APPROACH TO ESTABLISH THE FREQUENCY AND MAGNITUDE OF LANDSLIDE-TRIGGERING RAINSTORM EVENTS IN NEW ZEALAND

T. Glade (Research School of Earth Sciences, Victoria University, PO Box 600, Wellington, New Zeland)

Landslide erosion has an established history in New Zealand. Accessibility of historical and recent landslide information on a national scale is difficult. Collection, storage, and handling of landslide data by affected organisations and institutions is not standardized and strongly dependent on specific investigation purposes.

Frequency and magnitude analysis based on historical records of landslide-triggering rainstorms demonstrate that:

1. landslides are a nationwide problem;

2. recognition and recording of these events is strongly dependent on public awarness and therefore related to population size and extent of urbanised areas; and

3. deforestation increases the frequency of landslide processes, but not necessarily the total magnitude.

However, some regions are more frequently and strongly affected than others. Landslide occurrence in time and space within representative study areas is correlated with climatic time series data. Different regional hydrological thresholds for landslide trigger are established.