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Hyderabad’s heavy rainfall trends reason why urbanisation needs to be studied in context of climate change

Dr Y V Rama Rao, former Deputy Director-General of IMD, does not think it is only the changing rainfall pattern that has wreaked havoc time and again, but the inability of the urban infrastructure to deal with the rains.

Written by Rahul V Pisharody | Hyderabad |
Updated: October 26, 2021 12:34:39 pm
Vehicles drive through a waterlogged area in Hyderabad. (PTI Photo)

Hyderabad was in the grip of fear after two consecutive days of heavy rains threw life out of gear on October 8 and 9. It was an eerie reminder of the deluge of October 2020 when the worst downpour in nearly a century resulted in urban flooding.

For three years in a row since 2019, Telangana, once known for its semi-arid climate, has recorded an excess of rainfall during the southwest monsoon. A change in the rainfall pattern is being witnessed in the state and its ever-expanding urban agglomeration Hyderabad. As much as it is visible, a recently released state government publication has, in one of its conclusions, noted an increase in rainfall in southern Telangana districts, including Hyderabad, as compared to northern and eastern districts, which show a declining trend in annual rainfall.

Telangana rainfall intensity during the southwest monsoon season.

The analysis published in the latest edition of ‘Weather and Climatology of Telangana’ studied district annual rainfall data over the last 30 years. The declining trend is about 110 mm to 157 mm for districts of Nirmal, Mancherial, Kamareddy, Sircilla, and Suryapet. On the other hand, districts such as Hyderabad, Warangal Urban, Bhadradri Kothagudem, Jogulamba Gadwal, Wanaparthy, Mulugu, and Narayanpet are showcasing an increase of 25 mm to 75 mm in annual rainfall.

This is even as the eastern Telangana districts continue to receive an increased number of wet spells and also more events of heavy and very heavy rainfall days. A wet spell is a period when a minimum of 2.5 mm rainfall is recorded in a day and a cumulative rainfall of 100 mm is recorded in five or more days. Incidentally, 162 of the total 432 such wet spells between 2004 and 2020 were recorded during the last five years. Though the southern districts have been recording an increase in annual rainfall, the number of wet spells was on a decline between 2004 and 2020.

Year-wise heavy and very heavy rainfall events during the southwest monsoon season from 2004 to 2020.

The number of automatic weather stations recording heavy rainfall (64.5-115.5mm) and very heavy rainfall (115.6 mm or more), too, have been on a decline in southern districts. This is despite the state witnessing a rising trend in the number of heavy and very heavy rainfall days in the last 17 years.

Dr Y V Rama Rao, former Deputy Director-General of India Meteorological Department (IMD), pointed out the increased frequency of extreme rainfall events supported by increasing temperatures and humidity for these changes. According to him, the south-eastern belt of Greater Hyderabad, which includes Hayathnagar, LB Nagar, Uppal, Saroornagar, Malkajgiri, Kapra, etc, are turning more prone to extreme rainfall events in recent years. “We are witnessing dumps of rainfall in short spells here when other areas of GHMC are receiving normal rainfall. Climate Change is certainly one of the factors causing high impact changes in weather, but in this case, we need more micro-level analysis,” said Rao, the author of the publication and a consultant with the Telangana State Planning Development Society.

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The deluge of October 13 and 14, 2020, in Hyderabad was one of the worst-ever extreme rainfall days in a century. In just 24 hours, localities such as Ghatkesar and Hayathnagar on the outskirts of Hyderabad had recorded 32.4 cm and 30 cm of rainfall, respectively.

Scenes of overflowing lakes, inundated roads, and floating vehicles have started becoming common as short intense spells of over 40 mm rainfall have become frequent. Dr Rao does not think it is only the changing rainfall pattern that has wreaked havoc time and again in Hyderabad, but the inability of the urban infrastructure to deal with the rains.

Dr N V Umamahesh, professor of Civil Engineering at National Institute of Technology-Warangal, feels rapid urbanisation and changes in land use have caused water bodies to shrink and nalas to be encroached upon while existing stormwater drains have become inadequate to carry more frequent rains of higher intensity.

