A volcanic tephra fall hazard evacuation decision support tool for Taranaki dairy livestock using probabilistic modelling (2016)
AuthorsWild, Alecshow all
The dairy industry is one of New Zealand’s leading economic drivers, contributing $18.1 billion in export revenue in the 2013/14 financial year. However, past experiences have demonstrated that dairy livestock are vulnerable to the e↵ects of volcanic tephra fall as it can: 1) directly impact animal health; 2) contaminate feed; 3) contaminate water; and 4) disrupt support services and infrastructure. Problematically, approximately 10% of New Zealand’s dairy livestock are located in the Taranaki region, within 45 km of Mt. Taranaki, an active volcano capable of producing large explosive eruptions with widespread tephra fall. Understanding the consequences of tephra fall is necessary to inform risk management strategies. This research conducts a risk assessment to evaluate livestock welfare impacts from Mt. Taranaki tephra fall and develops a livestock evacuation decision support tool. This provides a simplified method to evaluate whether the potential benefits of evacuation outweigh the potential consequences if no evacuation takes place, something that has not previously been conducted for livestock evacuation decision-making. The risk assessment combines a geospatial exposure inventory, a probabilistic volcanic hazard assessment (PVHA) for tephra fall and a vulnerability model to determine impact to livestock welfare. The geospatial exposure inventory represents farm characteristics including; livestock population, the power supply network, water supply, transportation network, and demonstrates the complex interrelationships of farms with external services. The PVHA integrates a probabilistic tephra dispersal model (TEPHRA2) into a Bayesian Event Tree for Volcanic Hazards (BET VH). This allows for long-term tephra fall hazard modelling while incorporating multiple levels of uncertainty. Results demonstrate that to fully comprehend the hazard, both large explosive and smaller more frequent eruptions need to be modelled. Vulnerability is assessed through fault-tree analysis for farms and supporting critical infrastructure. Livestock welfare is measured by the ability to provide: 1) nutrition; 2) water; and 3) milking. A reduction in any of these has been assumed will impact livestock welfare. The results of the risk assessment are annualised probabilities of livestock welfare impact per Taranaki farm. Findings indicate that following an eruption, approximately 780 farms have a 50% chance of being impacted to an extent which results in decreased livestock welfare. While only farms directly exposed to tephra fall are likely to experience feed shortages, farms outside the tephra fall depositional area can expect to experience water shortages and inability to milk due to tephra impacting water supplies. The most vulnerable water supply sources across the region are municipal schemes because their catchments are most likely to be impacted by tephra fall. Lastly, water supply is dependent on pumping facilities which could also be impacted by tephra fall-induced power outages. An evacuation decision support tool was developed using a cost-benefit analysis approach. This evaluates evacuation viability both pre- and post-eruption. Pre-eruption assessment uses two approaches: 1) an eruption probability timeline scenario; and 2) by modifying a BET VH for eruption forecasting. Findings indicate that livestock evacuation may be advantageous to protect livestock welfare prior to large explosive eruptions given sufficient warning time. However, this requires substantial logistical organisation and transport resources, along with the ability to accommodate relocated livestock, without which evacuation is unlikely to be feasible. This research provides the first quantitative geospatial inter-dependency study for the Taranaki dairy industry from tephra fall, providing a framework for future studies.