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基于前期研究提出的4种假定灌溉条件下季节性干旱频率-旱灾损失率定量关系曲线,针对不同频率干旱发生时来水条件存在的差异与实际抗旱能力的不同,研究在变化的实际抗旱能力下,农业季节性干旱频率和旱灾损失率之间的定量关系,以此计算出实际抗旱能力下农业旱灾损失风险曲线。首先,以干旱期间供水满足需水的比例作为抗旱能力指标,分别建立抗旱能力指标-来水频率、干旱频率-干旱烈度保证率之间的关系曲线,以干旱烈度保证频率表征来水频率,进而得出各次干旱过程的抗旱能力指标与干旱频率的一一对应关系。然后,利用Copula函数计算干旱频率,通过EPIC模型模拟水稻产量并计算损失,建立干旱频率-假定灌溉水平-旱灾损失率三者间关系。最后,根据抗旱能力和干旱频率的对应关系,并以抗旱能力指标反映灌溉水平,可推得现状水平年实际抗旱能力下的干旱频率-旱灾损失率曲线。在湖南株洲市水稻旱灾损失风险计算的应用实例表明,实际抗旱能力下双季早稻夏季5—7月干旱频率-旱灾损失率之间,基本呈半对数函数趋势关系。对比历史旱灾损失调查结果,当发生2、5、10年一遇的干旱时,旱灾损失率的实际调查结果与理论计算值的相对差值分别为1.69%、-5.33%和-4.81%。
Based on the quantitative relationship curves of seasonal drought frequency and drought loss rate under the four kinds of assumed irrigation conditions put forward in the previous study, according to the difference of water supply conditions at different frequencies of drought and actual drought resistance ability, , Agricultural seasonal drought frequency and drought loss rate in order to calculate the actual drought-resistant agricultural drought loss risk curve. First, taking the ratio of water demand to water demand during drought period as the indicator of drought resistance, the relationship curves of drought resistance index, water frequency, drought frequency and drought intensity guarantee rate are respectively established, and the water frequency is characterized by drought intensity guarantee frequency Draw a one-to-one correspondence between drought resistance index and drought frequency of each drought process. Then, using the Copula function to calculate the frequency of drought, simulating the rice yield and calculating the loss through the EPIC model, establishing the relationship between drought frequency - assumed irrigation level - drought loss rate. Finally, according to the correspondence between drought tolerance and drought frequency, and reflecting the irrigation level with drought resistance index, we can deduce the drought frequency-drought loss curve under the actual level of drought resistance. The application example of calculating the risk of rice drought loss in Zhuzhou, Hunan shows that under the actual drought resistance capacity, the drought frequency and drought loss rate in May-July in summer are basically semi-logarithmic trend. Compared with the results of historical drought loss survey, the relative differences between the actual survey results and the theoretical values of drought loss rates of 2.5, 10 and 10 years respectively are 1.69%, 5.33% and -4.81% respectively.