Hyderabad: An unusual phenomenon in October, of low pressure systems that kept forming continuously over the Bay of Bengal and moving into Telangana, has caused the ‘very huge rainfall’ in the State capital, leading to the floods in different areas of the city.
According to officials from the India Meteorological Department, Hyderabad, it was a deep depression over the Bay of Bengal on October 13, which moved inward into Telangana on October 14 as a depression that caused the heavy rains measuring 191.8 mm, a 117-year-old high and in turn triggering the floods. However, instead of the usual process of withdrawal of such low pressure systems by October 15, more were forming, which were behind the continuing rains over Telangana.
“There are lots of low pressure systems over the Bay of Bengal and moving into Telangana now, which in October is unusual. By this time or mid-October, the withdrawal should have set in. But instead, we are seeing record amount of rainfall incessantly that should allow for the withdrawal to begin,” said K Nagaratna, Head, IMD-Hyderabad.
IMD India has already issued a report saying that the monsoon too, which should have withdrawn by October, was unlikely to leave any soon due to the intense low pressure systems that were forming, in the Arabian Sea and the Bay of Bengal too, which meant apart from the Southwest coast, the Eastern coast of the country and States alongside it could be the next venues for such rainfall.
As for these depressions concentrating over urban areas like Hyderabad, weather officials say the reasons could by myriad, ranging from the now well chronicled global warming impact to what is known as Urban Heat Island Effect as well. The heat island effect was causing floods in several urban areas across the world, according to various reports, they said, adding that construction and similar human activities more in cities, and therefore triggering such floods more in urban than rural areas.
The threat of urban flooding
From Chennai, Tamil Nadu in 2015 to Kerala, Maharashtra and Karnataka in August 2019, and again Mumbai recently, urban floods are increasingly becoming a major concern in the country, with Hyderabad being the latest example of the phenomenon.
This, in fact, is not an issue restricted to Hyderabad or India, with several countries facing the same threat. Municipal Administration and Urban Development Minister KT Rama Rao had on Monday pointed out that even global cities were facing the threat of urban flooding with such rainfall recording beyond their handling capacities.
According to a report, ‘The Growing Threat of Urban Flooding: A National Challenge’, done by the University of Maryland and the Texas A&M University in 2018, several cities across the United States were facing the issue.
In January 2018, heavy rains unleashed destructive rivers of mud and debris in Southern California leaving at least 13 people dead while urban flooding from 2007 to 2011 in Cook County, Illinois resulted in flood losses of over $660 million dollars. In 2016, the city of Baton Rouge was inundated by an estimated 1,000-year rainfall event that flooded 48,000 structures and created over $1 billion in property damage, the report says.
In June 2006, heavy rainfall over downtown Washington, DC caused major flooding, with several more following in over the last few years in Washington as well as cities including New York, Houston, Maryland, and Dallas.
Stomwater drains can handle only 20 mm rainfall
Various reports from the GHMC over the last couple of years indicate that the city’s 1400-km stormwater drain network was designed to handle only 20 mm rainfall per hour, but was receiving rainfall with an intensity of more than 60mm per hour for the last few years. This year, the intensity went much higher, with more devastating impact.
Among other reasons for the flooding, the civic body found that the natural drainage system was blocked due to high-rise structures while lake encroachments were resulting in poor storage capacity and overflow. There were 530 lakes in GHMC limits, which were now reduced to 169. Indiscriminate dumping of plastic and trash into stormwater drains was another major reason.
To avoid the flooding, remedial measures included clearing nala encroachments, which the GHMC has begun already while the rains in September, had prompted a Rs 300 crore drainage channel capping exercise.
• Shifting utilities like waterlines, sewer lines, electric cables over culvert or below drain-bed
• Alternative holding ponds at low-lying areas
• Rainwater harvesting structures all along roads
• Intercepting and diverting all sewers by laying sewerage network to avoid sewage flow into stormwater drains
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