Addressing policy challenges from Chennai’s 2015 extreme rainfall event

This policy brief examines the extreme rainfall event in Chennai on 1 December 2015, which saw a record 494 mm of rain in 24 hours. While climate attribution studies concluded the event was not caused by anthropogenic global warming, the document highlights how unplanned urbanisation and poor infrastructure exacerbated the disaster's impact, costing the Indian economy an estimated US$3 billion.

• The extreme rainfall event in Chennai on 1 December 2015 was not caused by human-induced climate change. Scientists used multiple peer-reviewed attribution approaches to conclude that the event was not attributable to anthropogenic global warming.
• The 2015 event was exceptionally rare, with a return time estimated between 600 and 2,500 years. The probability of such an event occurring at any given weather station is less than 0.2% annually.
• Contrary to global trends, sea surface temperatures in the western Bay of Bengal have not risen over the last 35 to 40 years. This lack of warming is attributed to the 'brown cloud' of air pollutants (aerosols) that block sunlight and cool the surface.
• The disaster's impact was worsened by systemic urban failures, including the non-protection of wetlands, inadequate flood-zone planning, and massive encroachment of lakes and riverbeds for construction. Additionally, the city's storm water drains were non-functional and outlets were clogged due to a lack of timely desilting.
• The 2015 rainfall event resulted in an estimated cost of US$3 billion to the Indian economy and left over 2.6 million houses in low-lying areas submerged, with those in informal settlements being the most vulnerable.
• To build urban resilience, the document recommends protecting urban wetlands, adopting a river basin approach for flood-zone maps, revising building codes to include water-harvesting, and creating city-specific flood action plans that prioritize the most marginalized populations.

APA

Climate and Development Knowledge Network (2017). Addressing policy challenges from Chennai’s 2015 extreme rainfall event. https://cdkn.org/sites/default/files/files/CDKN_RRA_ChennaiFlood_PB_Pr1Final_WEB.pdf

Chicago

Climate and Development Knowledge Network. Addressing policy challenges from Chennai’s 2015 extreme rainfall event. 2017. https://cdkn.org/sites/default/files/files/CDKN_RRA_ChennaiFlood_PB_Pr1Final_WEB.pdf.

Wikipedia

{{cite report |author=Climate and Development Knowledge Network |title=Addressing policy challenges from Chennai’s 2015 extreme rainfall event |date=2017 |url=https://cdkn.org/sites/default/files/files/CDKN_RRA_ChennaiFlood_PB_Pr1Final_WEB.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{climateanddevelopmentknowledgenetwork2017addressing, author = {{Climate and Development Knowledge Network}}, title = {{Addressing policy challenges from Chennai’s 2015 extreme rainfall event}}, institution = {Climate and Development Knowledge Network}, year = {2017}, url = {https://cdkn.org/sites/default/files/files/CDKN_RRA_ChennaiFlood_PB_Pr1Final_WEB.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }