Earthquakes and landslides in Nepal / Nepal landslide mapping

Role in SHEAR

Improving risk knowledge and preparedness for landslides in Nepal.

Context

In 2015, earthquakes triggered over 22 000 landslides across 14 districts of central Nepal. In the aftermath of the earthquake, the National Reconstruction Authority (NRA) identified approximately 500 settlements that required field-based geohazard assessments prior to permitting reconstruction.

The damage to the hillslopes during the earthquakes has resulted in an increased probability of landsliding during the following monsoon seasons (2015 onwards). This is anticipated to last for five to ten years, and is likely to have a major impact on the road network, reconstruction, and personal safety.

There is limited coordinated effort to assess post earthquake landslide hazard, in particular the evolving landslide risk due to the monsoons. Moving beyond planning based only on a static assessment of current risk is vital, and NRA activities depend on this information.

Organisations

News

Resources

Post earthquake landslide mapping

The BGS and partners at Durham University have used satellite imagery to map and characterise over 3000 landslides triggered by the 2015 earthquake. Various types of satellite data (obtained via the International Charter: Space and Major Disasters, and directly from data suppliers) including WorldView, UK-DMC2, SPOT, Pleiades and RADARSAT-2 to create maps of landslides active since the earthquake. These maps are helping the relief efforts by showing where roads or rivers are blocked and where villages have been affected by landslide debris.

The UK team has also worked alongside and compiled the landslide maps from other agencies, such as NASA, NGA, MDA and ICIMOD, to produce a comprehensive map of the post earthquake landslides. The maps have been posted in several locations including the Charter website, UNOSAT, Nepal Earthquake Support and Earthquakes Without Frontiers, and are being used on the ground by several relief agencies.

Landslide mapping and modelling

Aims

  • Mapping the developing landslide situation in central Nepal between 2015 and 2018.
  • Using these data to generate an up-to-date, district-scale landslide risk assessment, to feed into the NRA for planning and programming.
  • Promoting the outputs of this work with those agencies tasked with managing landslide risk in Nepal.

Approach

Freely available medium-resolution and commercial high-resolution satellite imagery is used to build on post earthquake national inventory, and complete post-2015 to post-2018 monsoon-triggered landslide inventories in all 14 earthquake-affected districts.

A set of landslide demonstration sites identified as 'high risk' by the NRA geohazards risk assessment is being established, to collect detailed, time-series landslide monitoring data.

Detailed mapping using very high-resolution commercial imagery of the changing nature of landsliding on critical highways between Kathmandu and the borders with India and China is being undertaken. This mapping effort will be repeated for post earthquake conditions, and then after each following monsoon.

Landslide susceptibility modelling and scenario analysis is being undertaken, focusing on modelling future rainfall-triggered landsliding impacts in the 14 earthquake-affected districts.

Landslide risk assessment to individual house locations, footpaths, roads and infrastructure during future monsoons using a range of scenarios between, and including, best and worst cases is being conducted; this will enable prioritisation for resource management, and identification of areas of perpetually high risk.

Innovation

The project explores how quickly manual, satellite-based, emergency mapping can be used to carry out a humanitarian-facing landslide assessment in the immediate aftermath of a co-seismic event in order to generate useful information.