KATHMANDU, NOVEMBER 14
The 2015 earthquakes caused devastation across vast areas of Nepal, killing almost 9,000 people and leaving 3.5 million others homeless.
However, it also triggered thousands of landslides that caused additional destruction to communities and infrastructure, and prompted the occurrence of landslides in the subsequent monsoon season at steeper and higher hill slopes than in average years.
These are the findings of a new research led by scientists from the University of Plymouth and the University of East Anglia (UK).
The study was developed using a database of almost 13,000 recorded monsoon-triggered landslides spanning a period of almost 30 years. This time period included several years known to have been impacted by extreme events such as storms, the 2015 earthquakes and floods, and offered a unique opportunity to assess how landslide occurrence changes through space and time in response to both extreme weather and earthquakes.
The results of the recently published report showed that landslide distributions varied significantly over a period of 30 years, particularly in the years impacted by the storms (1993 and 2002), earthquakes (2015) and floods (2017).
According to the report, landslides currently accounts for 17 percent of all fatalities due to natural hazards.
A World Bank research suggests that more than 66 million people live in landslide-prone regions. This study highlights the compelling need to improve current landslide risk models to better manage and mitigate landslide-induced hazards.
Joshua Jones, the study's lead author, said, "Landslides continue to pose a major hazard to the communities worldwide, particularly those in dynamic, high-mountain regions.
The current models used to assess landslide susceptibility assume that landslide distributions don't change through time. This assumption is largely accepted as scientists are rarely able to obtain enough landslide data to systematically look at how landslide distributions actually vary through time.
"The novelty of this study is that with a new 30-year database, we show that this assumption doesn't actually hold true, with landslide distributions changing significantly in response to extreme weather and earthquakes.
Furthermore, we show that the current susceptibility models cannot accurately account for these changes, suggesting that better time-dependent models are required to improve landslide forecasting and hazard management," Jones added.
This region of Nepal was selected as the focus for the research for several reasons. Its dynamic geology, high topography and monsoonal climate make landslides in this region extremely pervasive, with an average of 78 landslide-related fatalities per year. As such, the country can directly benefit from an improved understanding of landslide susceptibility.
Furthermore, this particular region has experienced several extreme events over the past three decades, thereby presenting a unique opportunity to investigate how landslide spatial distributions vary in response to a wide range of processes.
In examining the landslide database, the researchers looked at 17 possible contributing factors, including elevation, slope angle, bedrock geology, distance to channels or roads, and both peak and average rainfall levels.
Sarah Boulton, associate professor in Active and Neotectonics at the University of Plymouth, said, "Tragically, landslides continue to pose significant risk to populations worldwide, especially when combined with other extreme events such as earthquakes or storms."
"Our new research highlights that in Nepal, during these multi-hazard events, the characteristics of the resulting landslides are different from those produced during a typical monsoon season triggered by rainfall alone. These new data potentially allow to develop more accurate landslide models, which could help save lives," Boulton added.
A version of this article appears in the print on November 15, 2021, of The Himalayan Times.
