Analyzing of Reduction Process of Urban Open Spaces in Process of Cities Development with Emphasis on Crisis Management in Tehran Metropolis

,


Introduce the Problem
Urban open spaces are one of the importance Infrastructure that could be used them in process of crisis management as effective and efficient spaces in order to reduce the damage of disaster (earthquake, volcano, flood, etc.).We can use these spaces, while happening crisis as relief base; also we use them as temporary accommodations.
Iran has been located in dangerous place due to geological conditions and geographic location.Thus, are accruing damages due to natural disaster such as flood and earthquake.
These are factors that increase harmful effects of disasters such as: construction in high-risk areas, disregard to strength and proper distribution of buildings and vital installations, existence of heterogeneous and urban old structures and etc.Also Lack of awareness and readiness of the people and authorities are double factor in aggravating deaths and injuries disasters.
While accruing crisis, will appear physical damage in various form in urban environment due to instability of elements and urban areas in crisis (earthquake, flood) in short time.
In these situation, not only rescue group and army is not enough to save residents but also should be used various sciences and knowledge such as Architecture & Urbanism and crisis management in order to reduce human damages, critical and sensitive equipment, infrastructure services and critical needs.Today in many of cities in country especially in Tehran are reduced open spaces due to uncontrolled construction of building in cities.The reduction of green, open, sport spaces could be studied during in 40 years ago in Tehran.Although in this period there are urban development plans but these natural potencies and advocacy tools damage more than other times.On the other hand, there are low per capita of green space and sport lands, also imbalance in distribution of function in urban development plans have been led to that is accursed a great shortage such spaces (open space, green space) in many of compact and central area of city.
Conversation process of green space, open space and sport space to commercial and office spaces are more faster than conversation other spaces to green & sport spaces.

Method
This study has been done in five steps that they are: 1) Studying of reduction process of urban open spaces in Tehran development process, 2) Structuring dynamic variable, 3) Formulation of simulations models, 4) Experiment, 5) Design and review of policies.

Studying of Reduction Process of Urban Open Spaces in Tehran Development Process
Have been mentioned basics variables for creating models and identifying effective mechanisms in reducing Tehran open spaces in the last 40 such as: 1) The areas of urban open spaces 2) The areas of urban spaces that has been built 3) Population (Table 1)  3).Social, economic and physical factors that have been considered in conceptual model problem show that the highest changes have been in recent 40 years ago.So, in this research in order to creating corrective mechanisms in studied system has been considered twenty -year period as standard ratio due to lack of access to statistic this period, on the other hand reduction process of urban open spaces are different.

Reference Variable Behavior
The main variable is usable open space in crisis conditions or spaces that have passive defense potential.This variable is assessed as state variable because the amounts of these areas are measurable in different times.State variable in studied period have faced reduction process.According to Tehran satellite images, the amount of urban open spaces decrease by using in temporary condition approach.

Structuring Dynamic Variable
In this section after identifying effective variables in problems and effective mechanism in behavior reference variable create dynamic variables.Thus at first is determined system boundary.After that has been defied cause -effect conceptual graph (Table 3).Also in second ring, increasing of population is led to need for housing production again.By increasing of construction are reduced urban open spaces.On the other hand in this ring by increasing open areas is activated population growth and demand for construction again.The distribution of main land use is one of the most important issues in order to planning of future in cities.So should be balanced between allocated space with Communication of network system and open space system in future.The distribution of land uses depend on especial condition in city and quality of planning.

