A megacity in a changing climate: the case of Kolkata Susmita Dasgupta & Asvani K. Gosain & Sandhya Rao & Subhendu Roy & Maria Sarraf Received: 11 November 2010 / Accepted: 4 June 2012 / Published online: 28 June 2012 # Springer Science+Business Media B.V. 2012 Abstract Projections by the Intergovernmental Panel on Climate Change suggest that there will be an increase in the frequency and intensity of climate extremes in the 21st century. Kolkata, a megacity in India, has been singled out as one of the urban centers vulnerable to climate risks. Modest flooding during monsoons at high tide in the Hooghly River is a recurring hazard in Kolkata. More intense rainfall, riverine flooding, sea level rise, and coastal storm surges in a changing climate can lead to widespread and severe flooding and bring the city to a standstill for several days. Using rainfall data, high and low emissions scenarios, and sea level rise of 27 cm by 2050, this paper assesses the vulnerability of Kolkata to increasingly intense precipitation events for return periods of 30, 50, and 100 years. It makes location-specific inundation depth and duration projections using hydrological, hydraulic, and urban storm models with geographic overlays. High resolution spatial analysis provides a roadmap for designing adaptation schemes to minimize the impacts of climate change. The modeling results show that de-silting of the main sewers would reduce vulnerable population estimates by at least 5 %. 1 Introduction The Intergovernmental Panel on Climate Change (IPCC), in its overview of global trends of extreme weather events up to 2006, notes that the frequency of heavy precipitation events has increased over most land areas (IPCC AR4 2007). Historical evidence highlights the dangers associated with such intense precipitation events in developing countries. 1 Flood-related deaths increased steadily from 17,000 in the 1960s to more than 58,000 in the 1990s in developing countries (EM-DAT 2010). Floods affected billions of people who were injured, made homeless, or forced to seek emergency assistance. Recent examples of devastating extreme precipitation impacts in developing countries include the following: floods 2 in Pakistan (1,600 people died Climatic Change (2013) 116:747–766 DOI 10.1007/s10584-012-0516-3 1 Countries identified by the World Bank as Low Income or Lower Middle Income. 2 http://www.dartmouth.edu/~floods/dbtop.html, accessed December 2011. S. Dasgupta (*) : S. Roy : M. Sarraf World Bank, MC3-347, 1818 H Street, N.W., Washington, DC 20433, USA e-mail: sdasgupta@worldbank.org A. K. Gosain Department of Civil Engineering, Indian Institute of Technology, Delhi, India S. Rao INRM Consultants Pvt. Ltd., Delhi, India