实际抗旱能力下的南方农业旱灾损失风险曲线计算方法

摘要

Based on the relation curve of seasonal drought frequency and drought loss proposed in previous study under four different irrigation levels, the quantitative relationship between seasonal drought frequency and drought loss has been calculated to construct the drought loss risk curve, considering the changes of actual drought resistance ability with drought frequency. First, the ratio of water supply to meet the water demand in periods of drought was defined as drought resistance index. The relation curve between drought resistance index and inflow frequency, and the relation curve between drought frequency and guaranteed rate of drought intensity were established respectively, and then using guaranteed rate of drought intensity to express inflow frequency, the one-to-one relationship between drought resistance index and drought fre-quency of each drought process was obtained. Then,drought frequency can be calculated using Copula func-tion,the crop yield was simulated and yield loss rate under drought was computed using the Environmental Policy Integrated Climate Model, and the relations were set up among drought frequency, irrigation levels and drought loss rate. At last, the drought resistance index can express irrigation levels, the relation curve can be estimated between drought frequency and drought loss rate under the actual drought resistance abili-ty conditions, which can be regarded as agricultural drought loss risk curve. By applying the above calcula-tion method in Zhuzhou City of Hunan Province, the results show that the relation curves of drought fre-quency and drought loss rate of early rice during summer from May to July under the actual drought resis-tance ability conditions basically complies with semi-logarithmic function in line with trends in the relation-ship. In comparing with the history crop yield losses of drought, when 2-year, 5-year and 10-year return droughts take place, the relative errors of the actual survey results and theoretical computation values of drought loss rate are 1.69%,-5.33% and -4.8%,respectively.%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%。