Formulation of Simulations Models
Generally, the areas of residential spaces and element services in medium urban density are in Table 4.  re 10) (Table 7 20 years period  About the stat variable (built spaces) will increase for population growth during time.
Output rate has been considered for built areas due to is controlled by identified factors.
According to graphs and output value after running the model is determined.At the begging of 20 years period is started from 4.2e+008 to 4.3537e+008at finally of period.
Comparison of this graph with open areas graph show that has been controlled declined of urban open spaces process.Indeed remain stable following relation: Open Space / Built Space ≈0.66

Results
One of the most important issues that should be considered in crisis management is appropriate distributions infrastructure such as: emergency routes, safe open spaces, search and rescue and relief centers and emergency medical centers.
In this research was determined that some policies and macro -economic issues such as, focus resources and facilities in Tehran metropolis have been led to loss of balance between urban open spaces and built spaces in 40 years periods.There are some local policies such as sailing of density by municipal especially in two decade ago that has been led to physical development of city.Thus will be decreased urban open spaces.
Therefore in this study has been created the controlled mechanisms of balance between full and empty spaces.Also we expect that be prevented from reduction process of open spaces and reduction of urban space quality in 20 years periods with definition standard rate of these spaces (according standard of Tehran metropolis, Open Space / Built Space ≈0.66).
According to studies from 2004 to 2005, over 600 cases of open and green spaces have changed to residential and commercial land use legally (Behzaffar, 2009).According to status quo studies of Tehran comprehensive plan, totally the area of green space is 4463 acre in 1986.This land use has been distributed imbalance in city.The area of land use is 1486 acre in 5 districts of Tehran while the area of land use in 7 & 10 districts were only 2 & 3 acre.In these periods 1&7 districts had 40.6 & 0.07 per capita (Atak, 1992).So it is necessary that is predicted these open spaces to preventing reduce these spaces, also creating balance in order to improving quality of urban environment and preparation for possible crisis (Figures1 & 2).

Figure 1 .
Figure 1.There are some green spaces in density & organic tissue of Tehran

Figure 3 .
Figure 3. Sample of vacant lands that have been built in north east of Tehran

Figure 4 .
Figure 4.In last years have been built some lands that usable in temporary condition Figure 5.
2.3.1 Determines Structure and Modeling RulesThe structures of model consist of effective variables such as population, built areas and urban open spaces areas.Furthermore have been considered auxiliary variables such as (income people -loans granted) in order to definition of logical relations of system.2.3.2Estimated Parameters, Relations and Initial ConditionsAccording to existing condition and corrective polices for controlling destructive mechanisms and preventing reduction of urban open spaces was designed model that consist of: 1) Urban population, 2) The number of built spaces in city, 3) the number of open spaces in city (Figure7).

Figure
Figure 7. Flow graph

Figure
Figure 8. Pr

The areas of urban open spaces: This
variable is as reference variable.Other variables are considered with formation increasing and decreasing mechanisms in changing of amount urban open spaces during the time.So has been considered as state variable (Figure

Table 3 .
Determining of System Boundary

Table 4 .
The composition of main land uses In this model has been tried that is created balance between the areas of built spaces and the areas of urban open spaces.It means:

Table 7 .
Pr Policies in Order to Correction Destructive Mechanisms and Controlling of Reduction of Reference VariableSome policies is proposed in order to correction destructive mechanisms and controlling of reduction of reference variable (the amount of urban open spaces) after reviewing the existing conditions and identifying effective mechanisms in creating crisis conditions according to cause-effect graph.a)According to increasing of population and creating demand for producing residential buildings is decreased the construction process also is reduced urban useful spaces.Therefore, are proposed polities in order to controlling of construction demand from source management and urban population in cause-effect rings.These polities can be included appropriate economic and social leverage that strengthen migration from city.b)According to additive cause-effect ring, by increasing automobile is increased the need for travel spaces.So, are decreased poetical open spaces.Thus it is necessary that are adapted the amount of automobile with urban population and open spaces until is to widening the streets.c)Inaddictive ring that it is observable on cause-effect graph, decreasing of municipal budget is caused to sailing of density.The sailing of density create the next mechanisms in order to decreasing urban open spaces.There for, sailing of density should be replaced by other mechanisms.For example municipal can provide their budget from public funds.The following results are obtained after running of model according to graphs and output value of main variables:About the main variable (urban open spaces), the variable graph decrease with moderate gradient, by using of controlling construction policies in 20 years periods.At the begging of 20 years period is started from 2.8e+008 to 2.65741e+008 at finally of period.It show that is controlled, sharp declined of urban open spaces.The proportions between full and empty spaces are 0.4 in 20 year period.