Agricultural fragility estimates for volcanic ash fall hazards

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Wilson, T.M.; Kaye, G.D. 2007 Agricultural fragility estimates for volcanic ash fall hazards. Lower Hutt, N.Z.: GNS Science. GNS Science report 2007/37 51 p.

Abstract: This report presents estimates of expected damage (fragility functions) to the agricultural sectors of pastoral farming, horticulture, and forestry in New Zealand when they are subjected to volcanic ash fall hazards of varying intensities. The fragility functions are derived from a combination of 1) literature review of existing fragility estimates, 2) development of new functions based on consultation with agriculture and volcanic hazards experts in New Zealand, 3) field observations of impacts to agriculture from the 2006 eruption of Merapi volcano in Indonesia and, 4) preliminary results from field and laboratory trials investigating the impact of volcanic ash on pastures. Volcanic ash thicknesses that cause 1, 20, and 90% damage to each commodity class are presented, along with a Weibull curve derivation methodology to derive the functions. Different functions are given for production loss (loss of valuable commodity produced by the farm, e.g. milk or fruit) and asset loss (non-saleable assets on the farm, e.g. milking sheds or grape vines). This differentiation recognises the different resilience of the many separate components of agricultural production and farming assets on New Zealand farms. The changing climate through out the year has a significant influence on which activities and processes are preformed at particular times of the year on New Zealand farms. These seasonal influences change vulnerability in each agricultural sector and have been identified as an important component in determining fragility of agricultural commodities to an ashfall. The functions provided here are thusly weighted with a seasonality co-efficient specific to each agricultural sector. Summary values of the different agricultural sectors are provided based on Ministry of Agriculture and Forestry statistics to create a baseline for future agricultural volcanic loss estimation. Theoretical examples of scenario ash fall events at the Okataina Volcanic Centre is given to illustrate the application of the provided fragility functions. (auth)