Dhaka—like other rapidly urbanising megacities in the tropics, is facing overwhelming demand for buildable land, which continues to surpass needs for urban open space. Such a pattern of development resulted in a dense urban fabric. For urban designers, architects and planners, efforts in providing spaces for the community has become a challenging task—more so due to a very complex dynamics of rapid and uncontrolled urbanisation, an understanding of which has become imperative for the future design professionals. Added to this ambivalent urbanisation in a developing context, extreme disaster events such as an earthquake pose a serious threat in terms of loss of lives and property. According to the earthquake disaster risk index, Dhaka is placed among the twenty most vulnerable cities of the world. How an urban designer reacts to such information while designing for building or city scale development seems to be a prime concern for future Dhaka.

The recent earthquakes in Dhaka have already given us a wakeup call and made people more concerned about the post disaster preparedness and safety issues. Given the fact that earthquakes cannot be prevented or sensed early-on and that actually the collapse of buildings and lack of infrastructure cause death and destruction, certainly makes such an extreme event a part of the urban design agenda. The existing urban trends and unplanned urbanisation process in Dhaka results in high population density as well as built environment. These urban trends increase vulnerability to natural disasters like earthquake due to the concentration of people and assets. This sort of dense development is a serious threat to any earthquake evacuation planning by hampering accessibility at local and global level of the city.

Old Dhaka, the historic core of Dhaka city is an extreme example of such a dense and unplanned development, developed within a process of spontaneous growth. It represents physical earthquake vulnerabilities like high population density, informal or unplanned settlements, non engineered buildings and shelters, large number of poorly built buildings, contiguous building pattern and lack of open spaces add up to the problem. All these have created inaccessibility of movement at the building block and street level, which will make any post disaster management even worse.

From this view point, an effective evacuation planning to mitigate earthquake vulnerability in Old Dhaka is urgent to reduce the losses. To understand the situation, a research has been done in the recent past at BUET, titled 'Earthquake Vulnerability Reduction Strategies for Unplanned Urban Areas'. The research selected Old Dhaka as the study area representing an extreme case of physical vulnerability. As a densely populated area, wards 71 and 74 have been taken as the study area [Fig:1]. The aim was to develop an accessibility network model to help the future planning process in earthquake rescue and recovery.

The study investigated spatial organisation of street network to understand and design level of accessibility [Fig:2] to enhance post disaster management in Old Dhaka. The study identified street hierarchies considering their connectedness to local and global surroundings, road width and density of the urban fabric along these streets, using evidence based approach through GIS and field survey for old part of the city.  Further people's movement pattern and density has been counted to see the relation between street hierarchy and actual pattern of movement. Peoples choice of local and global streets within and between mohollas or communities seems to be an interesting finding to identify the usable streets in reality, which strongly correlated with the street category identified in terms of their spatial connectivity.

Figure: 1 3D image showing the density of wards 71, 74 and its immediate surroundings (Source: unpublished Report: Earthquake Vulnerability Reduction Strategies for unplanned urban areas - in the context of old Dhaka, 2011).

However, accessibility also refers to safe shelter within a close proximity to the vulnerable areas.  After a major earthquake, the open space network in the city such as parks, play fields, green tracts etc. serves multiple complex functions such as post disaster shelter, gathering of people, distribution of goods and services, temporary inhabitation etc.  A designed network of open space not only significantly contributes to the quality of everyday urban life, but also has the latent capacity to facilitate quick post disaster recovery in unplanned areas. Therefore, the study also explored the accessible network of open space in the area to understand how to ensure and design a safe evacuation planning as part of post disaster management. This led to a new level of understanding of the possibilities of urban safety leading to sustainable evacuation planning in densely developed local areas of Old Dhaka.

Most naturally, the study found a serious scarcity of open space in Old Dhaka. The common pattern of open space distribution showed a concentration of few green open parks in a specific locality but the rest of the area has no open space at all. Therefore, alternative options were being searched. Therefore, in the dense study area public buildings were also considered as evacuation shelters. Interestingly the study identified many public buildings like primary and high schools, training centres, mosques, hostel, temples, community centres, etc. and some open spaces like playgrounds, graveyards and water bodies. In absence of adequate open spaces for shelter, these open spaces in and around the public buildings could be easily adopted as shelter during an extreme disaster event like earthquakes. Before suggesting these public buildings and open spaces as a post disaster shelter, an assessment of their structural vulnerability has been checked and suggested for retrofitting where necessary, to prevent further loss of life.

For an unplanned city like Dhaka, it is crucial to develop an accessibility network model of urban street and open space system to ensure a safe and rapid evacuation as part of post disaster management strategy. The research showed that an accessible street network based on people's movement pattern and density and other morphological aspects such as land use, building density and distribution of public open space and shelter appeared to be a starting point for effective rescue and recovery planning. The proposed ideas may further impart awareness among the future design professionals, planners and urban designers to ensure a resilient city. A designed accessibility network would promote earthquake awareness including preparedness and mitigation programs within the community. A pre-planned evacuation plan for a locality would make them self-dependent in facing a disaster and enable them to cope with the adverse situation. A place-specific or contextual integrated evacuation plan seems essential for each and every locality in unplanned cities like Dhaka. Local accessibility of street network, existing public buildings and open spaces would ensure a prompt and safe evacuation during a disaster and thereby reduce earthquake vulnerability of an unplanned city like Dhaka.

The author is professor at the Dept of Architecture, BUET. Her fields of interest include urban morphology, and disaster management at city scale