Endüstri etkisinde bir kentsel sistemin dinamik büyüme modeli

Abstract

ÖZET Çağdaş teknolojideki ilerlemeler, günümüz kentlerinin sosyal ve ekonomik yapısında da hızlı değişimlere neden olmaktadır. Kent sisteminin elemanları arasındaki etkileşim giderek yo ğunlaşırken, kentsel yapı da giderek daha karmaşık bir hale gelir. Kentsel yapının öğelerinin birbirinden ayrılmaz bir bütün ol duğu gerçeği, çalışmamızda temel yaklaşım olarak `sistem yak laşımını` kullanmamızı gerektirmiştir. Sistem yaklaşımı ile kentlerin yapısını incelerken, kent; nüfus, endüstri, hizmet olmak üzere 3 alt sistemin oluşturduğu bir bütün olarak ele ahnıı ştır. Kentsel sistemin diğer bir özelliği ise öğeleri arasında kar şılıklı etkileşim olmasıdır. Bu etkileşim zaman boyutu için de, kentsel süreçleri, ya da kent dinamiklerini ortaya çıkar maktadır. Kentsel sistemin dinamiklerini ve kent sistemini oluşturan süreçleri anlayabilmek amacıyla son yıllarda geliş tirilen yaklaşımlardan biri de `Kent Dinamikleri` yaklaşımı dır. Çok sayıda değişken içeren, karmaşık bir sistem olan kent sis temini oluşturan süreçleri kavrayabilmenin en iyi yolu, ger çeğin basitleştirmesi olarak ifade edebileceğimiz `kentsel model leme`d ir.Kent Dinamikleri yaklaşımını kullanarak, bir kentsel model örneği geliştirilen bu çalışmanın amacı, kent sistemini, 'nüfus, sanayi, hizmet gibi kent değişkenleri arasındaki neden- sonuç ilişkileri açısından modellemek ve model üzerinde dene meler yaparak, kent sisteminin temel bileşenlerinin oluşturduğu etkileşimleri yorumlamaktır. Bu amaçla, sistem düşüncesinin bir ürünü olan `Sistem Dinamiği` yaklaşımından yararlanılarak bir model geliştirilmiştir. Çalışma esas olarak dört bölümden oluşmaktadır: Birinci bölümde, modelimizin temel felsefesini oluşturan sis tem düşüncesi açıklanmıştır. Bunun için öncelikle, sistem kavramı tanımlanmış, bu kavramdan kaynaklanan sistem yaklaşımının temel nitelikleri belirlenmiştir. Daha sonra, sistem dinamiğinin bir disiplin olarak belirginleşmesini sağlayan koşullar vurgulanarak, bu yaklaşımın özellikleri, tanımı, felsefesi ve amacı belirlenmiştir. Bölümün sonunda ise sistem dinamiği yönteminin ana aşamaları tanımlanmıştır. İkinci bölüm, sistem düşüncesi açısından, kent sisteminin tanımlanmasına ayrılmıştır. Bu amaçla, öncelikle kent sisteminin çevresi açıklanmış ve kenti oluşturan alt sistemlere iliş kin değişik görüşler verilmiştir. Daha sonra kentin modellenmesi kavramı üzerinde durularak, kent modellemesi alanında yapılan değişik araştırmalar ve eleştirilerden örnekler sergilenmiştir. Üçüncü bölümde, geliştirdiğimiz `Kentsel Davranış Modeli` yer almaktadır. Burada, önce, sistem dinamiği anlayışı açısından kent sistemi tanımlanmış ve sistemin alt sistemleri belirlenmiştir. Daha sonra, kent sisteminin içindeki neden-sonuç ilişkilerini sergileyen `Etki Diyagramları` kurularak, bu ilişkilerin özel ve standart sembollerle gösterilmesini sağ-Layan ve böylelikle matematik denklemlerin kurulmasını kolaylaştıran '' Akış Diyogramları'' oluşturulmuştur. Bu bölüm, kent sistemi içindeki ilişkilerin ve süreçlerin matematik açıklamasını vere DYNAM denklemlerinin hazırlanmasıyla son bulmuştur. Dördüncü bölümde, modelin uygulaması verilmiştir. Burada, modelin uygulama alanı olarak seçilen İzmir-Aliağa yerleşmesinin coğrafi, ekonomik ve sosyal özellikleri tanıtılmıştır.1965'lerden başlayarak perto- kimya sanayi ve buna bağlı diğer yan sanayilerin gelmesiyle, bölgedeki işlevi ve fizik- mekansal dokusu hızla farklılaşan, yakın zamanda serbest bölge alanı seçilmesi nedeniyle daha da büyük gelişmelere sahne alacağı beklenen Aliağa yerleşmesinin, üçüncü bölümde geliştirilen modelin kurgusuna uygun bir örnek çalışma yeri olduğu belirtilmiştir.Modelden elde edilen sonuçlar üç ayrı alt bölüm halinde sergilenmiştir.Önce, ilk 25 yıl içim modelin sonuçları daha sonra uzun zaman boyutu içinde elde edilen sonuçları; son olarak da Endüstri Büyüme Faktörü arttırıldığı zaman elde edilen sonuçlar sunulmuştur.Bu bölüm, genel sonuç ve değerlendirmelerle son bulmuştur.

