基于区域农业用水量的干旱重现期计算方法

为研究实际水利条件下农业干旱的发生规律，简化农业干旱事件的评估方法，提出基于区域农业用水量的干旱重现期计算方法。通过构建农业用水量距平百分率干旱指标W_A，在基于降雨量距平百分率干旱指标P_A识别干旱事件的基础上，提取W_A干旱指标下的干旱历时和干旱烈度特征变量，并根据以P_A为干旱指标的干旱烈度频率分布曲线F_S（x）和干旱历时频率分布曲线F_D（x），运用Copula的简化方法计算基于W_A的干旱事件重现期T，最后结合基于P_A的干旱事件重现期T₀，回归分析出T与T₀间关系的计算公式。选取干旱灾害影响严重的亳州市为实证区域开展应用研究，计算得到1975-2007年各场干旱事件的T₀和T以及T₀与T的经验关系式。结果表明:T比T₀更合理地反映区域农业实际受旱状况，重现期T₀和T间存在高度的相关关系，采用T的回归方程可简化计算考虑区域实际抗旱能力下的干旱事件重现期，在区域防旱减灾实践中具有推广应用价值。

Computational methods of drought return periods based on the regional agricultural water consumption

In order to research the appearance of agricultural drought under the actual water projects, the computational method for the return periods of drought events, based on the regional agricultural water consumption, is presented in this study. Through the drought index establishment of the anomalous percentages of agricultural water consumption(W_A), on the basis of drought events recognized by the drought index P_A of precipitation anomalous percentages, the drought characteristic variable of the severity and duration for drought events based on W_A were extracted. Meanwhile, according to the frequency distribution curves F_S(x) of drought severity and the frequency distribution curves F_D(x) of drought duration obtained with P_A as the drought index, the return periods T of drought events based on W_A were computed by use of the simplified method of Copula. Finally, combined with the return periods T₀ of drought events based on P_A, the formula of relationship between T and T₀ was obtained through the analysis of regression. The method was applied into Bozhou city as the exemplary region for the severest influence from the drought, and the empirical relation between T and T₀ was built as per all the drought events from 1975 to 2007. The results indicate:compared with T₀, the severity of drought events judged by T is more consistent with the reality; there is an essential correlation between T₀ and T, and the regression equation of T can be accepted as the simple estimation formula of return periods T of drought events when it comes to actual drought resistance ability of one region, and is valuable for popularized application in the process of drought mitigation and loss reduction of one region.