Rainfall seasonality and timing are key climatic features affecting crop yield in rainfed agriculture (RFA). We evaluated the dynamics of temporal rainfall attributes – the strength of seasonality, the date of onset, cessation, and duration of the rainy season – over RFA areas across Ethiopia for the period 1981-2010 and explored their impacts on cereal crop production (including maize, teff, sorghum, wheat, barley, millet, oats and rice) between 1995 and 2010. First, we quantified the rainfall seasonality using an entropy-based seasonality index, defined the onset and cessation dates of rainy seasons, computed the rainy season duration, and analyzed their interannual variability and trends. Second, we correlated de-trended total cereal production during the Meher (i.e., long rainy) season (April to September) with the anomalies of the temporal rainfall attributes, and we used a univariate linear regression model to estimate the influence of changes in these attributes on crop production. We show that RFA areas in northern Ethiopia are characterized by a highly seasonal and unimodal rainfall regime. The southern parts of the RFA areas are characterized by less seasonal rainfall of bimodal and erratic nature. Cereal crop production during the Meher season, especially in teff and maize-dominated regions, is found to be correlated to both the onset (median ρ=-0.32 and -0.37, respectively) and duration (ρ=0.34 and 0.19) of the rainy season in the unimodal rainfall regime, whereas it is correlated with the rainfall seasonality (ρ=0.21) in regions with a bimodal rainfall. We estimate that on average over RFA areas, a late-onset and shorter rainy season lead to ∼1.5% and 1.1% crop production losses per pentad (5-day period), respectively.

降雨季节性和时间是影响雨养农业 (RFA) 作物产量的关键气候特征。我们评估了 1981-2010 年埃塞俄比亚 RFA 地区的时间降雨属性动态——季节性强度、雨季的开始日期、结束日期和持续时间——并探讨了它们对谷类作物生产（包括玉米、画眉草、高粱、小麦、大麦、小米、燕麦和大米）在 1995 年至 2010 年之间。首先，我们使用基于熵的季节性指数量化降雨季节性，定义雨季的开始和停止日期，计算雨季持续时间，并分析了它们的年际变化和趋势。其次，我们关联了 Meher 期间非趋势的谷物总产量（即，长雨）季节（4-9月）具有时间降雨属性的异常，我们使用单变量线性回归模型来估计这些属性变化对作物生产的影响。我们表明埃塞俄比亚北部的 RFA 地区的特点是高度季节性和单峰降雨制度。RFA 地区南部的特点是季节性降雨量较少，具有双峰和不稳定的性质。Meher 季节的谷物作物产量，尤其是在画眉草和玉米为主的地区，被发现与雨季的开始（中值 ρ=-0.32 和 -0.37）和持续时间（ρ=0.34 和 0.19）相关。单峰降雨制度中的季节，而与双峰降雨地区的降雨季节性（ρ=0.21）相关。我们估计，平均而言，在 RFA 地区，