Modelling informal urban growth under rapid urbanisation
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Date
2010-06-30
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Abstract
Dar es Salaam in Tanzania is one of the fastest growing urban agglomerations in Africa
and projected to become a megacity (i.e., a city with more than 5 mio. inhabitants) by
2025. Rapid urban growth under poverty has outstripped the capacities of planning
authorities to cope with the enormous pace of urban expansion. As a consequence
informal settlements absorb almost all urban settlers leading to rapid urban sprawl into
the unplanned periphery. But still only little is known about the drivers and mechanisms
of ongoing urbanisation processes and the means of intervention. The need for well
balanced and informed decisions becomes evident and calls inter alia for support of
urban planning by geo-information technology and so-called decision support systems.
This thesis approaches these needs by designing a land-use simulation model for the
city of Dar es Salaam.
Particularly in developing countries urban modelling inevitably comprises the challenge
of setting up an appropriate database. Public authorities in Dar es Salaam lack precise
and up-to-date information and were unable to contribute to the database needed for
the modelling work particularly since multi-temporal information was required. Basic
datasets which have been provided by another research institution were extended and
updated to serve as the database required by the analysis and modelling work.
The model presented is based on standard GIS software and designed along the
principles of Cellular Automata (CA) which are particularly suitable to capture
neighbourhood dynamics and likewise do not demand for a highly sophisticated
database. Population projections by the UN Population Division have been used to
determine future demand for informal residential land. The model simulates its
allocation based on variables which represent major drivers of informal urban growth:
natural conditions, accessibility and local-scale dynamics, i.e., so-called neighbourhood
effects. These drivers have been proven to be adequate to explain and project urban
growth during the process of model calibration and validation based on regression
analyses.
The model has been employed to project land-use patterns until 2022 as a baseline
scenario. In accordance with recent local urban planning and development discourse the
impact of transport infrastructure projects on the distribution of future urban growth
has been simulated in four scenario settings. The results have been analysed with
reference to the baseline scenario to compare the characteristics of likely urban futures.
The application of the model demonstrates the considerable potential of urban growth
modelling for the situation in Dar es Salaam and its transferability to cities facing similar
conditions. It provides a valuable laboratory to test the drivers and mechanisms of urban
growth and the associated means of intervention. During field work interim results have
proven that the model is able to establish and maintain a discourse among planners and
other stakeholders thus mitigating one of the major weaknesses of urban development
planning - the lack of cooperation and coordination. This is an essential first step for
strategic intervention into informal urban development processes given the limited
resources at hand and to support planning authorities in Dar es Salaam to cope with
future urban development in a pro-active manner.
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Keywords
Africa, cellular automata, Dar es Salaam, informal urban dynamics, megacities, Tanzania, urban modelling and simulation