Leanne Webb

Climate change, viticulture, and wine: challenges and opportunities.

Throughout human existence weather and climate have played a decisive role in where and how cultures have developed. Agricultural systems that could support early civilizations were crucial to their success. Nomadic tribes have always moved to find better growing conditions for their crops or to feed their animals. During the age of worldwide exploration the suitability of a given location to certain crops helped to determine whether a colony could be established there or not. Today, as in the past, climate is clearly a pervasive factor in the success of all agricultural systems, influencing whether a crop is suitable to a given region, largely controlling crop production and quality, and ultimately driving economic sustainability. Maybe more so than at any time in human history, our agricultural systems today are at risk from rapidly changing climates that affect the suitability and sustainability of crops worldwide. Climate’s influence on agribusiness is at its most evident with viticulture and wine production where it is arguably the most critical aspect in ripening fruit to its optimum to produce a desired wine style. As in the past, today’s wine production occurs over relatively narrow geographical and climatic ranges, most often in midlatitude regions that are prone to high climatic variability. Furthermore, individual winegrape varieties have even narrower climate ranges, which further limit the areas suitable for their cultivation. These narrow niches for optimum quality and production put the cultivation of winegrapes at greater risk from both short-term climate variability and long-term climate changes than other crops. And while winegrapes as a crop are not crucial to human survival, the vine’s extraordinary sensitivity to climate makes the industry a strong early-warning system for problems that all food crops may confront as climates continue to change. This special issue of the Journal of Wine Research, along with further supplemental papers in the next issue, is devoted to examining the significance of climate change to growing grapes for wine production. Articles in the two issues provide perspectives on the physical basis for climate’s influence, vulnerabilities of differing sectors of the industry, and available mitigative and adaptive strategies. In this issue, Schultz and Jones detail how climate change has altered grape composition and wine styles and show that the geography of wine regions globally is changing and will likely continue to change in the future. Examining climate in Australia and China, Pagay and Pullman in the next issue detail how both regions have experienced increased heat extremes and below average precipitation that has lead to more frequent and severe droughts. Other research in Australia has coupled these observations with projections

Impact of future warming on winter chilling in Australia

Increases in temperature as a result of anthropogenically generated greenhouse gas (GHG) emissions are likely to impact key aspects of horticultural production. The potential effect of higher temperatures on fruit and nut trees’ ability to break winter dormancy, which requires exposure to winter chilling temperatures, was considered. Three chill models (the 0–7.2°C, Modified Utah, and Dynamic models) were used to investigate changes in chill accumulation at 13 sites across Australia according to localised temperature change related to 1, 2 and 3°C increases in global average temperatures. This methodology avoids reliance on outcomes of future GHG emission pathways, which vary and are likely to change. Regional impacts and rates of decline in chilling differ among the chill models, with the 0–7.2°C model indicating the greatest reduction and the Dynamic model the slowest rate of decline. Elevated and high latitude eastern Australian sites were the least affected while the three more maritime, less elevated Western Australian locations were shown to bear the greatest impact from future warming.

Managing Grapevines through Severe Heat: A Survey of Growers after the 2009 Summer Heatwave in South-eastern Australia

A survey of 92 vineyards, representing 10 winegrowing regions in south-eastern Australia, soon after exposure to a severe heatwave, revealed variation in the reported heat-related impact. This variation was observed between regions, within regions and within vineyards. Notably the estimates of losses were not always related to the amount of heat above a certain threshold but to the management practices employed in the lead-up and through the event. Applicable and achievable recommendations for managing severe heat events have resulted from this assessment. We believe this method of capturing information from the diverse knowledge-base of managers is a very effective way to reveal potential adaptive capacity to a changing climate.

Challenges in predicting climate change impacts on pome fruit phenology

Climate projection data were applied to two commonly used pome fruit flowering models to investigate potential differences in predicted full bloom timing. The two methods, fixed thermal time and sequential chill-growth, produced different results for seven apple and pear varieties at two Australian locations. The fixed thermal time model predicted incremental advancement of full bloom, while results were mixed from the sequential chill-growth model. To further investigate how the sequential chill-growth model reacts under climate perturbed conditions, four simulations were created to represent a wider range of species physiological requirements. These were applied to five Australian locations covering varied climates. Lengthening of the chill period and contraction of the growth period was common to most results. The relative dominance of the chill or growth component tended to predict whether full bloom advanced, remained similar or was delayed with climate warming. The simplistic structure of the fixed thermal time model and the exclusion of winter chill conditions in this method indicate it is unlikely to be suitable for projection analyses. The sequential chill-growth model includes greater complexity; however, reservations in using this model for impact analyses remain. The results demonstrate that appropriate representation of physiological processes is essential to adequately predict changes to full bloom under climate perturbed conditions with greater model development needed.

Climate Change: Horticulture

The climate conditions for world horticultural regions are projected to change. Farmers will be required to cope with increasing temperatures, changes to water availability, lack of winter chilling and increased extreme weather exposure. Compared with other agricultural pursuits, horticulture remains particularly exposed due to higher infrastructure and set-up costs and a lack of temporal and spatial flexibility in farming practices. Some regions may benefit from these climatic changes and become better suited to growing horticultural crops whereas in sites where the climate is already at the hotter end of the growing spectrum, continuing production may be judged too risky.

A robust impact assessment that informs actionable climate change adaptation: future sunburn browning risk in apple

Climate change impact assessments are predominantly undertaken for the purpose of informing future adaptation decisions. Often, the complexity of the methodology hinders the actionable outcomes. The approach used here illustrates the importance of considering uncertainty in future climate projections, at the same time providing robust and simple to interpret information for decision-makers. By quantifying current and future exposure of Royal Gala apple to damaging temperature extremes across ten important pome fruit-growing locations in Australia, differences in impact to ripening fruit are highlighted, with, by the end of the twenty-first century, some locations maintaining no sunburn browning risk, while others potentially experiencing the risk for the majority of the January ripening period. Installation of over-tree netting can reduce the impact of sunburn browning. The benefits from employing this management option varied across the ten study locations. The two approaches explored to assist decision-makers assess this information (a) using sunburn browning risk analogues and (b) through identifying hypothetical sunburn browning risk thresholds, resulted in varying recommendations for introducing over-tree netting. These recommendations were location and future time period dependent with some sites showing no benefit for sunburn protection from nets even by the end of the twenty-first century and others already deriving benefits from employing this adaptation option. Potential best and worst cases of sunburn browning risk and its potential reduction through introduction of over-tree nets were explored. The range of results presented highlights the importance of addressing uncertainty in climate projections that result from different global climate models and possible future emission pathways.