Climate change in the viticulture sectors: Overview of long term climate trends in the Western Cape (Part 1)

by | Apr 1, 2020 | Viticulture research, Winetech Technical

Annual average temperatures for South Africa from 1901 – 2018. Each stripe highlights the annual temperature difference compared to the long term mean (the first stripe is 1901 and the last stripe is 2018). (Source of graphic: Ed Hawkins. Data source: Berkeley Earth, NOAA, UK Met Offrice, MeteoSwiss, DWD.) #showyourstripes

This article summarises extensive statistical climatic analysis into normalised bar graphs, graphics that better highlight increases and decreases in weather over regions and months.

Land and ocean surface temperatures, continue to increase above the average 132-year record held within the world meteorological organisation. The average surface temperature of the earth has risen by about 0.9°C since the late 19th century, a change driven largely by increased carbon dioxide into the atmosphere. The five warmest years on record taking place since 2010, 2016 being the hottest on record, followed by 2019, 2018, 2017 and 2014 respectively. Not only was 2016 the warmest year on record, but eight of the 12 months that make up the year (January to September, with the exception of June) the warmest on record for those respective months. January 2016 was the hottest January ever recorded, and recently in 2019 June, July and September was the hottest ever recorded for those months. This is globally and locally alarming. The period April 2018 to March 2019 was the warmest 12 month period on record for Europe. Australia recently had its warmest March on record. Africa is one of the continent’s most vulnerable to climate change, regions at lower latitudes are especially vulnerable as they already suffer from intense heat. Climate change on a South African scale based on the annual average temperatures from 1901 – 2018 highlights the warming that is of concern (#knowyourstripes). Scientists continue to highlight the alarming warming trend that stands out from the noise of natural variation that sceptics tend to push on weather phenomenon’s like El Nino, but still we are warmer today than in the 1900’s.

In view of climate change, economic pressures and future limitation of water availability to the agricultural sector, informative decisions regarding the suitability of environments for viticulture are paramount locally and globally. Every local environment has unique diurnal temperature variations due to the inland penetration of the sea breeze and other local effects, such as wind, topography, coastline orientation, slope angle and aspect. Continuous monitoring of extreme environments is hampered by the sparse and/or irregular distribution of meteorological stations, the difficulties in accessing data from government data custodians, the quality of the data is not assured, and data is costly. Our understanding of climate is meteorological variables in a given region over a long period, usually over a 30-year interval, as opposed to weather which is a particular condition at a particular place over a short period of time within years or over years.

FIGURE 1. Two spatial networks of long term climate data for the average period of 1980 – 2014. (Data source: ISCW-ARC.)

This article uses two spatial networks of long term climate data for the average period of 1980 – 2014, see Figure 1 above.

The data clearly highlighted: a general warming trend within the extent of the Western Cape over the last 30 years, regions and months responding differently.

The results showed significant differences in the warming and cooling over decades (10 years), half decades (five years), years, regions and months. There was a significant climatic trend of warming for the 30-year period, with a similar trend across the different wine regions of South Africa. Over all temperature elements, there was a warming trend from 1984 – 2015, maximum temperatures showed the most increase of between 1 – 2°C and minimum temperature increases were observed over all the regions, but with less intensity (<0.6°C). Temperatures in the Western Cape are projected to increase by as much as 1.5°C along the coast and 3°C inland by 2050. Rainfall was not well explained by specific long term trends, but regional and monthly changes of annual increases and decreases over decades, with a general trend of rainfall shifting more into the summer season of the Western Cape.

The 30-year long term temperature and rainfall averages for each wine producing region is described in Table 1, highlighting the cooler and warmer production areas. Figure 2 highlights the climate change impacts on the different wine producing regions considering temperature and rainfall only. The topography and distance from the ocean seemed to drive regional shifts over the three decades (1984 – 2015), with a more pronounced effect on temperature in the coastal region, some regions being more prone to change, emphasising the need for finer scale demarcation when climate aspects are considered. The analysis highlights the need for regional and monthly review in the context of climate change to be focused on maximum and minimum temperature, as when averages are used, the meaning of the data is masked. Figure 2 explains what has happened in the different wine producing regions the last 10 years compared to the long term mean.

