Interferometric Synthetic Aperture Radar (InSAR) and field‐based observations of rainfall‐triggered landslides from the November 2021 storm, Gisborne/Tairāwhiti, New Zealand

Abstract

Gisborne/Tairāwhiti is particularly susceptible to rainfall‐triggered landslides on account of (1) steep slopes, (2) young, soft geology, (3) landuse change effects. The interplay of these factors led to a particularly damaging rainfall‐induced landsliding event during 3–7 November 2021, following >200 mm of rainfall. This caused a Multiple Occurrence Regional Landslide Event, impacting residential properties and infrastructure in the city and rural areas. We report mainly on landslides in Gisborne city and suburbs, based on field reconnaissance and interferometric synthetic aperture radar monitoring of slopes. This highlights prevailing land instability prior to the more recent ex‐Tropical Cyclone Gabrielle (2023).