Green roofs can help reduce flooding in densely populated urban areas, says a study by IIT B, a study by CEPT University.

Mumbai, Oct 31 (PTI) Planting small trees on the roofs of buildings in densely populated areas can reduce flooding in large and densely populated cities, according to a study jointly conducted by CEPT University Ahmedabad and Indian Institute of Technology Bombay (IIT Bombay). ).

As the number of buildings, pavements and roads made of concrete or resin increases, water-absorbing areas on the ground decrease, leading to urban flooding and waterlogging in low-lying and densely populated urban areas after heavy rainfall, the report said.

Implementing small-scale distributed measures such as rainwater harvesting, rain gardens and green roofs help reduce flooding and control runoff closer to its source, the study notes.

According to the study, green roofs are created by planting trees on the roofs of buildings in a shallow layer of soil above a waterproof membrane and drainage system.

Green roofs can keep a building cooler in the summer and absorb rainwater, and excess water can help slowly recharge a rainwater harvesting system, avoiding rapid runoff, the report notes. Installing a green roof requires additional costs and increases the weight load on the building, as well as requiring regular maintenance.

However, not all buildings in India are suitable for green roof installation. The study notes that slums and some low-cost houses with metal roofs or concrete sheets are not suitable for green roof installation.

“The significant contribution of the study is that it provides a realistic assessment of performance in a dense urban area and quantifies runoff reduction. These inflated estimates arise from scenarios that consider all roofs without assessing green roofing potential,” said CEPT University faculty. Tushar Bose and IIT B professors Pradeep Kalbar and Arpita Mondal.

The study also found that the use of green roofs could reduce flood volumes by 10 to 60 percent depending on the percentage of green roofs applied during higher than normal biannual rainfall.

However, the reduction is not linearly proportional to the application rate because the volume of floods also depends on the capacity of the drainage network, especially when rainfall volumes are high, the report said. Researchers have observed that when fewer than 25 percent of buildings have green roofs, the reduction in flood and runoff volumes can be as low as 5 percent.