Context

The city witnessed its third wettest day of October in the last 10 years and was listed as the rainiest place in the country by Skymet, an independent weather forecasting agency, after it recorded 72.5mm of rainfall.

About

Geographic details of the city

• Hyderabad, the capital of the southern state Andhra Pradesh is located on the banks of Musi River in Deccan plateau.
• The city boasts of a unique landscape of rock formations that are almost 2.500 years old.
• The city has red sandy type of soil and falls in the seismic zone-I which makes the land least exposed to earthquakes.
• The highest point in Hyderabad is Banjara Hills and the contour level gradually falls from west to east which leads to the creation of a trough near the Musi River that runs through the city.
  • This feature has facilitated sufficient water supply to the city.
• Hyderabad is endowed with a system of catchments.
  • Its western edges are in the Godavari river basin (from Kukatpalli, Ramachandrapuram to Gachibowli)
  • Its eastern part is in the Krishnaa river basin
• The Deccan region as a whole has a chaotic drainage pattern – water does not flow in a single direction, as the slope moves in multiple directions.

Reasons behind the heavy rainfall

• There are occasions when winds are carrying huge amounts of moisture from the Arabian Sea and dumping all across Central India, including Maharashtra, Telangana, parts of Odisha and up to Assam, triggering such events.
• Temperatures are rising everywhere and in warm conditions, the air can hold more moisture for a longer period of time.
• Then there is the issue of land use patterns, which is dominated by concrete these days. When air holds a lot of moisture, then the rains are heavy.

IMD Data As per India Meteorological Department (IMD) data, Hyderabad witnessed 98.3mm rainfall on October 10, 2013 and 82.6mm on October 3, 2017. The IMD data indicates that the city has been pounded with 356mm of rains in 18 days, which is four times higher than the normal rains. The city received 18 days’ worth rainfall in just one day.

What’s exaggerating the situation?

• Overflow of lakes: Much of the damage was due to the overflowing of lakes — in particular, the Hussain Sagar Lake and the breaching of storm water drains.
• Construction: Construction over lake beds and encroachments of drainage channels have been identified as problems that have exacerbated flooding and inundation in the city in the past (the deluge in August 2000, for example).
• Lost wetlands: Wetlands and watersheds play a vital role in absorbing excess rainfall, but regrettably, rapid urbanisation has resulted in the loss of a large portion of the wetlands.
  • An analysis by the Centre for Science and Environment in 2016 revealed that 3,245 hectares of water bodies were lost in Hyderabad between 1989 and 2001.

Mokshagundam Viseswarayya recommendations The last time the city saw serious flooding was in August 2000, with rainfall of 24 cm in a single day, claiming 15 lives. In 1908, the River Musi was in deluge, subjecting leading to as many as 15,000 deaths. This calamity prompted the government to rope in veteran irrigation expert Mokshagundam Viseswarayya for a study on flood mitigation. Osman Sagar and Himayat Sagar were built to act as flood control centres as a result of the expert’s recommendations. But one of his vital recommendations – a modern drainage system – still remains a dream.

What needs to be done?

• Hyderabad urgently needs to expand and remodel its drainage system.
• In the long term, the effects of flooding due to deluges can only be mitigated if urban planners take into account the hydro-geology of cities and ensure that construction, development and land occupation do not take place in a way that reduces the area of wetlands.