Impacts of climate change on accumulated chill units at selected fruit production sites in South Africa

Most deciduous fruit trees require chilling temperatures above freezing to break dormancy. Chilling requirement varies between cultivars. Cultivar selection for a specific climate production region is therefore crucial for successful cultivation of such crops. Several models exist to quantify winter chill, and each production region uses a model that has been shown to perform well under local climatic conditions. Historical analysis of chill units is a necessary first step when considering potential impacts of climate change. Input data was in the form of observed hourly temperature records representing climatic conditions for 1981-2010 (historically observed) and the projected future temperatures for the periods 2011-2040, 2041-2070 and 2071-2100. Projected temperatures up to 2100 were derived from three CCAM ensemble members which were derived using lower-boundary forcing from General Circulation Models (GCMs) used in IPCC-AR4. All ensembles were for the A2 greenhouse gas emissions scenario. Changing climatic conditions in all the selected study areas are expected to adversely affect the amount of accumulated positive chill units over time and hence the productivity of deciduous fruits for the historical period of 1981-2010 for all the study areas. The significant and negative trends in accumulated winter chill have been observed across Bethlehem and Upington and are projected to continue into the near and distant future.