2015—2017年南非西开普省干旱事件的时空特征分析

Spatial and Temporal Characterization of the Urban Drought in the Western Cape,South Africa,from 2015 to 2017

2015—2017年南非西开普省遭受了特大干旱冲击,造成了城市可用水资源的极度短缺,使其首都开普敦市成为人类历史上首个面临“零日”灾难(关闭该城市水龙头的确切时间)威胁的现代城市。但此次灾害的多种致灾因素的交互机理和过程尚不明确,人为供用水管理如何科学应对自然降水变异的模式有待进一步挖掘。因此,通过气象干旱、水文干旱和城市供用水管理3个维度挖掘其中的关键阶段、空间分布和管理效益。结果表明:(1)西开普省2015—2017年气象干旱面积和强度显著增加,且2017年5月干旱情况最为严重。相比于标准化降水指数,标准化降水蒸散指数检测到的干旱更为显著。(2)西开普省的水文干旱在2017年5月最为严重,这与气象干旱的时空特征规律大体一致,体现出气象—水文干旱迅速传播的特征。标准化径流指数结果与水库储水量变化均反映该地区的水资源缺乏,表明此次干旱事件对严重依赖降雨和水库供水的西开普省产生了显著影响。(3)西开普省政府针对此次干旱演进过程采取了不同等级的用水限制和管理政策,有效推迟和避免了“零日”灾难,但在政治和经济等方面解决用水不平等的问题还值得商榷和改良。研究表明城市干旱问题涉及气象、水文和供用水多个系统及其相互作用,需要从致灾时空过程角度监测、理解和减缓。

From 2015 to 2017,the Western Cape province in South Africa suffered a severe drought,resulting in an extreme shortage of water resources in the city,making its capital,Cape Town,the first modern city in human history to face the threat of a“Day Zero”disaster(i.e.,the day when the city’s water taps are turned off).However,the interaction mechanisms and processes of various disaster-causing factors remain unclear,and how to scientifically cope with the natural precipitation variation mode by man-made water-supply management needs to be further explored.Therefore,this paper explores the key stages,spatial distribution,and management benefits from the three dimensions of meteorological drought,hydrological drought,and urban water supply management.The results show the following:①The Western Cape experienced a significant increase in the area and intensity of meteorological drought from 2015 to 2017,with the most severe drought conditions occurring in May 2017.Compared with the Standardized Precipitation Index(SPI),the drought detected by Standardized Precipitation Evapotranspiration Index(SPEI)was more significant.②The hydrological drought conditions in the Western Cape in May 2017 were the most severe.This is broadly consistent with the pattern of spatial and temporal characteristics of meteorological drought,reflecting the rapid spread of meteorological-hydrological drought.Both the Standardized Runoff Index(SRI)results and the change in reservoir water volume reflect water scarcity in the region,indicating that the drought event had a serious impact on the Western Cape,which relies heavily on rainfall and reservoir water supply.③The Western Cape government adopted different levels of water restrictions and management policies in response to the evolution of this drought,effectively delaying and avoiding a“Day Zero”disaster;however,addressing the political and economic aspects of water inequality is still debatable and worth improving.This paper shows that urban drought problems involve multiple systems and interactions among the meteorology,hydrology,and water supply,and need to be monitored,understood,and mitigated in terms of the spatial and temporal processes.