It's raining tears in the hills: 21% above normal rainfall in Uttarakhand
Monsoon trough is a feature of monsoon circulation that typically passes over the Indo-Gangetic plains, but its northward movement shifted it towards the Himalayan foothills, leading to heavy rainfall
The recent heavy rains in Uttarakhand, which resulted in multiple deaths and significant damage to infrastructure, can be attributed to the northward movement of the monsoon trough and its interaction with a weak western disturbance.
Landslides, building collapses, and road damage were reported as a result of these extreme weather conditions.
The monsoon trough, a low-pressure area that stretches from Pakistan to the Bay of Bengal, is a semi-permanent feature of monsoon circulation, according to the India Meteorological Department.
It typically passes over the Indo-Gangetic plains, but its northward movement shifted it towards the Himalayan foothills, leading to heavy rainfall in the region.
Experts have noted that the Himalayan and northeastern states have experienced heavy rain since August 7, causing soil loosening, erosion, and flash floods in Uttarakhand and Himachal Pradesh.
In this period, Uttarakhand recorded 232.5mm of rain, which is 21 per cent more than the normal average of 191.40mm.
M Mohapatra, IMD Director General, stated that the feeble western disturbance further intensified the impact of heavy rain in the region.
However, he also predicted that the monsoon trough’s southward shift would temporarily reduce rainfall in the hills and increase rainfall over east-central India. This change in weather patterns is expected to take effect from Tuesday.
“The monsoon trough is north of its normal position. It’s over the Himalayan foothills. This region has been receiving heavy rain for a week now, so it’s also accumulated. On Sunday, a feeble western disturbance also interacted with the monsoon trough, and it is continuing to interact on Monday also.
“The monsoon trough will gradually shift southward now temporarily which will lead to reduction of rainfall over the hills and increase in rainfall over east-central India,” said Mohapatra. He predicted that the rain over both states will reduce from Tuesday.
“During the monsoon breaks monsoon trough shifts north close to foothills which produces heavy rains over the hills and northeast India. Nepal also gets good rain. This was expected in general,” said M Rajeevan, former secretary, ministry of earth science.
The latest spell of heavy rainfall was caused due to northward movement of the axis of the monsoon trough, making weather conditions favourable for heavy to very heavy rains across the Himalayas.
Explaining the phenomenon, Akshay Deoras, Meteorologist and Research Scientist with the National Centre for Atmospheric Science and Department of Meteorology, University of Reading, Britain, said: “During break-monsoon conditions, most monsoon rainfall activities get focussed over Himalayan foothills and to an extent over Himachal Pradesh and Uttarakhand.
“At the same time, other parts of the country, like Central India, witness dry weather conditions. This is not new and has been happening ever since the existence of monsoon. The science of global warming is clear that if we continue to emit more and more greenhouse gases into the atmosphere, especially CO2, it will enhance the air’s capacity to hold more and more water.
“Now, whenever favourable weather conditions appear, for example, in the case of break monsoon conditions, the air will release much more water vapour in the form of rainfall. This means the probability of an ordinary rainfall event intensifying into a heavy or extremely heavy one will increase because of global warming.”
Mahesh Palawat, Vice President- Meteorology and Climate Change, Skymet Weather, said more warming means more energy in the environment, leading to more rain.