Monsoon: Battered North India logs its rainiest 2-wk period in 14 yrs; rain surplus climbs to 37% in 14 days

NEW DELHI: Rain-battered north India just experienced its wettest two-week period in at least the past 14 years, available IMD records since 2012 reveal. From Aug 22 to Sept 4, the region logged nearly 3x of normal rainfall, triggering extreme weather fury in nearly all parts of the region - including cloudbursts on the Vaishno Devi route in J&K, worst-in-decades floods in Punjab, the third highest recorded levels of the Yamuna in Delhi and widespread landslides in Himachal Pradesh and Uttarakhand.

North India recorded 205.3mm of rain in these 14 days against a normal of 73.1mm, accounting for 35% of the region's usual quota for the entire four-month monsoon season. The intense spell has put the region on course to registering its wettest monsoon in 37 years since 1988.

North India, a region meteorologically known as northwest India, has received 691.7mm of rain in the monsoon season (since June 1) so far, nearly 37% higher than normal. Even if the region gets normal rainfall for rest of the season, which ends on Sept 30, the total is likely to cross 750mm. That will put this season's rainfall as second-highest in north India in last 50 years, behind 813.5mm recorded in 1988 and ahead of 737mm logged in 1994.

During the past two weeks of weather fury, the region's total monsoon rainfall surplus climbed steeply from 11.6% on Aug 22 to nearly 37% on Thursday. Across a large region such as north India, the mean daily rainfall to sustain such high levels for two weeks is rare. So, what caused this prolonged spell of intense rain?

"This period saw a rare instance of back-to-back spells of two-system interactions, that is, a 'western disturbance' bringing moist wind flows from regions close to the Mediterranean Sea converging with monsoon winds from the east. The first such interaction took place from Aug 23 to 27, and then another one began on Aug 29 and is expected to last till Friday," said Mrutyunjay Mohapatra, IMD chief.

Such interactions are known to unleash very heavy rainfall and cloudbursts in the western Himalayan states, the most devastating example being Kedarnath deluge in June 2013. While such two-system convergences are uncommon in the peak monsoon period of July-Aug, back-to-back occurrences are extremely rare.

Except for east UP, the two-week spell caused extreme rain in all sub-divisions of northwest India. Punjab was most heavily impacted, logging 388% surplus rain in the first week and 454% in the second. In the past week ending Sept 3, the subdivision of Haryana, Delhi and Chandigarh recorded 325% excess rainfall, Himachal Pradesh 314%, west Rajasthan 285%, J&K 240% and Uttarakhand 190%.