The city is no stranger to flooding. In 2007, a Drescher et al. study on risk perception consisting of analysis of flood risk exposure and the development of flood risk maps showed that flooding is a regular occurrence. The study documented a total of 26 floods from 1943 to 2006 and noted a sharp increase in the number of flooding events from the 1970s. Before this could be categorized as a direct correlation of climate change, the study also highlighted, based on the meteorological data from 1813, that there has been no increase in the rate of rainfall received annually over the years. Floods of 1996 and 2005 had been caused by strong single rainfall events exacerbated by manmade pressures. (Vencatesan,2021)
Care Earth Trust has been studying the cyclical nature of Chennai floods and droughts, and the trend shows heavy flooding once in 10 years. However, with the 2021 floods, this periodicity has reduced to six years.
Over the years, the trend of losing wetlands and forested areas to built-up space continues. Unlike the lakes and reservoirs, the wetlands are not even enumerated, and they are the ones facing either total loss or land fragmentation. Similarly, in the green areas, the reserve forests have remained stable in their area, but the orchards and paddy fields have disappeared. The city is losing its wet character; losing its character to handle water. From a policy perspective, Chennai is always planned itself as a dry city whereas in reality with an average annual precipitation of 1428 mm, it is not a dry city. The other factor that is also missed out in the planning process is that Chennai is a coastal city.
During the 2021 floods, Care Earth Trust used crowd-sourced data to map the areas flooded at a granular level. More than 400 water-logged areas have been mapped using data collected from the news, videos of water-logged locations, geotagged photographs, and crowdsourced information through forms shared on social media. This information was used in Geospatial technology to depict the spatial pattern of waterlogged areas. It is easier to understand the implications of strategy in terms of preventive measures when information is visualized spatially. This allows for scientific planning with affecting parameters such as land topography, historical state of waterbodies, and urban drainage system to create a mitigation to reduce the impact of future flooding.