基于Copula函数的汉江流域水文干旱风险研究

研究汉江流域水文干旱风险及驱动因素,为区域干旱预警和水资源管理提供参考。选用1964—2016年汉江流域白河、黄家港和沙洋3个水文站逐月实测径流资料,采用标准化径流指数SRI进行水文干旱分析,基于游程理论进行干旱特征变量识别,运用Copula函数计算干旱特征变量之间的联合累积概率,分析了联合重现期和同现重现期。结果表明:(1)在1964—2016年,白河站共发生水文干旱事件54次,干旱发生频繁但旱情较轻; 黄家港和沙洋站分别发生干旱事件34,32次,发生频次相对较少但旱情较重,旱情总体呈现从上游向下游加重的趋势;(2)随着干旱特征变量值增大,联合累积概率值也增大,但增大趋势变缓;(3)两变量重现期随着单变量取值增大而增大,但在相同增幅情况下,同现重现期的增幅要明显高于联合重现期;(4)当白河站干旱历时和烈度达到最大时,水文干旱事件的联合重现期为50 a左右,同现重现期为1 600 a左右,黄家港与沙洋站呈现出与白河站大致相同的趋势;(5)人类活动是1991年以来汉江流域径流减少的主要原因,对白河和沙洋站径流变化的贡献率分别为59.6%和69.2%,是汉江流域水文干旱加重的主导因素。研究显示汉江流域下游旱情较上游重,且持续受人类活动影响,应增强变化环境下区域干旱风险应对能力。

Hydrological Drought Risk in the Hanjiang River Basin Based on Copula Function

The study on the risk and driving factors of hydrological drought in the Hanjiang River Basin can provide reference for regional drought warning and water resources management. The monthly runoff data from 1964—2016 at Baihe, Huangjiagang and Shayang stations in the Hanjiang River Basin were selected, and the standardized runoff index(SRI)was used for hydrological drought analysis. Drought characteristic variables were identified based on the run theory. The joint cumulative probability between the drought characteristic variables was calculated by using Copula function, and the joint return period and co-occurrence return period were analyzed. The results showed that:(1)from 1964 to 2016, there were 54 drought events at Baihe station, indicating that the droughts were frequent but mild; there were 34 and 32 drought events at Huangjiagang and Shayang stations, respectively, indicating that the droughts were relatively less frequent but more severe; the drought situation in the Hanjiang River Basin showed an aggravating trend from upstream to downstream;(2)with the increase of the value of drought characteristic variables, the joint cumulative probability value also increased, but the increasing trend was slow;(3)the bivariate return period increased with the increase of univariate return period, but the increase of co-occurrence return period was significantly higher than that of joint return period under the same increase condition;(4)at Baihe station, when the drought duration and severity reached the maximum, the joint return period of the drought event was approximately 50 years, and the co-occurrence return period was about 1600 years; the same phenomena were found at Huangjiagang and Shayang stations;(5)human activities have been the main cause for runoff reduction in the Hanjiang River Basin since 1991, contributing 59.6% and 69.2% to runoff change at Baihe and Shayang stations, respectively, indicating that they are the dominant factors for the aggravation of hydrological drought in this basin. The results show that the droughts in the lower reaches of the Hanjiang River Basin are heavier than those in the upper reaches and are continuously affected by human activities. Therefore, the ability to cope with regional drought risk should be enhanced under the changing environment.