Maharashtra, West Bengal, Bihar and Assam faced severe rain fury during monsoon season this year, displacing normal lives of lakhs of people. A new study by Indian scientists has recorded a three-fold rise in such erratic rainfall over central India — from Gujarat in the west up to Assam in the northeast — and suggested that such rainfall is going to be far more frequent in the upcoming years and decades.
Scientists have attributed it mainly to the rapid warming of the Arabian Sea. According to the study, with the passing of each decade, 13 more incidents like these are noticed, thus making floods an annual affair for people living in Gujarat, Maharashtra, Jharkhand, Chhattisgarh, Madhya Pradesh, Bihar, West Bengal and Assam.
As part of this joint study, researchers, led by Roxy Mathew Koll from city-based Indian Institute of Tropical Meteorology (IITM), along with experts from IIT-Bombay and University of Maryland, have tracked this rising trend during 1950-2015 period, where widespread extreme heavy rainfall (150 mm or more) was observed over a span of over 5 lakh square kilometre area along central India.
Statistics from the International Disaster Database show that close to 70,000 people lost their lives and another eight crore people were rendered homeless in the 268 events of heavy rains, flash floods, torrential rains or landslides recorded over central India in the last six decades. The sea warming has been noted along the north of the Arabian Sea — the Indo-Pak region and along regions in the northwest closer to the gulf. “Due to excess warming, there is significant amount of moisture available in the atmosphere. This moisture then gets transported by strong surges of westerly winds over to the Indian mainland during the monsoon, resulting in widespread and heavy rainfall over central India,” said Koll.
Human activities after industrialisation have triggered an exponential rise in the green house gas emissions and pollutants. In addition, frequency of events like El Nino, the abnormal warming of central and east-central Pacific Ocean have been proved to be the driving forces for the warming of Arabia Sea during the recent decades.
Incidentally, the number of cyclones originating from the Arabian Sea has increased. “Its impact on India has been mainly the change brought in the rainfall duration and amounts. On one hand, coastal and peninsular India has experienced rainfall deficits and for the last three consecutive years, some parts of Karnataka and Maharashtra have remained dry. On the other hand, northwest is getting flooded far too often and this trend is seen extending to the Northeast. All this simply indicates that the pre-monsoon heat and humidity have increased and it has the most severe impact on farmers, preparing their land for the monsoon season,” Raghu Murtugudde, senior researcher from University of Maryland, told The Indian Express in an email interview.
Unlike what was believed earlier – that it is only the depressions formed in the Bay of Bengal which are responsible for most heavy rains during June to September over India – this study has painted an altogether different picture. Researchers at IIT found that the Arabian Sea holds as high as 36 per cent moisture, followed by land evaporation contributing up to 29 per cent and, lastly, moisture pumped-in by the Bay of Bengal contributes is the lowest at 26 per. “Our findings indicate that land transpiration is also a major contributor to the Southwest monsoon and there is a need to consider it during the operational forecasts,” said Subimal Ghosh, researcher at IIT-Bombay.
Unlike the Pacific or Atlantic Oceans, which vent out their excess heat over to either of the poles, researchers categorically highlight that the Arabian Sea has no such option available. “Since the warmer areas over the Arabian Sea have also been noted to be landlocked region, the sea here has little or no avenues to release its latent heat into the atmosphere,” said Koll.
However, weather experts also suggest that since such extreme events do not occur in a short span of time, forecasters have a bigger role to play. “Short-term forecasts are getting better and will continue to do so in the coming years. So, we can have better planning and management for protecting crops, for which solutions like agro-forestry, where trees would shelter crops and reduce the water runoff and prevent soil erosion,” Murtugudde said.
In addition, experts feel that the local administration in urban areas like Mumbai, Chennai and Bengaluru, which have, in recent years, experienced severe flooding caused due to extremely heavy rainfall over a short span of time, can make better use of these forecasts and improve management of transportation, schools, hospitals and storm drainage in such situations.