Steyn, A. S.Coetzer, G. M.Tharaga, Phumudzo Charles2016-01-072016-01-072014-12http://hdl.handle.net/11660/2049English: Climate is an important aspect of crop production, determining the suitability of a given region to deciduous fruit production and largely controls the yield and quality thereof. Climate has always been variable, but there is strong evidence of global and regional-scale climate change since the advent of the industrial era. In South Africa mean surface temperatures have revealed an increasing trend over the last century. South Africa is renowned for its quality export fruit, but deciduous fruit production is already marginal under current conditions. Problems related to climate change will add strain to fruit growers and impact directly on livelihoods within the main production regions. It takes a considerable time to establish fruit orchards, thus it is even more important for these producers to take climate change in consideration. Since deciduous fruits require winter chilling to break dormancy, the main objective of this study was to determine the effect of climate change on accumulated chill units at three sites in South Africa, namely Bethlehem, Ceres and Upington. Observed winter temperature data were obtained for the base period 1981 – 2010, while projected temperatures up to 2100 were acquired from a Global Climate Model (GCM). Hourly temperatures were derived from these daily minimum and maximum temperatures by means of a Temporal Downscaling Model. The Utah Model and the Daily Positive Utah Chill Unit Model were used to quantify winter chill, accumulated over each winter season from 1981 – 2100. Cumulative distribution functions were used to identify shifts in industry related thresholds for accumulated positive chill units (PCUs). The results indicated that the impacts of climate change vary among regions. Historical accumulated PCUs showed no significant trend for Bethlehem, but a decreasing trend for both Ceres and Upington. The GCM projections indicated a continuation of these trends over the course of the 21st century, thus resulting in an increase in deficient winter chill problems in Ceres and Upington in future. Potential adaptations involve cultivar and/or rootstock selection, microclimate manipulation and the use of chemical rest-breaking agents.Afrikaans: Klimaat is ʼn belangrike aspek van gewasproduksie en bepaal die geskiktheid van 'n gegewe streek vir die produksie van sagtevrugte en beheer grootliks ook die opbrengs en kwaliteit daarvan. Klimaat is nog altyd veranderlik, maar daar is sterk bewyse van globale en plaaslike-skaal klimaatsverandering sedert die aanvang van die industriële era. In Suid-Afrika toon gemiddelde oppervlaktemperature 'n warm tendens oor die afgelope eeu. Suid-Afrika is bekend vir sy kwaliteit uitvoervrugte, maar met sagtevrugte produksie reeds marginaal onder die huidige toestande, sal probleme weens klimaatsverandering meer druk op vrugteprodusente plaas en die lewensbestaan binne die hoofproduksiestreke beïnvloed. Dit neem 'n geruime tyd om sagtevrugteboorde te vestig, dus is dit selfs belangriker vir dié produsente om klimaatsverandering in ag te neem. Omrede sagtevrugte winterkoue benodig om rus te breek, was die hoof doel van hierdie studie om die effek van klimaatsverandering op geakkumuleerde koue-eenhede te bepaal by drie streke in Suid-Afrika, naamlik Bethlehem, Ceres en Upington. Waargenome wintertemperatuurdata is verkry vir die basisperiode 1981 – 2010, terwyl geprojekteerde temperature tot 2100 bekom is van 'n Globale Klimaatmodel (GKM). 'n Temporale Afskalingsmodel is gebruik om uurlikse temperature af te lei van hierdie daaglikse minimum en maksimum temperature. Die Utah Model en die Daaglikse Positiewe Utah Koue Eenheid Model is gebruik om winterkoue te bepaal, geakkumuleer oor elke winterseisoen van 1981 – 2100. Kumulatiewe verspreidingsfunksies is gebruik om verskuiwings in industrie-verwante drempels vir geakkumuleerde positiewe koue eenhede (PKE) te identifiseer. Die resultate dui dat die impak van klimaatsverandering wissel tussen streke. Historiese geakkumuleerde PKE het geen betekenisvolle tendens vir Bethlehem getoon nie, maar dalende neigings vir beide Ceres en Upington. Die GKM-projeksies toon 'n voortsetting van hierdie tendense deur die 21ste eeu, wat dui op 'n toename in probleme met gebrekkige winterkoue in Ceres en Upington in die toekoms. Potensiële aanpassings behels kultivar- en/of onderstamkeuse, mikroklimaat-manipulasie en die gebruik van chemiese rusbrekingsmiddels.enAdaptation strategiesDeciduous fruitTemporal downscaling modelFruitCrops and climateFruit -- Climatic factorsDissertation (M.Sc.Agric. (Soil, Crop and Climate Sciences))--University of the Free State, 2014DissertationUniversity of the Free State