Agri Business

‘Urban heat island’ phenomenon responsible for heavy rains in short spells

V Rishi Kumar Hyderabad | Updated on October 23, 2020 Published on October 23, 2020

More intense tropical cyclones due to climate change will be common, cautions ADB climate change expert

The growing urban heat island phenomenon in urban areas is responsible for cloud bursts, which bring heavy rains in short spells, as seen in Hyderabad. Such heavy bursts are difficult for urban infrastructure to handle, according to a climate change expert.

Connecting the recent rains in Hyderabad and earlier experiences at Chennai and Mumbai, Dr Ancha Srinivasan, Climate Change Advisor, Asian Development Bank for South-East Asia, said, “This is a La Nina year, which is responsible for capture of more moisture and resultant precipitation as witnessed in Hyderabad recently. The La Nina is responsible for high precipitation in short spells and high rates of moisture retention by clouds, high temperature and heat waves and long periods of drought. This results in warming of the surfaces of seas and oceans and increasing evaporation.”

Destruction of wetlands

Speaking over phone from their Regional Office in Bangkok, Srinivasan said, “Clouds can hold up to 7 per cent more moisture and without wind, this results in heavy downpour. We will see more and more of this phenomenon in urban areas of the country. With more moisture, it becomes too heavy to be blown away.”

Climate change, a crisis on our doorstep

“The cloud burst phenomenon in urban areas is here to stay. More intense tropical cyclones and deep depressions due to climate change will be common. Deep depression is a circulation that carries intense rainfall and has moderate wind speeds less than a cyclone. Warmer air due to global warming carries more moisture than colder air. More moisture translates to more rainfall in cyclonic systems. For each °C rise in temperature the clouds can hold 7 per cent more moisture,” he said.

“There is destruction of wetlands and watersheds. The cumulative loss of natural wetlands is estimated to be 54 to 57 per cent, leading to loss of natural water regulation. Between 1970 and 2014, Mumbai lost 71 per cent of its wetlands, Ahmedabad 57 per cent, Greater Bengaluru 56 per cent, Hyderabad 55 per cent and the NCR 38 per cent,” he said.

Mentioning a report by the Centre for Science and Environment, he said it estimated that Hyderabad has lost 3,245 hectares of wetlands in the last 12 years, all resulting in permanent changes.

On the Covid pandemic and the impact of urban areas and cities in India, he said poor operations and maintenance of urban infrastructure is a result of limited or no budget allocations. India’s cities have lost 25 hectares of wetland for every one sq. km increase of built-up area since 1980.

While there is a growing population, cities are having to face the problem of poor urban hydrological ecosystems and drainage infrastructure — where there is a massive encroachment, unauthorised construction work and dumping of waste in water bodies.

This calls for better land use management codes and standards and checking rural migration to cities. Former President Abdul Kalam’s PURA Initiative — Provision of Urban Amenities in Rural Areas — has to be encouraged. Calling for more investments into Hyderabad Climate Change Service to provide quality data, early warning systems, Srinivasan said, “With an estimated 90 per cent of all reported Covid-19 cases, urban areas have become the epicentre of the pandemic. Coronavirus amplifies climate change impact — like flooding — on vulnerable communities. Therefore, there is a need for multi-agency flood and pollution response and communication system to accommodate Covid-19 management,” he said.

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Published on October 23, 2020
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