PROBABILITY DISTRIBUTION FUNCTIONS APPLIED IN THE WATER REQUIREMENT ESTIMATES IN IRRIGATION PROJECTS

ABSTRACT Spain contains a third the entire irrigated area of Europe, accounting for 15% of the cultivated area of the country and almost 60% of the national agricultural production. Knowledge of the spatial and temporal variability of reference evapotranspiration (ETo) and the probabilistic theory of extreme events is crucial for the elaboration of sustainable irrigation projects. The objective of this work was to define the frequency distribution that best describes ETo for the design of irrigation systems in the region of Andalusia. We used ETo data for the period 2001 to 2015 from 56 meteorological stations. The values were accumulated over three consecutive days. For all accumulated periods, nine probability distributions were adjusted. The probability distribution that best described ETo for the design of irrigation systems in the region was the Gumbel II distribution. The maximum daily ETo to be considered in irrigation projects in this region is, on average, 10 mm. The accumulated ETo for periods of 5, 10, and 30 days that should be considered are, on average, 42 mm, 78, mm and 224 mm, respectively.

摘要：西班牙的灌溉面积占欧洲全境的三分之一，占本国耕地面积的15%，同时贡献了全国近60%的农业产值。参考作物蒸散量（reference evapotranspiration, ETo）的时空变异性与极端事件概率理论，对可持续灌溉规划的拟订至关重要。本研究旨在明确最适用于安达卢西亚地区灌溉系统设计的ETo最优频率分布模型。我们采用了2001至2015年间56个气象站点的ETo数据，将观测值按连续三日进行累积。针对所有累积时段，共拟合了9种概率分布模型。最终确定最适配该地区灌溉系统设计需求的ETo概率分布为耿贝尔Ⅱ型（Gumbel II）分布。该地区灌溉工程设计中需考量的最大单日ETo平均值为10毫米；对应5日、10日与30日累积时段的设计用累积ETo平均值分别为42毫米、78毫米与224毫米。