Urban floods have become too common phenomenon in Indian cities. Reasons are many, ranging from lack of urban planning, information availability in open domain etc. Whatever be the reason the loss due to these climatic events is huge. All major cities in India Mumbai,Chennai, Gurugram, Bengaluru and Hyderabad have faced nature's fury at one time or another. In this blog we will try to figure out what can be done to minimize the effect of floods.

Unplanned Buildings

Man made obstructions like roads and buildings to natural streams which link the tanks are major cause of urban floods. Due to climate change sudden cloud bursts are also causing havoc.

Buildings (Shown In RED) in Natural streams : background source Bing Maps
Buildings (Shown In RED) in Natural streams : background source Bing Maps

Image shows that there are buildings built in the streams creating obstruction to water flow. The blue pixels are presence of water during rains (picked from Landsat Imagery). Channels are extracted using ASTER data. These datasets show that there is a channel with water in this area and buildings are constructed right on the channel.

These are some challenges which are very difficult to overcome given the current economics prevailing in India. If we leave what has happened behind, if this challenge of unplanned buildings have to be prevented there needs to be more data available in open domain. This helps both buyers and builders in urban real estate market to plan their activities.

Information Availability

Land records availability is also a challenge. National Land Records Modernization Program is to bring in transparency in land records in India. This information helps in knowing about legal aspects such as title deeds of the land. But lack of information about water bodies, terrain etc in public domain is a very big challenge. This is also required to be put in public domain. This helps (those handling real estate transactions) in better planning their sales and purchases.

When you Buy a house
When there is no flood everything looks good.
When there is a flood
When there is a flood

When there is no flood, the terrain especially in non coastal Indian cities like Hyderabad, Bangalore or Pune looks dry. Lack of water body or terrain information to buyers/builders leads to unplanned constructions. The image below shows huge townships ending up in water during flood.

Effective use satellite data helps in visualizing the terrain. For example the same 2D satellite image when overlaid on elevation data and visualized in 3D looks like this. This map helps any common man to understand that the buildings shown are in a valley and are prone to flood.


Buildings in flood zone
Buildings in flood zone - Blue showing water spread during dry season and red during a flood.

How to address these challenges

NASA updates some of its satellite data  on daily basis. Terrain information is available for entire country in Bhuvan. Openstreetmap data gives other information such as roads, atms etc. All these can be combined to do a feasibility study before coming up with a construction activity.

These open datasets and tools like QGIS, gvSIG help

  • Banks and Insurance agencies to come up with a risk matrix for their areas of operations.
  • Organizations to do a feasibility study before taking up construction activities or procuring land.
  • NGOs/housing societies/educational institutions to use this data and tools to educate citizens.
Urban Floods
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