Rainfall (RF) variability has been suggested as the primary reason for low paddy production in the recent past under minor irrigation tanks (MITs). A study was conducted to verify the relationship between observed crop success/failures and the RF variability in the Bayawa MIT system in the Kurunegala district of Sri Lanka. Seasonal and annual RF variability and its effect on paddy crops were analyzed. Daily rainfall data were obtained from the Wariyapola station from 1983 to 2014. Paddy production data for 20 consecutive seasons from 2003 to 2014 were collected from the Department of Census and Statistics (DCS), Colombo. Paddy samples from the Bayawa command area were used to calculate the land productivity and compared between the two cultivation seasons. Three types of direct RF impacts on paddy production in the Bayawa MIT system were identified: (1) reductions in the cropping intensity (CI), (2) total crop failures and (3) reductions in yield. During the study period, the CI was 80–173% with an average of 140% (expected value is 200%). Sixty percent of annual and seasonal RF values were below the long-term average showing a direct effect of RF on crop failures. Low production is not only due to the variability of annual or seasonal RF during the cultivation seasons, but also due to poor water management decisions, such as not cultivating considering the available water in the MIT. Thus, there is a need for wise water management decisions of MITs in this study area based on the variability of RF for sustainable paddy production.

中文翻译：

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降雨变化对稻田生产的影响：以斯里兰卡巴瓦瓦小灌池为例

有人提出降雨（RF）的可变性是近来在小型灌溉水箱（MIT）下水稻产量低的主要原因。进行了一项研究，以验证观察到的作物成功/失败与斯里兰卡Kurunegala地区的Bayawa MIT系统中RF变异之间的关系。分析了季节性和年度RF变异性及其对稻谷作物的影响。每日降雨量数据是从1983年至2014年从Wariyapola站获得的。2003年至2014年连续20个季节的稻谷生产数据是从科伦坡的政府统计局（DCS）收集的。来自Bayawa的水稻样品命令区域用于计算土地生产力，并在两个耕种季节之间进行比较。三种直接射频对巴瓦瓦稻谷生产的影响确定了MIT系统：（1）降低种植强度（CI），（2）作物总歉收和（3）降低产量。在研究期间，CI为80–173％，平均为140％（预期值为200％）。年度和季节性RF值的60％低于长期平均值，表明RF对作物歉收的直接影响。产量低下不仅是由于耕种季节中年度或季节RF的变化，还归因于不良的水管理决策，例如不考虑MIT的可用水进行耕种。因此，在该研究领域中，有必要基于可持续水稻生产的RF变异性，对MIT进行明智的水管理决策。