CLIMATE CHANGE IN THE WESTERN CAPE OF SOUTH AFRICA: TRENDS, PROJECTIONS AND IMPLICATIONS FOR CHILL UNIT ACCUMULATION

Abstract

The Western Cape region of South Africa, a major producer of deciduous fruit, has been identified as highly vulnerable to climate change. Climatic trends were analysed on a monthly basis for 12 rural meteorological stations across the region for the period 1967 to 2007. Significant warming trends were found for midto late-summer and end-winter to spring for daily minimum temperature (Tmin), and for mid-summer, autumn and spring for daily maximum temperature (Tmax). Chill unit accumulation has decreased significantly, particularly in autumn. Air temperatures are predicted to increase by a further 1-2°C within the next 30 years, together with decreasing rainfall especially in autumn/winter. An analysis of possible impacts of regional projections of climate change on deciduous fruit production was conducted, with the emphasis on chilling accumulation and dormancy in apples. The warmer or otherwise more marginal production areas, and high chill cultivars are likely to be the first to experience negative impacts of warming. INTRODUCTION Global climate change is occurring as evidenced by warming of average air and ocean temperatures, melting of snow and ice, and rising sea level (IPCC, 2007). Mediterranean-climate regions worldwide have been identified as highly vulnerable to climate change (Baldocchi and Wong, 2006), including the Western Cape region of South Africa (Midgley et al., 2005). Climate projections for fruit regions for 2030-2040 include warming by 1-2°C, reductions in frontal autumn and winter rainfall, and a contraction of the winter season (Hewitson et al., 2005). Apples are generally grown under conditions of insufficient winter chilling; this necessitates the use of chemical rest-breaking treatments to achieve satisfactory budburst, fruit set, yield, and fruit quality (Cook and Jacobs, 2000). In the event of climate warming, we expect that accumulation of chill hours will decrease, eventually reaching a critical threshold at which apple production would no longer be commercially sustainable in currently marginal areas. However, the rate of decline in chill hours could vary intra-seasonally, with different phenological results, and between colder and warmer production areas. We set out to analyze recent historical regional-scale changes in temperature and chill accumulation, predicted reductions in chill accumulation with future warming, and implications for fruit production, particularly apples. MATERIALS AND METHODS Recent Historical Temperature and Chill Unit Trends in the Western Cape Quality-controlled data for twelve meteorological stations throughout the Western Cape of South Africa (Fig. 1) were obtained from the division AgroMet of the Institute for Soil, Climate and Water, Agricultural Research Council, South Africa, for the period 1967-2007. The stations are spread throughout the climatically divergent fruit-growing regions. Daily minimum (Tmin) and maximum (Tmax) air temperatures, and monthly means of Tmin and Tmax were used. Langkloof Experimental Farm was excluded due to closure in Proc. IX IS on Orchard Systems