at nearly 2.0% per annum. However, the labor force will grow by over 3.0% annually, because 33% of the total population in the GCMR is under 15 years old and expected to reach working age during the current decade. The sex ratio for Cairo is precisely the same as that of the entire country (48.8% of inhabitants are female).
The population of today’s GCMR has grown since 1950 to be 2.4 million in 1975, 6.4 million in 1986, 12.5 million in 1996, and 17 million in 2006 [16
]. The metropolis’s informal urbanization (IU) is supported by a natural increase and the amalgamation of rural populations. In the GCMR, more than seven million inhabitants dwell in informal areas; 80% are living on privately owned arable land [14
]. The informal urbanized areas have expanded particularly on private arable land and, less customarily, on publicly owned desert land. By 2025, around 50% of Egypt’s urban population is anticipated to dwell in informal areas [14
]. During the mid-1980s, the region’s population grew at a rate of 2.6% annually [18
]. A study using satellite images detected that the surface area covered by IU in the GCMR between 1991 and 1998 grew by 3.4% per annum, while the population living in the informal areas grew by 3.2% per annum (200,000 people per annum). On the other hand, between 1986 and 1996, the population growth rate of IU areas was 3.4% per year compared to the official estimate of 0.3% annually [19
]. Moreover, it has been estimated that more than 1.5 million acres of arable lands have been wasted in Egypt because of the IU activities over the last 30 years [19
In order to mitigate the detrimental effects of informal urbanization on the environment and to maintain the ecosystem functioning [21
], it is essential to identify the factors influencing IU in order to support urban planners, resource managers, economists, and environmentalists in solving the problems associated with this phenomenon [2
]. Therefore, this paper seeks to investigate the driving forces (DFs) of IU in the western part of the GCMR from 2004 to 2013 using the Analytic Hierarchy Process (AHP). It is crucial to study and understand the nature of the IU phenomenon to stop its negative consequences on land resources and on quality of life in the GCMR, which shelters half of Egypt’s urban population. The GCMR greatly needs precautions against IU to maintain its role as a capital, major political center, tourist attraction point, and major economic hub [16
Modeling DFs, which comprise urban planners’ observations, and deriving a structural concept of IU procedures have been difficult for many years [26
], as various forces execute various functions at various scales in a specific place. DFs are usually integrated, and it is reasonable that one force can influence diverse forces in the IU process [27
], while these forces are working as indicators to grasp and quantify the nature of relationships between the IU phenomenon and its causes, which physically alter land use over urban areas. Although various methods, from probabilistic to econometric, are used to grasp the driving forces in different major highly urbanized regions such as Kathmandu, Nepal [26
], the AHP method [28
] was applied in this research to grasp the process of IU as it can be used to model municipal planners’ observations identified through a questionnaire, and it identifies accurate indices to describe the correlations amongst forces.
Urban sprawl is considered the physical outcome of the IU phenomenon, and is often the commonly used term. The IU phenomenon represents the expansion of urban areas occurring outside of the authorized urban plans [31
]. This outgrowth, seen along the periphery of cities, along highways, and along roads connecting a city, lacks basic amenities like sewage, potable water supply, and major health services [2
A comprehensive literature review carried out for this paper found that previous researchers have categorized DFs into two main classes, physical and socioeconomic. Physical DFs are determined by biophysical characteristics of the environment such as topography, spatial configuration, climate, soil type, and natural disturbances [33
]. Socioeconomic DFs can be determined by the human utilization of land resources to meet life needs [33
], which could be divided into four categories: political, economic, cultural, and technological DFs [34
]. Typically these DF categories are not clearly separable; for example, political and economic DFs are closely interrelated with political steering of economic mechanisms. However, previous studies have identified the main DFs of IU in developing countries based on several case studies [22
]. Several DFs such as land market and landholder speculation, local government’s willingness to lease land as a result of new tax revenue regulations, decentralization process after economic reforms in developing countries, population growth, increase in demand for housing space, construction demand for new development zones, demographic changes, foreign direct investment, transition of land-use regulations, rise in urban residents’ income, the gradual monetization of housing distribution, rapid economic development, and shortcomings of land management system [35
] can be observed in multiple studies.
On the other hand, AHP is widely used in the area of urban planning studies; for example, AHP is widely applied in landscape planning and assessment research [39
], and site suitability analysis research [41
]. In recent studies, AHP was applied to identify land-use suitability and to deal with the problems of preference acquisition [45
], synthesis, and inconsistent diagnosis that were not completely solved by the Saaty’s AHP method. AHP has also been used in the following studies: a demonstration of the use of a PLUS method for a greenway suitability analysis in central Arizona was performed by AHP [46
], applying AHP in developing a multi-criteria decision-making method to define parameter values for CA simulation empirically [47
], applying AHP methodology as a combined cost-benefits analysis and environmental assessment for a petroleum pipeline project [48
], and creating a development-suitability map for the geo-environment around megacities [49
]. Therefore, we applied the AHP method in this research to identify the weights of DFs in the GCMR.
