KATHMANDU, NOVEMBER 19

Earthquakes and extreme rainfall can lead to a six-fold increase in the rates of rainfall-triggered landslides occurring during Nepal's monsoon season, according to a new research.

The Himalayan nation experiences severe landslides every year as a result of its annual monsoon season, which occurs between June and August. However, the new study conducted by researchers from the University of East Anglia, University of Plymouth, University of Exeter (UK) and international engineering consultancy firm AE- COM (US) explores how extreme rainfall and earthquakes can induce landslide rates above and beyond those seen during a normal Himalaya monsoon season.

By analysing satellite imagery and rainfall data, researchers were able to establish a clear pattern between the strength of the monsoon season and the amount of landsliding over a 30- year period between 1988 and 2018. This revealed that extreme 'cloud outburst' storms in 1993 and 2002 led to around four times as many landslides as would be expected in an average monsoon season.

Similarly, landscape damage caused by the April 2015 Gorkha earthquakes was found to have caused around six times as many rainfall-triggered landslides during the 2015 monsoon season as would be expected.

This landscape damage also caused an increase in the expected numbers of landslides in the 2016 monsoon season, with conditions returning to nearer the average by 2017.

The study report released earlier this week also showed that the most severe landscape damage caused by the 2015 earthquake did not occur right at its epicentre, but in nearby locations where high earthquake peak ground accelerations occurred across particularly steep mountain slopes.

Josh Jones, the study's lead author, said 'Unfortunately, people in Nepal are frequently affected by landslides during the monsoon season, with widespread damage to homes and infrastructure every year. This study shows how much this landslide risk can be increased by extreme rainfall and earthquakes, and for how long those effects can be felt. We hope that this information could be an important tool in helping local communities plan for future landslide hazard, particularly following large earthquakes.'

Sarah Boulton, associate professor in Active and Neotectonics at the University of Plymouth, added, 'Once unusual rainfall and flood events are already becoming more frequent globally as a result of our changing climates. Climate models indicate that Nepal is likely to experience increased storminess and potentially higher levels of annual rainfall in the future.'

Michael Whitworth, an associate director at AECOM, said, 'This project shows the benefits of collaborative work between industry and academia. The results of this research can inform disaster risk reduction in vulnerable areas, leading to better planning and mitigation against landslide hazards caused by infrequent large events such as earthquakes.'

A version of this article appears in the print on November 20, 2021, of The Himalayan Times.