Long monsoon? Why is it raining in Bengaluru?

Bengaluru, Sep 06: Heavy rains in the past two days battered parts of Bengaluru, particularly information technology corridor and arterial roads, with several localities inundated, there by affecting normal life.

The situation in several parts of the IT capital city including Yemalur, Rainbow Drive layout, Sunny Brooks Layout, Marathahalli continued to remain the same today with waterlogged roads, houses and vehicles partially submerged. Cars were seen floating in waterlogged Basvanagar and luxury villas were completely flooded with rescue ops underway.

The southern districts of Karnataka have witnessed a wet season since June. Bengaluru city observatory recorded the wettest South West monsoon in history by receiving a massive 953.4 mm of rainfall since June 1st. The previous record of 949.7 mm was recorded in 2017. The top 2 of the wettest SWM seasons in recorded history have occurred in the last 5 years.

Karnataka Chief Minister Basavaraj Bommai said that the entire Bengaluru city has not been affected by flooding and that the problems are concentrated in two zones, particularly in the Mahadevapura and Bommanahalli area.

So, why is it raining so heavily in Karnataka?

The formation of low-pressure area over west central Bay of Bengal in the subsequent two days tends to be a common occurrence during the southwest monsoon season.

As per the India Meteorological Department (IMD), under its influence heavy rainfall are also likely Coastal Karnataka, North Interior Karnataka and South Interior Karnataka including Bengaluru during the next few days.

While it persists, this low-pressure will interact with other meteorological parties such as the east-west shear zone across North Peninsular India and the active monsoon trough that lies south of its normal position. Subsequently, their combination will result in the continuation of heavy rainfall across East, Northeast, Central and West India during the course of this week.

However, the garden city received the excess rain was mainly due to a shear zone that had developed nearly 4.5-5.8 kilometers above mean sea level that deposited heavy rains in south interior Karnataka, including Bengaluru City.

Dr Geeta Agnihotri, head of the Regional Meteorological Centre, Bengaluru, told indiatoday.in that the very heavy rains in Bengaluru city were due to the shear zone that had formed. "It's a normal occurrence during monsoons just as the formation of troughs, circulations, and low-pressure regions that drive monsoonal rains," she said.

A shear zone is a monsoon weather feature that is an area filled with opposing winds concentrating heavy rain in that zone, the report says.

The position of the monsoon trough is favouring rainfall in Karnataka and Kerala. It is a low-pressure area, which is a semi-permanent feature of the circulation of monsoon. When the trough migrates southward, it results in a heavy monsoon.

In contrast, the northward migration of this trough leads to a break in monsoon conditions over a major part of India and heavy rains along the foothills of the Himalayas and sometimes floods in the Brahmaputra river, according to IMD.

On August 25, the weather office had predicted an early withdrawal of southwest monsoon against the normal date of September 17. India has received six per cent excess rainfall this monsoon but large parts of Uttar Pradesh, Bihar, Jharkhand, Manipur, Tripura and West Bengal have reported deficient rains, which has affected the rice crop this kharif season.