Duration of heatwaves to get longer in 189 Indian cities, says study
Kolkata will see the highest increase in heatwave frequency and durations with 5.4 heatwaves predicted per year
On average, 189 Indian cities will see the duration of the longest heatwave of the year get longer by 61% to 24.1 days at 3°C compared to 15 days at 1.5°C scenario, according to a research paper published on Thursday.
The study by the World Resources Institute’s (WRI) Ross Center for Sustainable Cities and supported by Bloomberg Philanthropies also said the number of heatwaves per year will increase from 4.1 days to 5.3 days with a corresponding increase in warming.
The research findings are based on a downscaled global climate model (NASA Earth Exchange) covering 996 cities. WRI said with over two-thirds of the world’s population expected to live in cities by 2050, new global data on the 1,000 largest cities provides a granular view into potential climate futures — highlighting growing hazards and the urgent need for climate adaptation investment “This new statistical modelling method can make it easier to predict city-scale impacts from global data and points to the urgency for even more granular modelling work to enable cities to prepare for the worst effects of climate change and rally to reduce emissions faster,” the statement added.
The 1.5°C warming threshold was established in the Paris Agreement 2015 to limit the increase in average global temperatures and minimise the impact of climate change due to a rapidly warming earth.
The change in heatwave days would also mean that the cooling demand will increase by 13% across India when measured in cooling-degree days if the warming is not restricted to a 1.5°C level, according to the same research. Cooling-degree days are calculated in the number of degrees that a day’s average temperature is above 18°C.
In another finding, the researchers said the changed 3.0°C scenario will also see the number of days optimal for malaria-transmitting mosquitos to reduce across India primarily in the north and east with increase in most cities in central and south India, according to the research findings. For example, peak malaria days would reduce from 221.3 days in 1.5°C level to 153.9 days at 3°C level.
Going by their estimates, Kolkata will see the highest increase in heatwave frequency and durations with 5.4 heatwaves predicted per year at a 3°C scenario compared to 2.7 such periods at a 1.5°C scenario. The longest heatwave days are expected to go up to 23.9 days from 9.5 days with the corresponding change in temperature. In other cities, such as Delhi, Chennai, and Hyderabad too, the trend is similar with heatwave frequency predicted to increase between 0.5 to 1.1 days and the duration of the longest heatwave to increase between 1.9 to 3.7 days at a 3°C scenario as against 1.5°C level.
Interestingly, Bengaluru is expected to see a dip in heatwave frequency to 3.8 heatwaves compared to 4 in a year at 3°C scenario from 1.5°C level. However, the duration of the longest heatwave in the year is set to increase to 37.8 days from 13.5 days with the corresponding rise in global temperature. A similar trend is predicted for Ahmedabad where the frequency of heatwave goes down marginally but the longest heatwave duration increases. Contrastingly, Mumbai which is expected to see a higher frequency of heatwaves by less than a day in a year (0.8) will see the duration of its longest heatwave going down marginally to 15.1 days at the 3°C level from 16.8 days at 1.5°C level.