Drought is one of the most severe natural disasters with a high risk for human livelihoods. Remote sensing based drought indices can identify dry periods using, e.g., precipitation or vegetation information. Besides frequency, duration, and intensity, the timing of a drought onset and duration are important variables to measure the drought impact and risk. This article classifies drought events based on the timing of the drought and with regard to their impact on vegetation production during different crop growing stages. Drought and nondrought seasons are analyzed in Eastern Cape Province, South Africa. Here, the impact of a drought on vegetation production highly depends on the starting point and the duration of rainfall during the growing season. Weighted linear combination was applied based on vulnerable vegetation growing stages in the phenology to classify drought severity per season. Particularly the extreme drought season in 2015/2016 as well as the normal nondrought season in 2011/2012 was emphasized. The developed approach serves as input to quantify drought impact per cropping season from local to regional scales. Integration of socio-economic information can further complement this hazard information to support the quantification of the actual drought risk.

中文翻译：

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时间就是一切——用于风险评估的干旱分类

干旱是最严重的自然灾害之一，对人类生计的风险很高。基于遥感的干旱指数可以使用例如降水或植被信息识别干旱期。除了频率、持续时间和强度之外，干旱发生的时间和持续时间也是衡量干旱影响和风险的重要变量。本文根据干旱发生的时间以及它们在不同作物生长阶段对植被生产的影响对干旱事件进行了分类。分析了南非东开普省的干旱和非干旱季节。在这里，干旱对植被生产的影响在很大程度上取决于生长季节降雨的起点和持续时间。基于物候中脆弱的植被生长阶段应用加权线性组合来对每个季节的干旱严重程度进行分类。特别强调了 2015/2016 年的极端干旱季节以及 2011/2012 年的正常非干旱季节。所开发的方法可作为输入，以量化从地方到区域尺度的每个作物季节的干旱影响。社会经济信息的整合可以进一步补充这一灾害信息，以支持实际干旱风险的量化。