Linking global circulation model outputs to regional geomorphic models: a case study of landslide activity in New Zealand

Abstract

General circulation models (GCMs) were constructed for future projections of circula- tion patterns on a global scale. IPCC emission scenarios, adopted by GCMs, suggest that climate change is due to anthropogenic emissions of greenhouse gases. Application of GCMs to regional- scale studies is difficult due to the different spatial resolutions. Downscaling techniques transfer GCM results to larger scales. Rainfall-triggered landslides are a worldwide phenomenon and can cause socio-economic problems. Regional models of these geomorphic processes were linked to regionalized GCM outputs for New Zealand. Climate-model outputs from HadCM2SUL were used to produce precipitation and temperature scenarios via analog downscaling. Climate-impact studies have rarely been developed for New Zealand. For both Wellington and Hawke's Bay, climate-change scenarios were applied to 3 deterministic landslide models (the daily rainfall model, the antecedent daily rainfall model and the antecedent soil water status model). All of them relate landslide occur- rence to climate conditions. Results give a more reliable projected probability change of landslide occurrence for Wellington than for Hawke's Bay. Wellington's cold-season precipitation is mostly associated with synoptic weather systems depending on large-scale circulation features, captured using the downscaling procedure. In contrast, Hawke's Bay receives its peak precipitation from fre- quent high-magnitude storms. Common to all 3 applied landslide models for both regions is the trend of decreased landslide activity for the target period, 2070-2099.