Calculation method of agricultural drought loss risk curve under the actual drought resistance ability condition in Southern China
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.
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