The experiential impact of climate change is becoming an usual occurrence day by day. Incidents ranging from waterlogged roads, flooded airports and building collapse are becoming frequent and common experiences in our cities. While this can be viewed as temporary disturbances emerging from climate change, the loss of lives and direct economic losses resulting from such incidents are significant, writes Vaishnavi T.G. Shankar, Lead-Training & Capacity Building, Climate Centre for Cities, NIUA.
India experienced 85 floods between 2009 and 2020 that affected over 10 crore people and resulted in 17,540 fatalities along with estimated damages of approximately $58 billion¹. The 2005 flood in Mumbai resulted in 500 fatalities and an economic loss of $2 billion². Such fatalities and economic losses are likely to increase with the projected severity and frequency of climate disasters in India, particularly heat waves and heavy precipitation in urban areas as per the Intergovernmental Panel on Climate Change (IPCC) ARC 6 Report. While the country is expected to spend $1.4 trillion on infrastructure development by 2024-25³, the emphasis on building climate resilience to safeguard investments cannot be greater. While in all this, strengthening the resilience of cities, protecting the lives of people and improving the quality of life is indispensable. With the example of buildings, this article illustrates the flood risk to losses and damages along with a way forward for making buildings flood resilient.
Urban floods and buildings
Flooding in cities occurs due to heavy rains, swelling of rivers and inundation of coastal areas due to storm surge or high tides. While the latter two have historic patterns of floodplains, unplanned urbanisation and expansion into floodplains can result in severe flooding. Besides, obstruction to the natural drainage due to dense construction in cities coupled with a limited or no drainage network can lead to urban flooding.
The number of severe urban floods as shown in Fig.1 illustrates an increasing trend in the last few years. The experience from these floods have revealed the immediate risk of loss of lives from drowning, landslides and building collapse besides damages to properties. Between 1953 and 2004, India’s average value of flood related damages to houses was ₹251 crores. This significant value of damages illustrate the vulnerability of our buildings to floods⁴.
Buildings with shallow foundations and walls built of mud blocks, bricks or stone masonry with mud mortar are watersoluble and are at high risk for damages from floods⁵. Assessing the Census 2011 data for Smart Cities illustrate that 19 cities and 5 cities experiencing either pluvial or fluvial flooding have 20-35 per cent and 40-65 per cent of their households vulnerable to building damages respectively. The majority of the houses have walls built with unburnt bricks or stones that are not packed with mortar. Hence, making them vulnerable to damages during floods. While the vulnerability of a building is not limited to the type of wall construction or the materials used, the illustration of this one aspect of vulnerability reveals the extent of flood risk in buildings. The collapse of a wall or the building is of greater risk as this may result in loss of lives, however, damages can also lead to significant expenditure on repairs. A study from the 2005 floods in Mumbai revealed that the largest amount spent by flood-affected people were on house repairs⁶.
Flood resilient buildings, a way forward
A significant share of post-disaster recovery funds is usually allocated to housing⁷. This indicates that buildings experience maximum damages from disasters and that there is a pressing need to ensure we have resilient buildings to mitigate disaster related losses and damages. The main reason for disaster vulnerability of buildings is inappropriate options for housing along with poor construction⁸. Poor construction of houses is directly linked with the choice of materials used either due to lack of affordability or the understanding of its performance in various geo-climatic conditions and hazard zones. Addressing these challenges is key for strengthening the flood resilience of buildings and the following measures provide a way forward for our cities.
Mapping for informed decision making:
The location of storm water drains is crucial for mitigating flood risk in a city. Developing a terrain map will be beneficial to inform the appropriate location and construction of storm water drain network. This map will also help identify the essential natural drainage in the city where construction can be prohibited.
Identifying existing vulnerable buildings and retrofitting them is an important step to reduce flood related losses and damages. To inform this, a flood hazard map marking river catchments, flood plains, flood pathways, water bodies such as canals, lakes etc, and low lying areas needs to be developed and accordingly, dilapidated buildings and buildings in the low lying areas can be mapped. The flood hazard map also informs relevant guidelines and regulations that needs to be integrated within the master plan, land use plan, building bye-laws and Development Control Regulations (DCR). For instance, prohibition of construction in the flood plains and old water bodies, and specific bye-laws for construction in vulnerable areas etc,. Further, understanding the flood risk for various return periods (5 years, 10 years and 50 years) and mapping them spatially can guide the course of infrastructure development and construction in cities. This is keep for developing forward looking and resilient cities.
Building byelaws and construction: 5 states have explored the light house projects under PMAY-U and built housing projects considering the geo-climatic and hazard conditions of the region. There is great potential to scale up this effort across the country to climate proof housing projects.
In circumstances where construction in flood prone areas is unavoidable, the building’s plinth level should be 0.6 metres above the drainage or flood submersion lines. Also, buildings should preferably have more than 2-storeys as the higher floor can be used as temporary shelter during a flood. These guidelines recommended by the National Disaster Management Authority for flood management needs to be incorporated within building bye-laws and effectively implemented by cities. Importantly, the provisions of the Model Building Byelaws for risk classification of buildings and climate resilient construction needs to be implemented across the cities for enabling a transformation in the building construction ecosystem.
Capacity building, awareness and local actions: Building Materials and Technology Promotion Council has initiated capacity building of the construction work force around disaster vulnerabilities, flood resilient and cyclone resistant housing. Strengthening this approach with much more aggressive awareness campaigns and training will be beneficial.
There are various examples of community driven or architect driven construction of flood resilient buildings using indigenous solutions. For instance, numerous local architects in Kerala are adopting a combination of local materials such as bamboo, mud and concrete to build flood resilient houses. Building on stilts that raise the floor and solutions such as pre-fabricated and pre-stressed houses are also being explored. Coupled with the active awareness campaigns on flood resilient housing by the Kerala State Disaster Management Authority, more people from the vulnerable hotspots are embracing such construction.
A combination of spatial mapping to inform planning; incorporating flood resilient measures in master plans, land use plans, building bye-laws and DCRs to guide resilient development; mandating provisions of Model Building Byelaws to promote the construction of flood resilient buildings; building the technical capacity of construction work force on disaster resilience and sensitizing people living in vulnerable hotspots to opt for flood resilient housing can pave the way for strengthening resilience and reducing the building risk to losses and damages.