Simulating informal settlements growth in Dar es Salaam, Tanzania a hierarchical framework

1
Simulating informal settlements growth in Dar es
Salaam, Tanzania a hierarchical framework

• Ellen-Wien Augustijn, Johannes Flacke and Asif
  Iqbal
• ICA Workshop 2009
• Gävle, Sweden

2
Factors leading to development and growth of
informal settlements

• weakness of the statutory planning process
• strong rural-urban migration leading
• Leading to
• Enormous population growth

• Other contributing factors
• problems with land tenure
• lack of formal surveyed building plots
• poor land administration systems

3
Prevailing urban trends in developing countries
Growth of informal settlement (ISG)

• approx. 80 of urban growth in developing
  countries is informal
• Informal settlements are densely populated urban
  residential areas with
• informal or insecure land tenure
• inadequate access to basic services
• no planning and no building permissions
• not necessarily slums
• global phenomenon (for LDC), varying pattern

4
(No Transcript)
5

• Informal settlement process differs from a formal
  settlement process
• A limited number of simulation models were
  developed for informal settlements
• No body of theory exists for the development of
  IS in developing countries, simulation models can
  contribute to a better understanding of the
  process and theory development.

6
ISG in Dar es Salaam, Tanzania

• 70 of growth in informal
• majority of the settlers buy/inherit the land
• accommodates a wide variety of social groups of
  different income level
• Densities are low in the beginning and increase
  over time
• Development of vacant or agricultural land

7
ISG in Dar es Salaam, Tanzania
1967
1975

• Initial settlement on peripheral land
• Simple low cost houses
• Consolidation with own improvements
• Beginning of room rental market
• Government involvement (upgrading)
• Increase in absentee owners
• Continual improvements, gentrification

1987
1982
8
Relating IS to hierarchy theory
Hierarchy theory
Informal Settlements

• Land use change is generally seen as a
  multi-scale process in which processes - driving
  factors operate at different scales
• Besides the individual settler, other actors are
  actively responsible for the growth and change in
  informal settlements. These actors include the
  local government. (vertical structure)
• Horizontally three subsystems can be identified

• complex systems have two lines of organization, a
  vertical structure and a horizontal structure.
• The vertical structure is composed of levels and
  the horizontal structure of sub models (Wu and
  David, 2002).
• Each hierarchical level has a particular rate of
  processes where higher levels have a slower
  process and lower levels have a faster

9
Factors influencing ISG - sub models
Economic factors
Physical factors
Land quality
Gentrification
Commercial Room rental
Accessibility
ISG
Upgraded utilities
Land prices
traditional systems
Social contacts
Family ties
Cultural factors
10
Objective

• The objective of this study is to create a two
  level hierarchical model consisting of
• a city wide settlement model
• a micro-level housing model

11
Conceptual framework
City level or settlement model
Housing Model
12
Driving factors
13
Conceptual framework

• Settlement model
• Raster based
• Temporal resolution year
• Actors include government
• Growth of settlements, new roads, upgrading from
  informal to formal

• Housing model
• Vector based
• Temporal resolution day to month
• Actor is the family
• Choice of plot, building of houses, renting of
  rooms

14
Implementation of the housing model

• Movement of Agents
• New Agents are created at a random location
• Agent will move to the closest house
• Movement from centroid to centroid
• agent will select a new house within its search
  radius
• Settlement Behavior
• Cross-Layer Feedbacks

15
Implementation of the housing model

• Movement of Agents
• Settlement Behavior
• new houses are built next to existing houses
• The space required varies per type of building
• When sufficient space is available the agent will
  check cost factors and attractiveness of the
  location calculating the suitability
• Cross-Layer Feedbacks

16
Implementation of the housing model

• Movement of Agents
• Settlement Behavior
• New house
• Extension of an existing house
• Only small or medium size houses can be extended
• small houses will always be situated between the
  existing house and the road
• Cross-Layer Feedbacks

17
Results

• Test runs were conducted for the time period 1987
  to 1992 for Manzese settlement
• Agents have preferences related to distance to
  roads and footpaths (roads being preferred above
  footpaths), and an avoidance behavior in relation
  to the flood risk areas.
• Agents belong to different income groups and are
  either tenants or house owners.
• Existing buildings (as polygons), infrastructure
  and the flood zone are used as input.

18
Results
Existing houses
Simulated house
Flood zone
Foot path
Road
19
Discussion

• Aim of the project described here is to develop a
  two-layer hierarchical model containing an
  economic model, a social model and a landscape
  model. Only one layer of this model (the micro
  housing level) has been implemented so far
• Improvements on the housing model
• Development of the city level model

20
Limitations of the existing housing model

• The current model is only suitable for modeling
  the densification process not for new spontaneous
  growth.
• Of the social aspects only the difference between
  owners and tenants is implemented. This aspect
  can be further extended.
• Currently the model only contains the roads,
  footpaths and flood zone area as physical
  features. This should be extended to include the
  slope, water distribution points, and possibly
  the access to utility infrastructure.
• There is no mechanism of selling houses, so
  agents that settle in the area will not leave
  this is an unrealistic limitation of the model.

21
Validation of the housing model

• the predictive accuracy (correlation with actual
  data)
• Extensive data are available
• Tests can be conducted on other informal
  settlements and different time periods
• process accuracy
• Difficult although some processes are documented