Agriculture and forestry impact assessment for tephra fall hazard: fragility function development and New Zealand scenario application

Abstract

Developing approaches to assess the impact of tephra fall on agricultural and forestry systems is essential for informing effective disaster risk management strategies. Fragility functions are commonly used as the vulnerability model within a loss assessment framework and represent the relationship between a given hazard intensity measure (HIM; e.g. tephra thickness) and the probability of impacts occurring. Impacts are represented using an impact state (IS), which categorises qualitative and quantitative statements into a numeric scale. This study presents IS schemes for pastoral, horticultural, and forestry systems, and a suite of fragility functions estimating the probability of each IS occurring for 13 sub-sectors. Temporal vulnerability is accounted for by a ‘temporality/seasonality coefficient,’ and a ‘fluoride toxicity coefficient’ is included to incorporate the increased vulnerability of pastoral farms when tephra is high in leachable fluoride. The fragility functions are then used to demonstrate a deterministic impact assessment with current New Zealand exposure.