For example the Breede River Valley is seeing increases in maximum temperatures and decreases in minimum temperatures, this could mean that the region could expect more heatwaves or higher summer temperatures along with cooler winters/spring temperatures that could manifest in the form of frost. The incidence of frost has increased in some areas within the Breede River Valley the past few seasons, having a significant impact on the crop load at harvest. The increases in rainfall in the Breede River Valley could have positive or negative impacts, very much dependant on the timing of rainfall. Figure 2 can be used to aid decision making in the context of a changing climate, some regions more prone to increased/decreased temperatures and other more prone to changes in rainfall, this knowledge could aid viticulture management strategies.

FIGURE 2. Average climate change over 30 years for each wine producing region.

Climatic indices used to summate the seasonal growing temperatures have showed significant increases. This trend is continuing and is shifting the climate zone demarcations for viticulture. However, in the context of climate change, seasonal summations are not enough to quantify the impact of temperature shifts on the grapevine. A higher temporal resolution of weather conditions are required, and highlight that the seasonal summations are driven by warmer than normal months later in the season, specifically driven by increases in temperatures in the months of December, January and March (Figure 3). The growing season is warming and demarcated areas linked to specific production and cultivar targets need to be reviewed.

Monthly temperature shifts, rather than regional temperatures better illustrated the fluctuations of temperatures across the decades. The most significant shift to warmer temperatures was noted in December, January and March, with increasing rainfall in January and March, insights that could affect the grapevine’s growth and especially ripening. Cooler minimum temperatures in September could affect budburst and the cooling temperatures in November, along with more rainfall in October/November, could delay phenology, or promote vegetative growth of the grapevine, increasing vigour. Winter months are key for chill unit calculations and efficient budburst for an even and timeous start to the growing season. April, May and July showed increasing maximum temperatures and decreasing minimum temperatures. Rainfall is decreasing overall in the winter months with the exception of increases in June for the last decade. The shifts of rainfall out of the post-harvest and winter periods, could have an impact on the soil moisture and temperature profile, this would impact the traditional irrigation strategies.

FIGURE 3. Normalised temperature and rainfall differences for months of the year for the extent of the Western Cape.

The results highlighted that the climate in the Western Cape wine growing area is changing, with a general trend of warming that was more pronounced in some regions and for some months. South Africa’s wine grape growing regions are characterised by diversity in climate, topography, soil type, etcetera. This diversity is a key for effective adaptive strategies, it allows for more complexity in the management of climate change. Changes in the areas of suitability for certain cultivars could be of major importance for the regional economy. Adaptation, change in production practices and development of new wine regions are the keys to surviving climate change. The South African wine industry has already shown considerable flexibility in shifting geographically to new production areas that are characterised by cooler climatic conditions, but this may come at a cost with regard to less favourable conditions, such as more summer rainfall, changes in wind during critical growth and ripening stages.

The study emphasised the need for more climate monitoring sites, especially in the complex terrain of the Western Cape. Spatial and temporal data sources need to be integrated to create new spatial and temporal layers of higher resolution, which could aid in more insightful within-season decision making and adaptive strategies for a warmer (or cooler) future. Future work includes the integration of climate maps in the context of grapevine modelling along with a spatial view of the seasonal shifts (www.terraclim.co.za) for improved management and adaptation.

Abstract

In the context of climate change, factors such as seasonal variability and limitations of available water resources, have increased pressures on the production of table wines, and could continue to do so without effective adaptive strategies. Almost every response of the grapevine is affected by climate, it has been scientifically shown that grapevine growth tempo, as well as final shoot length, are linked to seasonal variability and water constraints. Viticulture actions amidst the increased seasonal variable is forcing us to be more on the seasonal weather pattern pulse. When processing long term climate change in the Western Cape, it was clearly highlighted that our climate is warming in maximum temperatures and cooling in minimum temperatures. The data highlighted that months and regions within the Western Cape are responding differently within the reality of climate change. Understanding the seasonal patterns for specific regions and months within that region is important to aid effective adaption in the context of climate change.

– For more information, contact Tara Southey at tara@sun.ac.za.

 

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