Increasing the size of stormwater drains, he said, is not the solution, but instead, the government should look at developing technology to forecast the flows and control flooding in case of an extreme rainfall event to minimize the damage. Also, as the city continues to expand, it could be mandated that newer colonies and gated communities should have water infiltration trenches and mechanisms for water recycling. “By fully recycling water, we will be able to better manage our water supply and also reduce the stress on stormwater drains,” Dr Umamahesh said.

A waterlogged street after heavy rain in Hyderabad. (PTI Photo)

As part of a project from the Ministry of Electronics and Communication, experts from IISc Bangalore, NIT Warangal, BITS Hyderabad, and CDAC Trivandrum have been working on exploring technology to minimise the damage during urban floods. “One aspect is to be able to forecast extreme rainfall events two or three hours in advance. Secondly, real-time monitoring of rising water levels or waterclogging at different places using sensors on the ground. The project could not take off in GHMC,” Dr Umamahesh added.

Dr Umamahesh said researchers have developed hydrologic and hydraulic models that could locate areas that could get inundated. “In terms of risk, we tried to understand areas that are prone to flooding, depth of inundation, the velocity of flow, classify different zones, etc. You need data from the ground to calibrate these models and make them precise.” Based on the real-time forecast of rainfall and monitoring water levels, residents of respective localities could be alerted or even be evacuated in time. “You cannot undo the damage done to the city. It is not possible to prevent frequent urban floods now. The best you can do is prepare the response,” he said.

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In November 2020, the state government announced the setting up of an exclusive project wing in the Greater Hyderabad Municipal Corporation (GHMC) to mitigate future flash floods in the city. The Strategic Nala Development Programme (SNDP) was mandated to study the existing stormwater drainage system across the city and identify critical narrow points, encroachments on its path, and related issues, before submitting reports to begin work in a mission mode.

Nearly a year after its announcement, no work is visible on the ground. When contacted, C Vasantha, the officer on special duty heading SNDP, said the tenders for the work identified are being floated, and awarding of contracts is in progress. Without divulging details, she said work on SNDP will begin next month.

As of date, authorities have identified 52 specific projects across six zones of GHMC and also in the adjoining municipalities worth Rs 858 crore. Of the total, 33 projects are in Greater Hyderabad, and LB Nagar zone tops the list with 10. Presently, 12 projects are under evaluation, tenders have been floated for eight and are being called for seven. Besides, Detailed Project Reports (DPR) for six projects are yet to be submitted by consultants, said sources. For all the 19 projects in adjoining municipalities of Hyderabad Urban Agglomeration (HUA), DPRs are yet to be received by SNDP.

A car is submerged after rains in Hyderabad.

Some of the work includes remodeling or widening of existing nalas, desilting, restoration of lakes, construction of new bridges and sluice gates, and allowing for diversion of runoff from water bodies to nearby colonies. According to SNDP, the problem of inundation of low-lying areas can be controlled to up to 50 per cent by taking up work on nearly 78 km of total 473 km in the first phase, covering 45 per cent of the drainage network within HUA. The rest of the projects are scheduled in phase-2.

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Senior hydrogeologist BV Subba Rao, who has been studying the region for over three decades, said a ‘nala strategy’ which is not in tune with academic research work will do no good in preparing for a flood-resilient city. “We must first study the stormwater trend with the natural systems because the North East and North Hyderabad (Nacharam, Mallapur) have a different drainage pattern than the West. It is ministers and engineers who are talking about a nala strategy, but there is no synergy between applied academic research and implementation of the strategy.”

Rao, like many other weather experts, spoke of two things that happened. One, an increase in the frequency of isolated heavy downpours in city pockets, and two, a rise in temperatures between spells of rainfall during the monsoon. Such heavy spells of rainfall till a few years ago was common in Jubilee Hills and Madhapur, but now is mostly seen around LB Nagar, Saroornagar, etc, he said.

“Our focus is on studying action in the sky while the impact is on the ground. But the action starts because of the heat radiation from the ground that is caused by erratic urban development. The need of the hour is a comprehensive study on the city’s growth, heat radiation, and its relation with cloud bursts.”

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