Agriculture and forestry impact assessment for tephra fall hazard

Heather Craig,Carol Stewart,Alec J. Wild,Christina Magill,Thomas Wilson

doi:10.30909/vol.04.02.345367

Abstract

Developing approaches to assess the impact of tephra fall to 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 (e.g., tephra thickness) and the probability of impacts occurring. Impacts are represented here 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 ‘seasonality coefficient,’ and a ‘chemical toxicity coefficient’ is included to incorporate the increased vulnerability of pastoral farming systems when tephra is high in fluoride. The fragility functions are then used to demonstrate a deterministic impact assessment with current New Zealand exposure.

Highlights

Assessing the extent and severity of agricultural and forestry impacts from tephra fall hazards and their causal mechanisms is essential when developing disaster risk management strategies
In order to accurately undertake risk assessments, a quantified understanding of the following is required: 1) hazard intensity metrics (HIMs) and spatial constraints; 2) identification of exposed elements; and 3) the vulnerability of exposed elements to the hazard
There have been limited attempts to undertake agricultural and forestry risk assessments for tephra fall with previous studies focused on creating generalised models covering a broad range of agricultural and forestry systems, where impacts typically increase as tephra thicknesses or loading reach a hazard intensity threshold [Jenkins et al 2014a; Jenkins et al 2014b], or fragility functions were proposed from relatively limited datasets and expert judgement [Wilson and Kaye 2007]

Summary

Introduction

Assessing the extent and severity of agricultural and forestry impacts from tephra fall hazards and their causal mechanisms is essential when developing disaster risk management strategies. Previous studies have identified that tephra fall impacts on agriculture and forestry will be determined by the exposed farm characteristics, climate, time of year, vegetation/crop type and morphology, existing risk management and the wider ecological system properties and health, in addition to the type, volume and duration of tephra fall [Cook et al 1981; Cronin et al 1998; Wilson and Kaye 2007; Wilson et al 2011a] This complexity in vulnerability is not well considered in available volcanic impact and risk assessment tools. There have been limited attempts to undertake agricultural and forestry risk assessments for tephra fall with previous studies focused on creating generalised models covering a broad range of agricultural and forestry systems, where impacts typically increase as tephra thicknesses or loading reach a hazard intensity threshold [Jenkins et al 2014a; Jenkins et al 2014b], or fragility functions were proposed from relatively limited datasets and expert judgement [Wilson and Kaye 2007]

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Conclusion