DYNAMIC GROWTH MODEL OF AN URBAN SYSTEM UNDER THE INFLUENCE OF INDUSTRIAL GROWTH SUMMARY This study present: the practice of systems approach as it has been developed during the last two decades in social policy in general, and urban planning in particular. It is argued that one of. the derivations of the systems approach, namely system dynamics provides a useful methodological tool for the analysis of contemporary urban problems, and processes. In a reiated context, the argument also suggests that, methods which emphasize structure and pattern in social systems in general and urban systems in particular, rather than elemental detail, are worthy of much greater development. The city is a complex system capable of counter intuitive responses which cai be properly understood and controlled only if the interaction between the basic urban sub-systems are taken into consideration properly. In other words, the main question is not to better understand the individual sub systems (population, service, industry), but to' understand how they act together, how they are harmonized into this entity we call a city. The solution of many critical urban problems depends precisely upon our capability to recognize the complexity of the urban systems in an explicit manner so that the solutions are brought in reference to all relevant inf luences. This study consists of 5 sections. In the first section, the systems approach which forms the basis of our model is explained. Then, the definition of the system is given and its main characteristics are explained. The system is defined as an interacting, 'and goal directed set of objects taking place in an environment.- vıı - o When considering any part icul ar problem, one uses the broadest possible context. Whatever the system one focuses attention on, it is recognized that a study can not be limited to include the concepts from a single traditional discipline, e.g. economics, sociology, architecture etc. On the contrary, there is a need of interdisciplinary study, and dependence on the methodological tools from a large- number of areas. o In describing the various factors of importance for the given urban problem, primary emphasis has. been placed upon both the relationships between the factors as well as upon identifying the inner mechanisms which produce the observed behaviour. The future, then, is assessed not on the basis of extrapolating past trends, but rather on the basis of understanding the effects determined by these inner mechanisms and how they affect the future. This is in essence where the urban dynamics studies differ from the more traditional urban planning. In the second section, the definition of the urban system is given. For this purpose, firstly the environment of the city is explained and the concept of urban modelling is introduced A model is a representation of reality. It usually includes a simplified and generalized statement of the most important characteristics of the real-world situation. Model is an abstraction from reality. Urban models were first built in North America over twenty years ago as part of the growing real izat ion that the power of digital computer might provide a means for handling complex systems manifesting complex problems. Thus urban models were policy-orientated from the beginning. These models remain as vehicles for developing policy, rather than building a framework for testing the scientific theory. Models are classified on various basis by different authors. One of the basic distinction is betweenstatic and dynamic models. The importance of time dimension is taken into consideration in dynamic models. As the city is a dynamic and ever-changing system, one of the dynamic models, namely the system dynamics model is used in this study. In this context, it is possible to identify two complementary objectives of the use of models in urban planning. The first is a desire to uncover the dynamics of urban development as a means of advancing the theory of urban growth, and making theory operational so that it can be refined and tested. The second is a desire to use models as a means of projecting the future state of the systems. In the third- section, an Urban Dynamics Model, namely `Urban Behaviour Model` is presented. In this section, first the concept of urban system is described using the system dynamics approach, and the sub-systems of the urban system are presented. System dynamics focuses on the structure and behaviour of systems composed of interacting feedback loops. DYNAMO flow diagrams and causal loop diagrams offer a convenient way to represent loop structures before development of system equations. Causal loop diagrams play two important roles in system dynamics studies. First, during model development, they serve as preliminary sketches of causal hypotheses. Second, causal-loop diagrams allow the analyst to quickly communicate the structural assumptions underlying his model. The main structure of the model is explained below: The present model, examines the life cycle of an urban area using the methods of system dynamics. The urban area is defined as a system of interacting industries, services (housing and other urban equipments) and people, i.e. the population. The growth model starts with a scarcely populated land area and generates the life cycle of development leading to almost full land occupancy and equilibrium. Aside from attractivelocation, climate and recreational facilities. Job' availability is the primary` determinant of population growth in the community. The `community's attractive qualities bring people in the area. Under these conditions, residents are also leaving the area- for various reasons. Besides migration flows into an d out of the area, the population is increasing naturally by births and decreasing by deaths. The construc tion industry responds both to availability of industry and services, and land avai lab i 1 i t-y within the area. New.construc tion continues as long a~s plenty of free land remains available for future choices. As the area develops and its land area fills, the process of aging.cause stagnation. As the urban area moves from the growth phase, the population mix and the -economic 'activity change. The dynamic systems are seen as feedback processes having a specific and orderly structure. The dynamic behaviour arises from the structure of the particular system. A digital computer is' then used to simulate the behaviour of the system. The computer sy.stem reveals the dynamic characteris tic of the system that was. described in the structure - formulating stage. By changing the guiding policies within the system, one.can see how the behaviour of the actual system might be modified.. In the fourth section, a small town in the Western coast of Anatolia, namely Aliağa is presented. Aliağa is chosen as a case study to relate the model to real-world situation. Aliağa is found to be an appropriate settlement for the application of the model as it is in consistence with the structure of the model. Petrochemical industry and the other related industries and the external economics it brought, starting from 1965's; transformed the village to an expanding and rapidly growing city..In the fifth section, the results of the study are presented. This study, aims prim.arily to introduce a model of urban behaviour and to illustrate how structural assumptions deter mine model behaviour. The first run contains the standart run of the model. The first 25 years are marked by rapid growth and development. In-migration and construction grow exponentially while out-migration is practically negligible. The positive loops involving population, industry and service. construction, and migration dominate this phase. The second run contains the long range run of the model. In the longer time dimension, construction reaches its maximum and begins to decline as the choice land fills up and the construction industry must restrict construction. Industrial building construction continues to grow but at a decreasing rate.. The service ratio begins to decline, thereby retarding migration and accelerating ou t-migrat ion. Because of land constraint, and in spite of excess demand, the construction rate continues to decline until construction Just equals demolition. The negative loop involving land dominates. Industrial growth factor is increased in the third run of the model, and the behavioral change of the model is analyzed. The general conclusions of the study are presented in the fifth section. When using the models and interpreting the results it is 5 important to be fully aware of the assumptions, limita tions, and problems that are involved. Too much cannot be expected from these uiban models. In fact, a perfect reproduc tion of the real world situation is just not possible. However, by using existing data which can be supplemented by »further survey work, a great deal of useful information can be produced from a modelling exercise. When analyzing the urban system or looking at the consequences of planning policy decisions or development decisions, then urban modelling can be a useful part of that analysis.The urban dynamics model, and extensions of them, should be a basis of future, influence on political decisions. First, when modified to reflect a city's specific features, the model can be employed as a policy guide for urban planning. Second extensions of the models can focus on specific urban issues such as education, transportation, and social integra tion. Third, the models can provide a basis for a clearer understanding of urban processes and a better informed percep tion of how different aspects of a city affect one another. Urban dynamics provides a framework for interrelating different sub-systems of the city and allowing for the investigation of the logical consequences o I alternative policy actions. Regarding urban planning as a policy process, reveals an over-riding feature. It is that planners will manipulate and operate the system so as to influence its performance in the way they want it to work. In my view, the social dimension of urban and regional planning is the most important dimension. Systems dynamics approach can be used as an analytical tool in the future, to study societal dynamics, and to derive alternative development policies.