20 October 2021
A very late sting in the tail of the South Asian monsoon
Posted by Dave Petley
A very late sting in the tail of the South Asian monsoon
As I have noted previously, the dominant continental scale meteorological phenomenon for landslides globally is the South Asian summer (SW) monsoon. In a normal year this develops in early June and withdraws through September. Heavy monsoon rainfall in mid October is not the norm.
But this year the summer monsoon has had a very nasty sting in the tail. Earlier this week I wrote about the serious landslides and floods in the Kerala area over the weekend. In the last couple of days it has been the high mountains of India and Nepal that have been affected.
In Nepal the rainfall has been very serious. The Department of Hydrology and Meteorology tweeted data and a map of rainfall totals across the country:-
#48hours_total_precipitation
Most parts of Sudurpachchim province received precipitation of more than 150 mm in 48 hours. A station in Dadeldhura district recorded 502.2 mm in 2 days. For real time rainfall information, pls visit https://t.co/xfWfmbmEq3#Flood #landslide #Nepal pic.twitter.com/AxJPiQp7Ya— Climate Analysis Section_DHM (@ClimateDhm) October 19, 2021
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In Dadeldhura District in the west of Nepal rainfall totals on 18-19 October exceeded 500 mm. The consequences across the country are all too predictable – the Kathmandu Post reports that at least 18 people have been killed and a further 24 people are missing, with reports still coming in. This includes a probable debris flow that killed four people in Doti and three people killed in a landslide in Baitadi. The worst event might have occurred in Dikla village of Thalara Rural Municipality, Bajhang, where 24 people are reported missing in a landslide that buried seven houses.
Dr Basanta Raj Adhikari tweeted a video of landslides on the famous Dharan-Dhankuta highway, which is the best engineered mountain road in Nepal:
A number of landslides have blocked the Dharan-Dhankuta Road. pic.twitter.com/vvFvH2tyHK
— Dr. Basanta Raj Adhikari (@basanta58_raj) October 19, 2021
Meanwhile, in Uttarakhand in India the late monsoon rainfall has also had a devastating impact. Reports indicate that at least 47 people have been killed, with more reported missing. A serious incident occurred at the Ramgarh area of Bhawali Tehsil, Nainital, where a landslide killed nine people. India Today has this image of a landslide on the Askote-Jauljibi road in Pithoragarh:–
A monsoon-induced landslide on the Askote-Jauljibi road in Pithoragarh in India. Image from PTI / India Today.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
Its not only the monsoon, that causes landslides. Ass ich can be seen on the picture from the Askote-Jauljibi road, there are already signs of old landsliedes along the roadside. The bigger one was a reactivated slide, which had already occurred after road construction. If retaining measures are missing that will be the result.