合肥市干旱识别及基于Copula的特征值重现期分析

Identification of Drought in Hefei City and Analysis of Return Periods of Their Characteristics Based on Copula

以合肥市月降水量为干旱指标,以轻旱等级的上下限值为干旱发生阈值,并以月水面蒸发量与土壤耕作层有效含水率之和为干旱解除阈值,采用三阈值游程理论法识别干旱,以干旱烈度和峰值强度为干旱事件的特征值,利用适于描述具有上尾相关性的GH Copula函数构建特征值的联合分布,计算干旱事件特征值的各种重现期,辨析各种重现期的内涵及其对实际旱情的反映。结果表明,基于月降水量和月水面蒸发量识别的干旱能较准确地反映实际旱情;合肥市干旱始于10、7月的可能性最高,严重干旱绝大多数均始于或包含7月;发生于2019年7~12月的干旱烈度、峰值强度的重现期分别为27.4、42.9年,烈度和峰值强度的"AND"、"OR"联合重现期分别为48.0、25.7年;联合重现期越大的干旱不代表其对承灾体造成的损失越严重。

The monthly precipitation anomaly(Pa)in Hefei City was selected as drought index,and the upper and lower limit of Pafor light drought were adopted as thresholds of drought occurrence,while the sum of monthly amount of pan evaporation and available soil water content of plow layer were adopted as threshold of drought relief.Then run theory method with three thresholds was used to identify drought events.Drought severity and peak intensity were taken as characteristic values,the GH Copula,which is suitable to reflect the positive upper tail dependence between drought characteristic variables,was used to construct the joint distribution of characteristic values.Then several return periods of identified drought events were calculated,the actual drought situations were compared with the return periods of the corresponding drought events.The results show that the identified drought events in Hefei during 1953-2019 are in good agreement with actual drought situations.Droughts are more likely to begin in October or July in Hefei,and severe drought events almost occurred beginning in July or covering July.A severe drought event occurred during July through December2019 in Hefei,return periods of drought severity and peak intensity of the drought event are 27.4 and 42.9 years respectively,while the corresponding"AND"and"OR"joint return periods are 48.0 and 25.7 years respectively.Furthermore,it doesn’t mean that hazard bearing body will suffer heavier losses from drought events with longer joint return periods.