Meteorological agencies link Nepal floods to convergence of monsoon systems over India

Recent deadly floods and landslides that impacted Nepal through Tuesday and Wednesday were driven by a vigorous monsoon system, according to the Beijing centre of the World Meteorological Organisation (WMO). The severe weather was intensified by a low-pressure area located over south Uttar Pradesh and adjoining north-east Madhya Pradesh.

While the WMO centre classified the system as a monsoon depression, the India Meteorological Department (IMD) described it as a conventional monsoon 'low' originating over the Bay of Bengal. On Wednesday, the IMD located this 'low' over south Uttar Pradesh and adjoining north-east Madhya Pradesh, with its influence amplified by a monsoon trough stretching from Jammu through Dehradun and Shahjahanpur, across the centre of the 'low,' and onward through Ranchi and Digha into the north-east Bay.

This trough functioned as a moisture highway, feeding humid air directly into the storm zone. A secondary trough extended from the 'low' towards the north-east Bay, crossing East Madhya Pradesh, Chhattisgarh, and Odisha. Additionally, a western disturbance represented by a cyclonic circulation over north Haryana interacted with the system to increase rainfall.

The combined weather systems directed successive waves of rain into the Himalayan foothills and mountains. This produced heavy rainfall over Nepal and extremely heavy rain over West Uttar Pradesh on the Indian side until Wednesday morning. East Uttar Pradesh and East Madhya Pradesh also recorded heavy to very heavy rain.

The broader rain belt impacted large parts of North-West and East India, including the hills and plains of West Bengal, Bihar, Haryana-Chandigarh-Delhi, Himachal Pradesh, East Rajasthan, and West Madhya Pradesh. Heavy rain was also logged in Coastal Karnataka, Kerala, and Mahe in the South Peninsula. Despite the widespread downpour, the cumulative rainfall has not yet reduced India's overall monsoon deficit, which remained at 13 per cent on Wednesday with a week remaining in August.

The current 'low' may move back towards the Bay of Bengal, where it could potentially generate a successor system. This successor 'low' might strengthen into a depression over land, setting up another spell of heavy rain across East, North-East, Central, and North-West India.

The WMO Beijing centre noted that Nepal has endured persistent rain for about 10 days. Accumulated rainfall reached heavy to intense levels as the vigorous monsoon combined with orographic lifting along the southern Himalayan foothills. Rainfall over the upstream Tibetan plateau in southern Tibet, China, further contributed to flash floods and debris flows in northern Nepal.

The threat remains active as the 'low' is expected to continue generating moderate to heavy rain over Nepal for the next three days, with heavy to intense downpours likely in the southern parts of the country. Rain is expected to persist across East India, Nepal, and Bangladesh for the next five days. The WMO has urged vigilance against secondary disasters, including flash floods, landslides, and debris flows.

"Extreme weather events and cross-border weather systems present significant operational and logistical challenges for businesses operating in logistics, supply chain, and regional trade. Companies with exposure to affected areas in North and East India, as well as neighboring regions, must incorporate robust disaster management and continuity planning into their business strategies to mitigate supply disruptions caused by infrastructure damage and transport delays." — Dr. Shishir Gupta, Founder & CEO, StartupLanes