Robusta coffee is the primary source of income for millions of smallholder farmers throughout the world’s tropics. The price smallholder farmers can get for their coffee is strongly influenced by bean characteristics (i.e. beans are of a sufficient size and have minimal defects). Climate is a key determinant of successful coffee production, but scant research has been undertaken to test and quantify climate impacts on robusta coffee bean physical characteristics. Here we investigate how climate relates to the risk of poor coffee bean characteristics in one of South East Asia’s key coffee producing areas, the central highlands of Vietnam. We use 5 years (2012–2016) of coffee bean characteristic data from 60 farms. Hierarchical modelling was used to investigate how rainfall and temperature related to two indicators of coffee bean characteristics (1) the probability of below average coffee bean size and (2) the probability of above average coffee bean defects. Low rainfall (<1600 mm) during the late growing season (July-September) greatly increased the risk (>80% probability) of below average coffee bean size. Conversely, high rainfall (>750 mm) and high mean minimum temperature (>22 °C) during harvest (October-December) increased the risk (>75% probability) of above average coffee bean defects. Various coffee bean characteristic subcomponents (e.g. insect damage and mouldy beans) and different bean sizes were also examined and were affected by a range of rainfall and temperature predictors across the flowering, growing and harvest seasons. With this information targeted risk-management strategies (e.g. targeted irrigation during hot and dry growing seasons, adjusting harvest timing and employing drying techniques during wet and cold harvest periods) could be developed to minimise the effect of climate conditions that increase the risk of coffee bean defects. Successfully managing the impacts identified here, could decrease coffee bean defects and in turn increase the incomes of smallholder coffee farmers.

罗布斯塔咖啡是全世界热带地区数百万小农的主要收入来源。小农户可以以咖啡获得的价格受豆子特性的强烈影响（即豆子尺寸足够大且缺陷最少）。气候是成功生产咖啡的关键因素，但很少进行研究来测试和量化气候对罗布斯塔咖啡豆物理特性的影响。在这里，我们调查了气候如何与东南亚主要咖啡产区之一越南中部高地的咖啡豆特性差的风险相关。我们使用来自60个农场的5年（2012-2016年）咖啡豆特征数据。分层建模用于研究降雨和温度与咖啡豆特征的两个指标之间的关系：（1）咖啡豆尺寸低于平均水平的概率和（2）咖啡豆缺陷高于平均水平的概率。生长季后期（7月至9月）的低降雨量（<1600毫米）大大增加了咖啡豆低于平均大小的风险（概率大于80％）。相反，在收获期间（10月至12月），高降雨（> 750毫米）和平均最低平均温度（> 22°C）较高，会增加咖啡豆缺陷高于平均水平的风险（> 75％概率）。还检查了咖啡豆的各种特征性子成分（例如，虫害和发霉的咖啡豆）以及不同的咖啡豆大小，这些咖啡豆在开花，生长和收获季节受到一系列降雨和温度预测因素的影响。利用这些信息，可以制定有针对性的风险管理策略（例如，在炎热和干燥的生长季节进行有针对性的灌溉，在湿热和寒冷的收获期调整收获时机并采用干燥技术），以最大程度地减少增加咖啡豆风险的气候条件的影响。缺陷。成功地管理此处确定的影响，可以减少咖啡豆缺陷，进而增加小农咖啡农的收入。