While flood waters receded in some parts of Bengaluru on Wednesday, the worst is not over for IT capital yet, with the weather bureau predicting heavy rainfall over south interior Karnataka, including the city, for the next two days.
Heavy to very heavy rainfall is predicted over a few places in coastal and south interior Karnataka on September 8-9 and interior Karnataka on September 9-10, according to the India Meteorological Department (IMD).
"A cyclonic circulation lies over interior Karnataka and neighbourhood. A trough runs from cyclonic circulation over east-central and adjoining southeast Bay of Bengal to north Kerala across Rayalaseema and south interior Karnataka," it said.
While experts have attributed the flooding in IT capital to encroachments on the stormwater drain and water bodies which impede the flow of rainwater, excess rain has also played its part.
According to IMD data, the Bengaluru City observatory recorded 251.4 mm of rainfall in the last four days, including 131.6 mm on Sunday, the highest 24-hour precipitation in September in 34 years.
Before this, the observatory gauged 132.6 mm on September 26, 2014. The all-time high is 177.6 mm recorded on September 12, 1988, senior IMD scientist R K Jenamani said.
The Bengaluru HAL Airport Observatory recorded 271.2 mm of rainfall during this period, including 123.8 mm on Sunday.
The Bengaluru KIAL Observatory reported 158 mm of precipitation in the last four days, including 109.6 on Sunday.
"This is not a localised phenomenon. We have seen large excess rainfall over Tamil Nadu, Lakshadweep, north interior Karnataka, south interior Karnataka in the last one week," Jenamani said.
On September 3-4, a convergence line extended from Comorin area to north interior Karnataka at lower level.
A convergence line is a band of cloud that remains fairly stationary and can produce large amounts of rain across a relatively small area.
Thereafter, a cyclonic circulation formed over south interior Karnataka. It lay near Bengaluru on September 4 night.
A local Met official said a shear zone deposited heavy rains in south interior Karnataka including Bengaluru city on Sunday.
A shear zone is an area filled with opposing winds concentrating heavy rain in that zone.
According to the IMD data, Bengaluru Rural gauged 752.3 mm of rainfall against a normal of 303.5 mm between September 1 and September 7 -- an excess of 148 per cent.
Bengaluru Urban received 168 percent surplus rainfall -- 840.2 mm of precipitation against a normal of 313.2 mm -- during the period.
In August, Bengaluru received 370 mm of rainfall, a little short of the all-time record of 387.1 mm of rainfall in August 1998.