Monsoon is officially over but likely to withdraw only after Oct 10: IMD
The monsoon which recorded “above normal” rain at 110% of long period average (LPA), is expected to begin its withdrawal by October 10.
The southwest monsoon which triggered heavy rain across many parts of the country officially came to an end on Monday with “above normal” rain at 110% of long period average (LPA), the India Meteorological Department (IMD) said on Monday.
But the monsoon’s withdrawal is likely to begin only around October 10 - the most delayed withdrawal since 1961 (October 1) and 2007 (September 30). The tail end of the monsoon has left a trail of heavy rain and flood in Bihar and Uttar Pradesh.
In spite of late onset of the monsoon on June 8 and that month ending with a deficiency of 33%, July, August and September received 105%, 115% and 152% of their LPA respectively. IMD had predicted a near normal monsoon at 96% of LPA in May. The prolonged monsoon season was not forecast by IMD.
“IMD had predicted that the monsoon performance would be better in the second half compared to the first half. IMD’s analysis on weakening of El Nino and development of a positive Indian Ocean Dipole (IOD) and the second half monsoon rainfall being above normal were thus proved correct. However, quantitatively, realised rainfall during the second half was more than what IMD predicted,” the met department said in a statement.
“We will not consider the rainfall received after this to be monsoon rainfall. It will be counted as post monsoon season rainfall. IMD considers June, July, August and September as monsoon season,” said M Mohapatra, director general, IMD.
Climate scientists said IMD has not updated its withdrawal dates for decades. For the last ten years monsoon has been beginning its retreat after September 20. Mohapatra added “Northeast monsoon (winter rains in peninsular India) usually arrives in October. We don’t have any update on northeast monsoon yet.”
Out of 36 meteorological subdivisions, two sub divisions received “large excess” (60% over LPA), 10 received excess (20% to 59% over LPA) and 19 sub divisions received normal monsoon (-19% to 19% over LPA ) rainfall, 5 sub divisions however received deficient rainfall. In Haryana, Delhi and Chandigarh deficiency was 42%. “On an average, about 20% of area of the country receives deficient or scanty rainfall during the monsoon season,” the statement said.
The defining features of this monsoon were the high number of extreme rain events. For example, there were 1269 weather stations reporting very heavy and extremely heavy rain in August out of which 282 were extremely heavy rainfall events, highest in the past five years. The data on extreme events is yet to be compiled by IMD, Pune.
IMD officials said delayed monsoon withdrawal is a feature of climate variability. “Monsoon withdrawal always begins from the northwest part of the country. The first and foremost condition to announce monsoon withdrawal is rainfall should stop completely for about five days, there should be significant reduction in moisture and anticyclone flow should be established. None of this has happened yet,” said K Sathi Devi, Head of the National Weather Forecasting Centre.
“June to September is the normal monsoon season but variability can happen. We need to see long tern data to conclude whether this is a result of climate change. Extreme rain events, however, can be definitely linked to climate change. There is a rise in extreme rain events in recent years. In August this year there were more than 1,000 extreme rain events,” said Pulak Guhathakurta, head, Climate
Application and User Interface, Climate Research and Services at IMD Pune. But, projections made by a team of scientists at Indian Institute of Tropical Meteorology (IITM) Pune based on various models shows intensification of the southwest monsoon and increase in mean monsoon rainfall by mid century.
“A series of low-pressure systems from the Bay of Bengal are responsible for the monsoon’s delayed withdrawal from western Rajasthan this year. Conditions had become favourable for the monsoon’s withdrawal from western Rajasthan around September 18. However, a low-pressure circulation (which seeded Tropical Cyclone Hikka in the Arabian Sea) changed the wind pattern over the state and caused a further delay in the monsoon’s withdrawal,” said Akshay Deoras, Ph.D researcher, department of meteorology, University of Reading, UK.