Using GIS and other methods to understand and quantify the vulnerability of a megacity like Mumbai to floods

In the last week of July, 2005, Mumbai, the megacity on the western coast of India, was pounded by hours of torrential rains of a magnitude and intensity not seen in living memory. The resulting floods brought the vibrant metropolis, which prides itself on being “on the go” 24/7, to its knees. Infrastructure was overwhelmed. The administrative machinery of the state, caught completely unprepared, was left powerless to cope. Damage to property was estimated at $2 billion. Although 500 people lost their lives, that number would have been much higher but for the guts, grit and spirit of the people of Mumbai.

In hindsight, Mumbai has always been a disaster waiting to happen, given the presence of several factors that make for very high flood hazard. For one, Mumbai sits on the western coast of India, which sees high orographic rainfall during the annual monsoons. For another, situated as it is right on the sea, the city is affected by tides. Further, Mumbai is hemmed in by hills on the eastern side, which catch the rain and funnel the water towards the city.

The city is built on reclaimed land, and as a result some areas of it lie as low as 10 meters above sea level and less. To compound all the above factors, the ever-growing population of this overcrowded city just doesn’t have enough space to live in. As a result, encroachment is rampant and this has led to the blocking of the natural channels which used to drain rainwater.

Surprising, then, that till the big flood of ’05, there had been no studies to assess the flood risk to Mumbai. Shocking that, all these years after the flood, there still is no flood risk map for the city. It is against this background that the work done by Sherly M. A. stands out.

A research scholar at the IITB-Monash Research Academy, Sherly has created a framework that is more comprehensive than all those employed so far in studies on flood hazard. Although recent years have seen a growth in the volume of quality research on urban flood risk, most of these studies tend to miss the forest for the trees. The reason is that most of them approach the problem from one perspective or other, rather than attempting to see the big picture.

Technocrats tend to a look at the issue in terms of topography and infrastructure, whereas social scientists are more concerned with the socio-economic and human angle. An effective flood risk map, however, requires a multi-disciplinary approach with inputs from policy makers, social scientists, engineers and the general public. Sherly’s work gives equal importance to both engineering and social aspects of flood risk.

The purpose of a flood risk map is to assess and map the hydrologic, hydraulic, socio-economic, infrastructural and spatial-temporal elements that contribute to flood risk and vulnerability. Due to rising urban populations worldwide and increased rainfall due to climate change, more and more people are vulnerable to the dangers of floods. Against this backdrop,flood risk maps gain importance as an essential tool for urban planning, infrastructure creation, disaster relief and recovery.

Sherly’s method for creating a flood risk map involves two steps, each creating one component of the map. The first, a flood hazard map, is generated using flood modeling, taking into consideration the combined effect rainfall and tide. The second, a flood vulnerability map, is generated by two types of vulnerabilities, infrastructure and socio-economic.

The two types of vulnerabilities are first evaluated individually. Infrastructure vulnerabilities are assessed in terms of the possible extent of inundation of a) critical facilities such as hospitals, public buildings, emergency shelters, schools, etc and b) of emergency services such as fire stations, ambulances, police stations, etc.

All this information, aggregated in a Geographic Information System (GIS) environment, is combined to create the Flood Risk Map. Presenting all the aspects of the risk from floods within an integrated framework would be of immense use to decision makers. It will help them create land development plans, land zoning laws, emergency response strategies, disaster recovery, and infrastructure development etc.

Working under the guidance of Prof. Subhankar Karmakar of IIT Bombay, Dr. Terence Chan of Monash University and Prof. Christian Rau of Shantou University, the research team hopes to have a demonstration version of the flood risk map ready by the end of 2014.

Asked about her motivation to research the subject in such depth, Sherly says, “Water is the source of all life, but it has the power to destroy as well. This paradox has drawn me to hydrology as early as my undergraduate years. I see at as means to contribute, in my own humble way, towards ensuring that humanity is spared the destructive power of water”

IITB-Monash Research Academy is a Joint Venture between IIT Bombay and Monash University. Research scholars study for a dually-badged PhD from both institutions, and enrich their research and build collaborative relationships by spending time in Australia and India over the course of their degree. Established in 2008, IITB-Monash Research Academy aims to enhance scientific collaborations between Australia and India.

Research scholar: Sherly M. A., IITB-Monash Research Academy

Project title: IUsing GIS and other methods to understand and quantify the vulnerability of a megacity like Mumbai to floods

Supervisors: Prof. Subhankar Karmakar, Dr. Terence Chan, Prof. Christian Rau

Contact details:

For more information and details on this technology, email research@
The above story was written by Sandhya Menon based on inputs from the research student and IITB-Monash Research Academy.