基于干旱和水位特征构建水库人工增雨需求指数

Construction of artificial precipitation demand level index of the reservoir based on drought and water level characteristics

为定量化描述水库人工增雨需求,以浙江兰溪芝堰水库为研究对象,基于降水、径流和水位历史观测数据,采用实际概率分布阈值法确定逐月不同等级水库水位指标(Water Level Index, WLI)百分位阈值,通过熵权法联合表征气象干旱的标准化降水指数(Standardized Precipitation Index, SPI)和表征水文干旱的标准化径流指数(StandardizedStreamflow Index,SSI)构建水库整体干旱指数(Drought Index, DI),综合WLI和DI构建水库人工增雨需求指数(Demand Level Index, DLI)等级,研究WLI、DI和DLI时间特征,结合水库历史记录分析DLI的适用性,结果表明:(1)确定的逐月不同等级WLI百分位阈值能够精细化表征水库在一年内不同时期的缺水程度。(2)1990—2019年气象干旱无明显变化,水文干旱程度加大,其中春季变旱趋势最明显。(3)气象(水文)干旱在夏秋季发生总频率为33.9%(35.0%),高于冬春两季的30.0%(28.3%)。重、特旱在春季的发生频率最高,气象和水文干旱发生频率分别为11.2%和10.0%。水文干旱与气象干旱的时滞性不明显,水文干旱平均历时和平均烈度均高于气象干旱,具有更高的危害性。(4)不同等级的DLI年际分布与WLI较为相近,季节分布与DI分布相似。与2004年之前相比,2004年之后增雨需求出现更为频繁,持续存在时间更长。增雨需求在夏季占比最高,为40.0%,但高度、强烈增雨需求在春季占比最高,为14.4%。(5)构建的DLI等级可以较好地表征水库实际需求,当DLI等级大于等于4持续多个月时,水库可能会出现用水紧张并应采取相关紧急措施。

In order to provide a quantitative method to describe artificial precipitation demand,taking Zhiyan reservoir in Lanxi as the research object,based on precipitation,runoff and water level data,the percentile threshold of monthly water level index(WLI)with different grades of the reservoir was derived from real sample probability distribution of water level,the drought index(DI)was con⁃structed by using the entropy weight method combined with the standardized precipitation index(SPI)and the standardized streamflow index(SSI),then WLI was integrated with DI to generate the demand level index(DLI)to describe artificial precipitation demand of res⁃ervoir objectively.The temporal characteristics of WLI,DI and DLI were studied,the applicability of DLI was analyzed based on the reservoir history records,the main conclusions are as follows:(1)The constructed percentile threshold of monthly WLI with different grades was able to reflect the water shortage of the reservoir precisely in different periods of a year.(2)There was no significant change in meteorological drought from 1990 to 2019,meanwhile hydrological drought showed an increasing trend,and the increasing trend was most obvious in spring.(3)The total occurrence frequency of meteorological(hydrological)drought in summer and autumn was 33.9%(35.0%),it is higher than that(30.0%(28.3%))in winter and spring.The occurrence frequency of severe and extreme drought in spring was the highest,and meteorological and hydrological drought accounted for 11.2%and 10.0%respectively in spring.Hydrological drought did not lag behind and had a more serious effect than meteorological drought.(4)The inter-annual distribution of DLI was simi⁃lar to that of WLI,and the seasonal distribution of DLI was similar to that of DI.Artificial precipitation demand appeared more fre⁃quently and last longer in the years after 2004 than before 2004.Demand occurred most frequently in summer,accounting for 40.0%,however the demand of high and very high level occurred most frequently in spring,accounting for 14.4%.(5)The integrated DLI grades could well reflect the actual demand of the reservoir,and when DLI grade was greater than or equal to 4 for several months,the reservoir might be short of water and emergency measures required to be taken.