Floods to frequent Chennai as rainfall may double in 60 years

After remaining relatively consistent over the decades, the climate in Chennai – both temperature as well as rainfall – is likely to be erratic in the remaining decades of the century, with the maximum levels going up substantially, warned a future climate scenario that looked at the future till 2100.

Three years ago, Chennai recorded a rainfall – and flood – so heavy that it entered the pages of history. That year, the city witnessed seven heavy rainfall events – more than 60 mm rain on a single day. But if experts are to be believed, this is likely to be more common in the coming decades, making it imperative on the authorities to make action and response plans.

According to the monthly data that the Meteorological Department develops jointly with the Indian Institute of Tropical Meteorology, Pune, the mean annual rainfall for Tamil Nadu is 928 mm (based on data from 1871 to 2016). The worst was in 1952 (only 627 mm) and the maximum was in 2005 (1,272 mm).

When analysed, the data from 1951 to 2014 showed that the temperature in the city went up by 1.7 degrees Celsius of temperature, an annual increase of 0.03-degree Celsius. “It is also found that the mean annual and summer temperatures are rapidly increasing,” says Lakshmi Kumar TV, assistant professor (research), Department of Physics Atmospheric Science Research Laboratory, SRM Institute of Science and Technology.

Lakshmi Kumar had recently participated in an international conference organised by National Oceanic and Atmospheric Administration (NOAA), US department, The Energy and Resources Institute (TERI) and Indian Meteorological Society. Using the data shared by the experts in the event, Lakshmi Kumar prepared the future climate scenario of Chennai till 2100.

The information includes annual cycle of average and maximum temperatures for different periods, maximum temperature of the hottest days between 2018 to 2100, yearly rainfall cycle in different periods and the number of heavy rainfall events from 2018 to 2100.

According to him, the average annual rainfall over Chennai, which was around 1,400 mm during the period 1980 to 2009, is expected to increase in the coming years.

The annual rainfall in the period from 2010 to 2,039 is estimated to be 2,246 mm. This is expected to climb to 2,417 mm in the period between 2040 and 2079, and then to 3,606 mm during the 2080 to 2100 period.

In the 15 years from 2001 to 2015, heavy rainfall events were recorded as many as 45 times. But this is likely to double in the coming decade (2018-2028), he said. This increase, Lakshmi Kumar said, would be recorded mainly in June, October and November – the last two falling within the primary rainy season for the state.

From the record seven heavy rainfall events that led to the devastating floods in 2015, the city might witness even 20 such events a year, warned the data he prepared.

A similar trend is seen even in the case of temperature, said the research paper. The maximum temperature is feared to increase substantially – possibly touching even 5 degrees Celsius above the present record by 2100. The number of summer days will also be extended, with temperatures remaining high even in June, a month after the present peak summer period.

Just like rainfall, the maximum temperatures are also likely to increase in the future. The average maximum temperatures could go up by 4 degrees Celsius between 2010 and 2039, touching 4 degrees Celsius (2040 – 2079) and 6 degrees Celsius (2079 to 2100).

Thus, the average day time temperature in May and June could reach 43 degrees Celsius as per this calculation. Maximum temperature may hover around 47 degrees Celsius in the next decade and half, and cross even that mark by the second half of the present century.

An analysis by the Regional Meteorological Office (RMC), Chennai, of the weather data from March, April, May and June showed an increase of 1.8 degree Celsius in the mean temperature in March – the average temperature that was 32.2 degree Celsius in March 1906 has risen to 34 degrees Celsius now.

Also, in the past century, mean temperature in April has risen from 34.1 degree Celsius to 35.6 degrees Celsius. But mean temperatures in May and June remained constant at 36-37 degrees Celsius.

“There will be periodical change in solar radiation that may bring clouds and raise temperature,” said retired deputy director general of Regional Meteorological Centre Y E A Raj, pointing out how many international studies have indicated about the climate change that is in store. Another former Deputy Director General of Meteorology, Chennai, R V Sharma, added that studies had projected sea-level rise of up to 0.8 meters by 2100.