The occasional spells of rains have brought some relief to Chennai. But that should not cloud the fact that the city went without any significant rainfall for about 200 days at a stretch. Rainfall patterns have become erratic in Chennai, with a spike in extreme weather events such as cyclonic storms and heat waves. Even though a large number of people — in civil society as well as in the government — are sceptical about attributing it to climate change, scientists do feel that there is a strong connect.
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Citizen Matters Chennai spoke to Dr V Selvam, former Executive Director and Lead – Coastal Systems Research** at the M S Swaminathan Research Foundation, about the fluctuations in Chennai’s rainfall pattern and how it is linked with microclimate.
There has been a visible change in Chennai’s rainfall pattern. Convectional rains that occur in summer have become rare, and this time the city has seen 200 dry days at a stretch. Is climate change behind this?
Chennai is blessed with three types of rainfall — rains from the Southwest and North East monsoons and convectional rains. An analysis of 50-year-old data suggests that both the monsoons are variable and non-trend setting. Convectional rains bring 15 to 20 per cent of the annual rainfall to the city during the summer months. But there has been a significant reduction in such convectional rain in Chennai. The data from 1970 to 2000 suggests that the annual average convectional rains have seen a reduction of 3 to 7% in Chennai.
We can attribute this to the change in Chennai’s microclimate. Microclimate is the climate of a small geographical area, and is dependent on land use pattern. For example, localities with rich greenery are conducive for rainfall. Increase in high rise buildings and deforestation, which also contribute to climate change, are the reasons behind the reduction in convectional rainfall. Reflection of heat from high rise buildings prevent the process of evaporation and condensation. Trees cool the upper layer atmospheric temperature, which is again important for convectional rains.
We often hear of sea level rise (SLR) in connection with climate change; tell us how it affects Chennai, if at all?
Sea level rise is certainly a reality in Chennai. But, it has been better (less) compared to the global average sea level rise which is 3.2 mm. In India, it varies from coast to coast. In the northern part of the Indian Ocean, SLR is as high as 4.6 mm per year. In comparison, tidal gauge data at Chennai port indicates an average sea level rise of 0.3 mm per year.
When it comes to SLR, do we have reliable data at all?
In 1850, the British had installed tide gauges at major ports such as Mumbai, Chennai and Kolkata. The tide gauge is an equipment used to monitor the sea level. The Department of Environment, Tamil Nadu is particular about preparing plans for climate change but a lot needs to be done. Tide gauges should be installed in all the coastal districts along the coast of Tamil Nadu so that we can get evenly distributed data to establish a pattern.
Which coastal communities in Chennai would suffer most from sea level rise?
Low-level areas such as Ennore, surrounding areas of Adyar and Cooum will be submerged in 15 years. Since land level is almost equal to the sea level at Ennore, even a slight rise in the latter is bad. Considering the fact that Ennore has turned into an industrial hub with thermal power and petrochemical industries, the SLR is alarming.
What is the status of mangroves in Chennai?
In Chennai, Ennore is an ecological hotspot with significant mangrove population. There are about 20 patches of mangroves in Ennore, with each patch covering about three to five hectares. But ongoing developmental activities are affecting the mangroves at Ennore. The Adyar mouth region near Theosophical Society also has mangroves. Concrete bunds have destroyed mangroves alongside Cooum River.
Is there scope of replanting mangroves along the sea coast of Chennai. If yes, where and how?
Mangroves grow in muddy areas and not on sandy beaches. They can be grown only in Ennore and in the muddy areas of Cooum and Adyar. Adyar Poonga did a good job of planting mangroves. Mangroves help in the growth of the fish population. In one hectare of mangrove-rich coast, we can expect at least 600 kilos of fish and 100 kilos of prawn in a year. The only setback is time. If you plant them today, you will reap the benefits only after 12 years.
Is the Coastal Regulatory Zone 2011 notification being implemented satisfactorily in Chennai?
Implementation of CRZ 2011 is important, as a solution to climate change. In general, the implementation of CRZ in rural coastal areas has been satisfactory. But it is not up to the mark in Chennai. The unregulated growth of resorts in the coastal hot zones should be checked. However, the release of coastal zone regulation maps is a relief, as it gives an opportunity for the the environment-conscious to monitor and check encroachments, and take steps to have them rectified.
What is the most urgent measure necessary for Chennai Coast at this moment?
Chennai coast should have seawater quality monitoring to check the heavy metal pollution, biological oxygen demand and faecal coliform bacteria. But unfortunately, there is no awareness of the subject. Knowledge of seawater quality is important for the public, so that they can avoid swimming in the polluted waters.
** The designation of the interviewee was corrected post publication