What is causing widespread rainfall across India?

• For the first time this season, the southwest monsoon is active over a large geographical area of India. At least 80% of the country last week reported widespread rainfall, with heavy to very heavy spells lashing Assam, West Bengal, Uttar Pradesh, Uttarakhand, Gujarat, coastal Maharashtra and Karnataka, Kerala, and Lakshadweep.

What factors are causing widespread rains?

• After remaining subdued during mid-June, the southwest monsoon got the much-required impetus towards June-end.
• The monsoon covered the entire country, six days ahead of its normal schedule. Delhi, Punjab, Uttarakhand, Uttar Pradesh, Himachal Pradesh, Rajasthan, and Jammu and Kashmir received the spell in early July.
• However, since the start of this month, there have been multiple favourable weather systems that have kept the monsoon either active or vigorous (with respect to rainfall events) over southern peninsular, east, northeast, and central India regions.
• There have been two main contributors to the enhanced rainfall. One is the continuous incoming of moisture-laden strong westerly winds from the Arabian Sea.
• The other is the position of the monsoon trough — a semi-permanent, low-pressure area extending between Pakistan and the Bay of Bengal during the monsoon season — which usually oscillates between north and south within the season. Whenever it moves towards the south, as it has done in the present case, more rainfall can take place in central, eastern and peninsular India. When it shifts towards the north, the Himalayan foothills are likely to receive more rainfall but the rest of India sees a drop in rainfall.
• Apart from these two factors, other weather systems have also contributed to the widespread rainfall over all regions, except the extreme north India. They are:
• The persistence of an off-shore trough (a shallow trough of low pressure, which develops along India’s coast during the monsoon) between south Gujarat and north Kerala for more than a week now.
• The intermittent development of a wind shear zone — where winds move with different velocities and directions - along latitudes 20° N between central and peninsular India.
• The development of a low pressure system over the west-central Bay of Bengal, off the Odisha coast, on Monday. The system moved over Chhattisgarh and adjoining Vidarbha on Tuesday, and over southeast Madhya Pradesh on Wednesday.

What is the rainfall status?

• The Met department’s rainfall statistics indicate that the all-India rainfall went from 242mm on July 9 to 305.8mm on July 17. The country’s rainfall stands at 97% of the normal for this time of the season.
• Overall, 17 states have either received normal or above-normal rainfall this season. But there are a few states such as Odisha, Haryana, Chandigarh, Himachal Pradesh, and Jharkhand along with high-rainfall recording states including Kerala, Nagaland, Manipur, and Mizoram where the rainfall, this season, has been deficient, so far this season. This is also because July rainfall normal values for many of these states are high.
• Since July 13, some heavy rainfall events have been recorded along the country’s west coast, especially in Konkan, Goa, ghat areas of Madhya Maharashtra, coastal Karnataka, and Kerala. Uttarakhand, west Uttar Pradesh, Gujarat, and West Bengal also received heavy rainfall.

What is the forecast?

• The southwest monsoon will continue to remain active all through this week over south peninsular, eastern India, and over the Himalayan states. A fresh low pressure system will develop over the northwest Bay of Bengal around Friday, whose landward movement will keep the monsoon momentum high with rainfall persisting over eastern and central India regions during the next five days.
• With the monsoon trough most likely to remain to the south of its normal position during the next four to five days, the IMD has issued a ‘red’ alert (meaning : take action) for Kutch, Saurashtra, Konkan, Goa, coastal and south interior Karnataka where very heavy to extremely heavy rainfall (115 mm to 204 mm in 24 hours) is likely to occur on Thursday.
• For July 19, an ‘orange’ alert (meaning : be prepared) over Gujarat, west Madhya Pradesh, Madhya Maharashtra, Konkan, Gia, coastal and interior Karnataka, Kerala, Telangana, Andhra Pradesh and Odisha. Whereas on the same day, a ‘yellow’ alert prevails ahead of thunder, lightning and heavy rainfall over Uttarakhand, Himachal Pradesh, Uttar Pradesh, Vidarbha, east Madhya Pradesh, Chhattisgarh and West Bengal.
• During the weekend, the whole of south peninsular India, except Tamil Nadu, and central India will receive heavy rainfall with some areas also experiencing lightning and thunder.
• From Thursday, rainfall activity will extend further to the Himalayan states and northwest India regions as well. Thursday onwards, Rajasthan, Haryana, Punjab, west Uttar Pradesh, and Uttarakhand will experience enhanced rainfall activity. In view of the fresh low pressure system set to form in the Bay of Bengal on July 19, rainfall over Odisha, coastal Andhra Pradesh and Telangana will improve.
• Overall, the monsoon will continue to remain active and bring copious amounts of rainfall during the next ten days over all regions of the country, barring Jammu and Kashmir and adjoining areas in northern India. Thereafter, rainfall activity over large parts of the country will be subdued in early August.