Extreme rainfall marked 2019 monsoon, says IMD
Last year also saw the highest proportion of districts, 77%, in at least 13 years register excess or normal rainfall, according to the India Meteorological Department’s 2019 monsoon report released on Wednesday.Updated: Jan 17, 2020 00:23 IST
In 2019, 21 of the country’s 559 meteorological stations registered new 24-hour rainfall records compared to 12 stations in 2018, 16 in 2017, 12, again, in 2016 and 18 in 2015.
Last year also saw the highest proportion of districts, 77%, in at least 13 years register excess or normal rainfall, according to the India Meteorological Department’s 2019 monsoon report released on Wednesday.
“The season had several record-breaking extreme rainfall and resultant flood events that caused human casualty and damage to property in Maharashtra, Karnataka, Kerala, West Bengal, Odisha, Uttar Pradesh and Madhya Pradesh,” the report said.
Some weather stations that registered new rainfall records were Kodaikanal, Vadodara, Coorg, Ooty, Alibaug, and Belgaum.
The detailed monsoon report , which captures the extremities of last year’s monsoon and meteorological factors which led to floods in Mumbai, Kerala and Bihar was released at IMD’s 145th foundation day celebration on Wednesday.
IMD’s analysis of the 2019 Kerala floods revealed that the conditions leading to extremely heavy rainfall were very similar to those of 2018 and that the Western Ghats made the state vulnerable to such unprecedented rainfall. Kerala received rainfall that was 123% above normal in August , and above 187% and between August 1 and 15.
The report stated that the extremely heavy rainfall spell in the state could be attributed to the formation of a depression over the northwest Bay of Bengal on August 6. This system intensified and moved northwest on August 7 and 9 which led to the strengthening of westerly and south-westerly winds along the Kerala coast as the cross equatorial monsoon flow increased.
“This essentially means that the monsoon winds were running perpendicular to the Western Ghats which acts as an obstruction. This leads to thickening of clouds and severe rainfall. This was seen in 2018 too. But in 2018 there was enhanced rainfall from June which also led to filling up of reservoirs in Kerala,” explained Sunitha Devi, senior IMD scientist who co-edited the report. The 2018 floods in Kerala resulted in over 400 deaths and caused untold destruction in the state.
Among other extreme weather events of last year’s monsoon, IMD lists extremely heavy rainfall seen over Mumbai on 1-2 July and flooding over south Maharashtra in August. On July 2, northeastern parts of Mumbai received f 30 to 40 cm rain in 24 hours with Santacruz alone recording 37.5 cm rain compared to a normal of 3.71 cm. But Colaba hardly reported any rainfall during that period indicating that the event was extremely localised. “A similar event was seen on July 26 during the 2005 Mumbai floods when Santacruz received 94 cm of rainfall in 24 hours but Colaba recorded only 7 cm. Such localised phenomenon is being studied,” said Sunitha Devi.
During the first week of August, Satara, Sangli, and Kolhapur in Maharashtra received “large excess” rainfall with a departure of 431%, 406% and 344% above normal respectively. The severe flooding was attributed to three parameters—movement of monsoon depression over central India, an offshore trough (area of low pressure) along the west coast and presence of a shear zone. The report also highlighted extremely heavy rainfall spells over Madhya Pradesh, Vidarbha and Chhattisgarh in central India.
“Our study based on IMD data has shown there is a threefold rise in extreme rain events over Western Ghats and Central India. For example, the number of extreme rainfall events over Marathwada increased almost three-fold between 1950 and 2018 from about three extreme rain events (1950s) to about 8 (post-2000) in monsoon months,” said Roxy Mathew Koll, climate scientist at Indian Institute of Tropical Meteorology, Pune.
“2019 was a year of extremes. There was severe heat wave in Bihar, excess and prolonged monsoon; there was some serious cyclonic activity in the post monsoon season, between December 15 and 31 there was a severe cold spell,” IMD’s director general, M Mohapatra said on Wednesday.