- Though Pune has not experienced a specific trend in rainfall during the last four decades, there has been a marked increase in years with days of heavy rainfall.
- While there is no conclusive evidence yet, globally, on climate-driven changes in the frequency and magnitude of floods, regional changes in rainfall, such as what Pune has been witnessing, could lead to floods.
- Recognising the various dimensions of the vulnerability of cities, allows us to take concrete steps towards making our cities resilient to impacts of extreme weather, anthropogenic or otherwise, write the authors of this commentary.
- The views in this commentary are that of the authors.
In September 2019, Pune city, in India’s western state of Maharashtra, witnessed heavy rainfall and unprecedented flooding. There was widespread destruction of property and loss of lives. Researchers, civil society groups and general public were quick to point to several potential factors including rampant urbanisation, changes in land use and lack of planning that led to the floods. A common thread in many of these debates was imminent climate change resulting in the floods. It was argued that the city might see changing weather patterns and more floods in future. As Pune enters another monsoon season, we ask the question how likely is this to be the case?
We looked at rainfall patterns in Pune during the last 42 years (1978-2020) in detail using daily rainfall values obtained for the city’s Shivajinagar observatory, from the HadISD dataset.
The annual rainfall in Pune city during the last 42 years (Figure 1 a) shows that the mean June-October rainfall during the period was 852.5 mm (dashed red line). While there is significant year-to-year variability during these four decades, no trend in the monsoon rainfall has been observed. The seasonal accumulation during 2019 was not exceptional over this period either, though it is interesting to note that 2019 was preceded by eight years of average or below average rainfall, which has never been observed before.
Daily extremes in rainfall, especially during the peak rainfall season, is a better indicator of flooding than annual rainfall. Therefore, we computed the 95th percentile of daily rainfall for each year (Figure 1 b). In contrast to the seasonal accumulation, years that experienced heavy rainfall episodes seem to be more frequent over the past 20 years. There have been nine years between 2000 and 2020 which have a 95th percentile of daily rainfall greater than 40 millimeters as compared to four years during the period between 1978 and 2000. In 2019, while the seasonal accumulation was not exceptional, the extreme values of daily rainfall are among the highest observed during these 42 years.
Does this mean that Pune city will see more flood events comparable to 2019 in the coming years?
Our analysis clearly shows that although Pune has not been experiencing a trend in rainfall during the last four decades, there has been a marked increase in years with days experiencing heavy rainfall. Such heavy rainfall is more likely to cause flooding. Indeed, the devastating floods in 2019 were triggered by heavy rainfall that happened over three days beginning 25th September. Our analysis is based on data from just the Shivajinagar observatory and therefore our results are likely to be representative of the situation in the inner city than the suburbs. Nevertheless, this is indicative of how rainfall has been changing over the last four decades in the Pune region.
The Mula-Mutha basin and Pune city have witnessed huge transformation in land use over the last three decades. Built-up area has increased from 32% in 1990 to 48% in 2019. In 2015 the city disaster management plan had identified the wards that were at risk of floods and flash floods and outlined several mitigation measures. Stormwater system in the city has not kept pace with its expansion and encroachment has resulted in the decrease in width of rivers and increase in the number of potential flash flood points in the city. The Pune Municipal Corporation itself acknowledged the role of encroachments in the 2019 floods. The civic body had initiated an anti-encroachment drive and construction of retaining walls in the flood zone, particularly in the worst affected Ambil Odha. However, a lot more remains to be done.
Extreme events and natural disasters are frequently attributed to climate change, and the debate around floods in Pune has been no exception. Rainfall is but one aspect of climate change. There is no conclusive evidence yet globally on climate driven changes in the frequency and magnitude of floods. Nevertheless, regional changes in rainfall such as what Pune has been witnessing could lead to floods. There is increasing evidence from recent studies that such floods induced by extreme rain events have been on the rise in Central India.
Climate change has become a rallying point for global environmental action, and rightly so. However, at the scale of a city, climate change can easily become a straw man to maintain status quo, suggesting helplessness against natural forces that one does not have control over. This can obscure the multiple stressors that cities and urbanising basins face and also the role of human interventions such as the ones that we noted above in exacerbating flood risk. Recognising the various dimensions of vulnerability allows us to take concrete steps towards making our cities resilient to impacts of extreme weather, anthropogenic or otherwise.
The authors are with the Centre for Water Research, Indian Institute of Science Education and Research (IISER) Pune. Ayushman Singh is an M.S. student, Joy Merwin Monteiro (climate scientist) and Bejoy K. Thomas (social scientist) are faculty members.
Banner image: Vehicles wade through the waters on the flooded banks of Mutha river during the rains of July 2007. Photo by Shankar S./Flickr.
