Rapid surveillance and assessment of fire damage vineyards

Abstract

In December 2019, a bushfire occurred in the Adelaide Hills, South Australia, where 25,000 hectares were burnt resulting in various degrees of damage. The ability to coordinate and plan recovery after a fire event relies on robust and timely data. The current process to assess damage to vineyards from fire is time consuming, subjective, or semi-quantitative at best. This study compares the rapid assessment and mapping of fire damage using high-resolution satellite imagery with more traditional ground-based measures. Correlations between ground visual fire damage assessments and post-fire NDVI and VARIgreen satellite imagery were significant but ranged from relatively weak to moderate negative correlations. Severely damaged vines had reduced canopy growth, low fertility and low starch concentrations in buds and canes. In contrast, vines that received minor-moderate damage were able to recover within one to two years. Results from this study will allow stakeholders to manage decisions in relation to fire recovery by improving the efficiency and effectiveness of their response.

Summary

There is increasing scientific consensus that climate change is one of the underlying causes of the prolonged dry and hot conditions that have increased the risk of extreme fire weather in many countries around the world.

In December 2019, a bushfire occurred in the Adelaide Hills, South Australia, burning through 25,000 hectares, including some vineyards.  Vineyards and their infrastructure were scorched resulting in damage to varying degrees. The ability to coordinate and plan recovery after a fire event relies on robust and timely data. The current practice for measuring the scale and distribution of fire damage is to walk or drive the vineyard and score individual vines based on visual observation. The process is time consuming, subjective, and semi-quantitative at best. After the December 2019 fires, it took many months to access properties and estimate the area of vineyard damaged. This study compared the rapid assessment and mapping of fire damage using high-resolution satellite imagery with more traditional ground-based measures. Correlations between ground visual fire damage assessments and post-fire NDVI (-0.7 to 0.04) and VARIgreen (-0.333 to 0.074 for only the University of Adelaide trial blocks) satellite imagery were significant but showed no correlation to a moderate or weak negative correlation respectively. 

Canopy growth, vine fertility and starch concentrations were tracked in the two seasons following the fire event to assess vine recovery. Canopy health in the seasons following the fires correlated to the severity of the initial fire damage. Severely damaged vines had reduced canopy growth, were infertile or had very low fertility as well as lower starch concentrations in buds and canes during dormancy, which reduced productivity in the seasons following the bushfire event. In contrast, vines that received minor to moderate damage were able to recover within one to two years.

Delays of 3 to 4 months in gathering the ground truth data set, coordinated in a separate project through Wine Grape Council of South Australia (WGCSA), had an impact upon the reliability of this data relative to the imagery captured immediately post-fire event due to regrowth of the vines. This factor, and the relatively small ground truth data sets, limited the ability to create a reliable multi-class variable damage model. However, several models have been created capable of determining a binary value for damage on known vineyard sites across the fire scar, with relative confidence. In the event of future fires this can be deployed immediately, and a coordinated collection of concurrent ground truth data could help form better data sets for improved accuracy and to develop variable damage models. Tools have been developed that rapidly and affordably capture the extent and severity of damage over large vineyard areas to allow producers, government, and industry bodies to make more efficient decisions during the post-fire recovery. The benefits of this will flow to the grower through better fire recovery planning, coordination and delivery, providing more certainty and reducing stress.