Abstract. Building on almost ten years of expertise and operational application of the Combined Drought Indicator (CDI), which is operationally implemented within the European Commission’s European Drought Observatory (EDO) for the purposes of early warning and monitoring of agricultural droughts in Europe, this paper proposes a revised version of the index. The CDI conceptualizes drought as a cascade process, where a precipitation shortage (WATCH stage) develops into a soil water deficit (WARNING stage), which in turn leads to stress for vegetation (ALERT stage). The main goal of the revised CDI proposed here, is to improve the indicator’s performance for those events that are currently not reliably represented, without drastically altering the modelling framework. This is achieved by means of two main modifications: (a) use of the previously occurring CDI value to improve the temporal consistency of the timeseries, (b) introduction of two temporary classes – namely, soil moisture and vegetation greenness – to avoid brief discontinuities in a stage. The efficacy of the modifications is tested by comparing the performances of the revised and currently implemented versions of the indicator, for actual drought events in Europe during the last 20 years. The revised CDI reliably reproduces the evolution of major droughts, out-performing the current version of the indicator, especially for long-lasting events. Since the revised CDI does not need supplementary input datasets, it is suitable for operational implementation within the EDO drought monitoring system.

中文翻译：

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作为欧洲干旱观测站（EDO）一部分的综合干旱指标（CDI）的修订版

摘要。本文基于综合干旱指标（CDI）的近十年的专业知识和业务应用，该指标已在欧洲委员会的欧洲干旱观测站（EDO）内实施，目的是预警和监测欧洲的农业干旱。索引的修订版。CDI将干旱概念化为一个级联过程，在此过程中，降水不足（WATCH阶段）发展为土壤缺水（WARNING阶段），进而导致植被压力（警报阶段）。此处提出的修订的CDI的主要目标是，在不大幅更改建模框架的情况下，针对那些当前无法可靠表示的事件，提高指标的绩效。这是通过两个主要修改来实现的：（a）使用先前出现的CDI值来改善时间序列的时间一致性，（b）引入两个临时类-土壤水分和植被绿色-避免短暂的不连续性在一个阶段。通过比较指标的修订版和当前实施版的性能，测试修改的有效性，以了解过去20年来欧洲的实际干旱事件。修订后的CDI可靠地再现了主要干旱的演变，胜过了当前版本的指标，特别是对于持久事件。由于修订后的CDI不需要补充的输入数据集，因此适合在EDO干旱监测系统内进行操作实施。