The alterations in the spatial patterns due to IU in the study area during the last three decades were supported by improvements in transportation networks and the accomplishment of several governmental development plans [66
]. With the growth in residents’ knowledge and public culture, diverse DF has led to alterations to the terrain in the previous decades. Many of these forces, in various proportions, have been identified as significant in other studies. For instance, economic incentives and population growth were identified as significant DFs by [68
]. Moreover, public community issues, diversity of transportation modes, neighborhood relations, municipal plans, and political, economic, cultural, technological, and structural affairs were identified to be DFs with various influences in similar studies [27
]. Comparing our findings with similar developing countries case studies such as in the Dhaka region in Bangladesh, we noticed that the main driving forces for urbanization procedures in Dhaka were land speculation, land prices, growing demand for housing, topography, land use, transportation, economic activities, and population growth [10
]. These drivers are similar to our findings in the GCMR, with small differences in the order of drivers’ importance.
5.1. Comparing the Driving Forces by Structural Areas
When comparing the DF outcomes by study sector in Figure 7
, it is clear that the influence of the geographical characteristics force is higher in the south sector than other sectors. Considerable numbers of brick manufacturers are located in the south sector because of the suitable soil properties [25
]. The geographical characteristics force is not that significant in the middle sector because of the high rate of yield. Businesspeople and investors are progressively interested in exploiting the land despite physiographic restrictions. Furthermore, other effective forces often disguise this force. For instance, due to the higher availability of facilities and the functional intricacy, the availability of facilities force had the highest influence on the south sector compared to other sectors, where most of the services are limited. Moreover, the setting up of new commercial projects was observed in neighborhoods closer to the facilities, which is a new tendency.
The impact of economic incentives in the south sector is less than half that in the middle sector. The land demand and supply force has the highest influence in the south sector, closely followed by the north sector. Land in the south sector is obtained at a lesser cost for new developments or land trades, while land speculators and local people are very active in land trade in the north sector. These characteristics may describe why the land demand and supply force is relatively higher in these areas than in the middle sector.
The population increase force is more influential in altering the north sector terrain than in the middle and south sectors. Some of the native residents are active in maintaining their ancestral land. Consequently, population increase persists. Moreover, investors are attracted to the north sector areas in the GCMR for developing residential buildings. Some of the new top-class residential areas are in these north sector areas. As the population increases, demand for housing escalates. The population increase force was rated lower in the middle and south sectors.
The administrative function force in the south sector has a higher function in altering the rural terrain than in the middle and north sectors. The development plans force has the least influence in the south sector, due to the poor accomplishment of government development plans in the last three decades, as has been asserted by other studies [15
5.2. Rating of Driving Forces by Study Sector
shows the DFs ranked from 1st order to 7th order. Administrative function force is the highest-ranked DF in the south sector, but it was only 5th and 4th in the north and middle sectors, respectively. This has been a significant theme for a few decades in Egypt. Through the previous three decades, considerable numbers of people in Egypt moved to the Cairo region, as it was found to be the most affordable place to work and live in Egypt. Some of the newcomers became the source of labor for the manufacturing and real estate sectors. The influence of population increase force is the 2nd most crucial DF in both the middle and south sectors with a rating of 6, and is rated 7th in the north sector. This indicates that population increase has a higher influence on terrain alteration in the north sector. The land demand and supply force looks to have the lowest rating, at 6th, 5th, and 3rd in the north, south, and middle sectors, respectively.
The geographical characteristics force had the smallest influence in the middle and north sectors, but it was rated 4th in the south sector. The economic incentives force had the top rate in the middle sector, but it was 4th and 3rd in the north and south sectors, respectively. This is because there are more business and employment opportunities in the middle sector as diverse classical residential areas in the middle sector are being converted to businesses. In contrast, this force has a lesser function in rural areas because there are fewer opportunities for investment and work.
The function of development plans is not as considerable in the study area. It is the 2nd least influential force in all of the three sectors in the study area. Residents state that government development plans have been implemented imperfectly, with no effect in altering the terrain. Because of the lack of availability of facilities in the south sector, it ranked the lowest in this sector, and with growing accessibility to the middle sector, its influence decreased, from the 3rd order in the north sector to the 5th in the middle sector.
Ultimately, economic incentives, population increase, and administrative function forces are the highest-rated forces influencing IU in the middle, north, and south sectors, respectively. As shown in Figure 7
, two forces, population increase and land demand and supply, extended the 6th order. The geographical characteristics force seems to be the least influential force in the middle and north sectors, while the availability of facilities force is the least influential in the south sector.