Frequent extreme rain behind rising incidents of floods in 2016
Nearly 150 events of extremely heavy rainfall of more than 200mm each, occurred during this year’s southwest monsoon between June and September, indicating the high frequency of such events, a post-monsoon report of India Meteorological Department (IMD) revealed. These extremely heavy rainfall events triggered large-scale flooding and flash floods across the country, killing hundreds across the country.
India Meteorological Department’s (IMD) categorizes rainfall between 64.5mm and 124.4mm as heavy rain while rainfall between 124.5 mm and 244.4mm is categorized as very heavy rainfall. The extreme rainfall events were concentrated in Arunachal Pradesh, Assam, West Bengal, Madhya Pradesh, parts of Rajasthan, Konkan region and western Maharashtra.
The trend of these events occurring in shorter durations is becoming more frequent and intense, leading to incidents such as the Mahad bridge collapse. In August this year, a colonial era bridge on the Mumbai-Goa bridge national highway collapsed as strong currents in Savitri river flowing beneath it shook its foundations and plunged two transport buses and private vehicles in it, killing over 20.
This incident was triggered following intense downpour upstream in Mahabaleshwar, where Savitri river originates. In fact, the data that has come from IMD’s report shows that there were five extremely heavy rain events in the hill-town of Mahabaleshwar between July 29 and August 6.
Meteorologists and weather scientists said that many recent studies have indicated that there has been a rise in heavy and extreme rain events in India and even globally. Anthropogenic climate change has been cited as one of the chief reasons behind this rising trend. “With rising temperatures, the water bearing capacity of atmosphere increases and more moisture is drawn from the oceans. The result is sudden precipitation and this phenomenon has been documented globally,” said KJ Ramesh, director-general, IMD.
According to IMD’s analysis of rainfall data between 2009 and 2013, Odisha, Konkan, Goa, Coastal Karnataka, Assam, Meghalaya, Arunachal Pradesh, Kerala have all witnessed heavy rainfall days for more than 20 days during the monsoon season. Odisha, Konkan, Coastal Karnataka Sikkim, Assam and Meghalaya recorded an average of 70 heavy rainfall events in that period.
“The seasonal monsoon data has also shown that the number of light to moderate rainfall days is declining since 1980’s, compared to the years before that,” added Ramesh.
In its report, the IMD has also reflected on its monsoon forecast, that was off-mark. The IMD had predicted that the monsoon will be 106% or above-normal in the June-September period, but the actual monsoon turned out to be 97% or normal. “Prior to June, most of the climate forecasting models were indicating high probability for the development of La Niña during the second half of the monsoon season, which was supposed to favour normal to above normal rainfall over India.However, that did not happen,” the report said. The opposite of El Nino weather phenomenon wherein warmer than usual Pacific waters trigger droughts in South Asia, La Niña usually brings heavy rainfall in South Asia.
The report added that with La Niña not developing against the expectation of global El Niño/ La Niña forecast and below normal rainfall during June and August, due to unfavorable phases of intra-seasonal activity, caused the most of the operational forecasts to overestimate to the actual rainfalls.