Chennai warmer temperature study by the Center for Water Resources


Shrinking water bodies and green cover in Metropolitan Chennai lead to increase in land surface temperature

Shrinking water bodies and green cover in Metropolitan Chennai lead to increase in land surface temperature

The Chennai metropolitan area, predominantly agricultural in 1988, has nearly 48.7% built-up area. Decadal changes in land use and urban sprawl have led to warmer temperature and an increase in the urban heat island effect spreading to the peri-urban landscape.

This was one of the key findings of a study titled “Monitoring Spatio-temporal Dynamics of Urban and Peri-urban Land Transitions – A Case Study of Metropolitan Chennai” by the Water Resources Center of the Anna University.

According to the survey which covered an area of ​​1,189 km2 including parts of Kancheepuram and Tiruvallur districts, the CMA had a vegetation cover of nearly 17,770 hectares or 14.9% of the area in 1988. It decreased considerably to 7,288 hectares, which represented only 6.1% of the area in 2017.

Similarly, bodies of water, which occupied nearly 8,023 hectares, or 6.7% of the area in 1988, decreased by 5,569 hectares, or 4.6% of the CMA.

While the extent of agricultural land had decreased from 42.2% in 1988 to 19.2% in 2017, it was replaced by urban built-up area. Rapid urbanization, particularly along East Coast Road and Rajiv Gandhi Salai and GST Road, has led to an increase in built-up area to 48.7% in 2017 from just 17.7% in 1988. Urban settlements are denser, from just 21,122 hectares in 1988 to 57,839 hectares now, according to the study.

Heat island effect

As peri-urban areas develop with denser urban sprawl, especially over the past three decades, they experience warmer temperature due to the urban heat island effect, Mr. Krishnaveni, professor (water resources) and director of the Institute for Ocean Management, who co-authored the study.

The loss of water bodies, wetlands and greenery that have been replaced by built-up areas has increased the land surface temperature (LST) since 1988. This is the radiative temperature of the earth’s surface or earth temperature after solar radiation as measured by remote sensor.

For example, the extent of peri-urban areas that experienced an LST of 31 degrees Celsius to 34 degrees Celsius increased from 29.77% in 1988 to almost 68.18% in 2017. The impact of urban sprawl is is also being felt on the city’s outskirts with diminishing tree cover, agricultural land and shrinking water bodies. While space experiencing LSTs above 34 degrees Celsius was just 0.01% in 1988, it has now risen to 3.21%, said Mr Mathan of the Center for Climate Change and Stewardship. disasters and author of the study.

Spectral indices from remote sensing and GIS technologies were used to assess land use dynamics over decades. More areas of the city are now experiencing warmer temperatures due to the urban heat island effect, he said.

Efforts should be made to increase green cover and protect wetlands in peri-urban areas to maintain LST below 30 degrees Celsius. Creating an inventory of water bodies and environmentally sensitive areas would help reduce construction activities and reduce the negative impact of urbanization, Ms Krishnaveni said.

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