Farmers will soon be able to get advanced warning of where ash might fall following a volcanic eruption.

GNS Science, MetService and the Earthquake Commission have joined forces to enhance real-time forecasting models for volcanic ash-fall from the country's 10 most active volcanoes.

Apart from the obvious physical danger posed by proximity to large eruptions, ash is the most significant effect on agriculture.

The new project combines existing eruption scenarios with weather forecasting to predict the likelihood of an area being affected by volcanic ashfall.

'New Zealand is dotted with active volcanoes and an eruption could impact communities far beyond the regions closest to the volcano,” says Taupo based GNS Science volcanologist Dr Yannik Behr.

'Power companies need to know the risk of flashovers due to ash, NZTA needs to know if the markings on the roads will become invisible and dairy farmers will be interested in how much ash their cows may be ingesting from the grass.”

The project team is developing models that will be able to provide more accurate estimates of how much ash will land, but also when it is likely to arrive.

Dr Behr says in previous eruptions GNS Science would traditionally focus on ash deposits, while MetService would focus on aviation impacts, as was the case when eruptions at Ruapehu in 1995 and Tongariro in 2012 significantly affected air travel over New Zealand.

MetService scientist Dr Rosa Trancoso says that Metservice has been working with GNS Science since 2014 to combine modelling forecasts with GNS Science data for New Zealand's 10 most active volcanoes. The new project will advance this work by providing the chance of ash being present in a particular area, following an eruption.

'The new tool will be valuable to inform the affected communities about the probability of ash falling in their area, and whether it is light or heavy.”

EQC's manager of research, Dr Natalie Balfour, says the team's work will bring a significant advance in helping communities understand the impact volcanic activity could have during an eruption.

'A better model for ash-fall forecasting means decision-makers like emergency managers, councils and homeowners will have more accurate information about the likelihood and severity of ash-fall in their area, so that they can take appropriate action.

'Depending on weather, ash can travel long distances and impact communities who may not normally consider themselves at risk from the impacts of an eruption,” says Dr Balfour.

A Beef and Lamb fact sheet to farmers lists ash as the biggest threat to agriculture from a volcanic eruption and warns effects can be long lasting with reduced animal weight gain and pasture growth.

'The main concern for farmers will be the immediate physical impacts on stock, contamination of stock water and pastures,” the fact sheet reads.

'Expect clean water to be in short supply, with natural water supplies and dams contaminated, and pump functions severely reduced by the abrasive nature of the ash.”

Following ash falls from Ruapehu in 1995 and 1996, farmers noted that animals were readily put off their feed by two to five millimetres of ash deposits.