Satellite-based emergency mapping using optical imagery: experience and reflections from the 2015 Nepal earthquakes

Abstract

Abstract. Landslides triggered by large earthquakes in mountainous regions contribute significantly to overall earthquake losses and pose a major secondary hazard that can persist for months or years. While scientific investigations of coseismic landsliding are increasingly common, there is no protocol for rapid (hours-to-days) humanitarian-facing landslide assessment and no published recognition of what is possible and what is useful to compile immediately after the event. Drawing on the 2015 M w 7.8 Gorkha earthquake in Nepal, we consider how quickly a landslide assessment based upon manual satellite-based emergency mapping (SEM) can be realistically achieved and review the decisions taken by analysts to ascertain the timeliness and type of useful information that can be generated. We find that, at present, many forms of landslide assessment are too slow to generate relative to the speed of a humanitarian response, despite increasingly rapid access to high-quality imagery. Importantly, the value of information on landslides evolves rapidly as a disaster response develops, so identifying the purpose, timescales, and end users of a post-earthquake landslide assessment is essential to inform the approach taken. It is clear that discussions are needed on the form and timing of landslide assessments, and how best to present and share this information, before rather than after an earthquake strikes. In this paper, we share the lessons learned from the Gorkha earthquake, with the aim of informing the approach taken by scientists to understand the evolving landslide hazard in future events and the expectations of the humanitarian community involved in disaster response.

Simple rules to minimise exposure to coseismic landslide hazard

“…The accuracy of landslide inventories depends on the quality of the imagery from which they are mapped and on subjective judgements by the mappers (Williams et al, 2018). For example, there are uncertainties associated with landslide distinction and amalgamation (Marc and Hovius, 2015;Tanyas et al, 2017) and the definition of the downslope boundary of each landslide.…”

Sentinel-1 SAR Amplitude Imagery for Rapid Landslide Detection

“…In Chile, the first cloudless image available in the service after a landslide occurred in Santa Lucia the 16 December 2017 is on the 10th of January (25 days later with 12 available images). Direct consequences can be like in the 2015 Nepal and 2016 Ecuador earthquakes crises where the unavailability of optical images hampered the capacity of the emergency response coordinators to properly cope with the event [20,21]. The use of Synthetic Aperture Radar (SAR) amplitude images can mitigate the cloud coverage issue, since the SAR signal is capable of imaging the ground surface day and night and in all weather conditions.…”

The State of Remote Sensing Capabilities of Cascading Hazards Over High Mountain Asia

“…One tremendous set of event-based catalogs over HMA are landslide inventories mapped following the 2015 Nepal Earthquakes. Many of these are publicly available, including Kargel et al (2016) (4,312 landslides), Williams et al (2018) (5,578 landslides), Martha et al (2017) (15,551 landslides), Roback et al (2018) (24,915 landslides), andTiwari et al (2017) (14,670 landslides). Other basin-specific inventories are freely accessible over the transboundary Koshi basin (5,653 landslides) .…”