丹江口水库蓄水前后汉江中游水文干旱演变特征分析

Evolution Characteristics of Hydrological Drought in the Middle Reaches of Hanjiang River Before and After the Impoundment of the Danjiangkou Reservoir

开展水库径流调节作用下水文干旱演变研究对于干旱监测和水资源管理具有重要意义。利用1956~2020年汉江中游黄家港和皇庄2个水文站逐月实测径流资料,选用标准化径流指数(SRI)对丹江口水库运行前后水文干旱演变特征进行分析,基于Copula函数评估水文干旱特征变量联合概率和重现期的变化。结果表明:(1)与丹江口水库蓄水前相比,蓄水后2个站冬季旱情明显趋缓,而夏秋季干旱略有加重,其中黄家港站表现尤为明显;(2)蓄水后黄家港站轻旱事件的发生频率明显增加,而皇庄站轻旱略有增加,但2个站的中、重和特旱事件发生频率均显著减少;(3)就干旱历时和烈度平均值而言,蓄水后黄家港站有所增加,皇庄站则略有减少。从烈度峰值平均值来看,蓄水后2个站均有不同程度的降低;(4)在给定某一重现期下,蓄水后2个站干旱特征变量的联合重现期总体呈现增加趋势,而同现重现期整体表现为下降趋势;(5)在来水偏枯年份,丹江口水库加大下泄流量可一定程度上缓解汉江中下游冬春季旱情,但汛末蓄水减少了下游河道径流量,则有可能会加重旱情。

It is of great significance for drought monitoring and water resources management to study the evolution of hydrological drought under the effect of reservoir runoff regulation.Based on the monthly measured runoff data from 1956 to 2020 at Huangjiagang and Huangzhuang stations in the middle reaches of Hanjiang River,the standardized runoff index(SRI)was used to analyse the hydrological drought changes before and after the Danjiangkou(DJK)Reservoir impoundment.The variations of joint probability and return period of hydrological drought characteristic variables were evaluated based on Copula function.Results indicated that:(1)Compared with that before the DJK Reservoir impoundment,the drought situations in winter at the two hydrological stations after operation of the DJK Reservoir were significantly reduced,while the drought conditions in summer and autumn were slightly aggravated,especially at Huangjiagang station;(2)After the impoundment of the DJK Reservoir,the frequency of light drought events at Huangjiagang station increased significantly,and that in Huangzhuang station increased slightly,while the frequency of moderate,severe and extreme drought events at the two hydrological stations decreased significantly;(3)As for the average value of drought duration and severity,Huangjiagang station increased and Huangzhuang station decreased slightly after operation of the DJK Reservoir.From the average value of drought peak,the two hydrological stations decreased in varying degrees after impoundment of the DJK Reservoir;(4)Given a certain return period,the joint return period of drought characteristic variables of the two hydrological stations after impoundment showed an increasing trend,while the co-occurrence return period exhibited a downward trend as a whole;(5)In dry years,increasing the outflow of the DJK Reservoir can alleviate winter and spring drought conditions in the middle-lower reaches of Hanjiang River to some extent,but the impoundment of the reservoir at the end of the flood season reduces the streamflow of the downstream river,which may aggravate the drought condition.