A revision of the Combined Drought Indicator (CDI) used in the European Drought Observatory (EDO)

摘要

Building on almost 10?years of expertise and operational application of theCombined Drought Indicator (CDI), which is implemented within the EuropeanCommission's European Drought Observatory (EDO) for the purposes of earlywarning and monitoring of agricultural droughts in Europe, this paperproposes a revised version of the index. The CDI conceptualizes drought as acascade process, where a precipitation shortage (WATCH stage) develops intoa soil water deficit (WARNING stage), which in turn leads to stress forvegetation (ALERT stage). The main goal of the revised CDI proposed here isto improve the indicator's performance for those events that are currentlynot reliably represented, without altering either the modelling conceptualframework or the required input datasets. This is achieved by means of twomain modifications: (a) use of the previously occurring CDI value to improvethe temporal consistency of the time series and (b) introduction of twotemporary classes – namely TEMPORARY RECOVERY for soil moisture andvegetation greenness, respectively – to avoid brief discontinuities in astage. The efficacy of the modifications is tested by comparing theperformances of the revised and currently implemented versions of theindicator for actual drought events in Europe during the last 20?years. Therevised CDI reliably reproduces the evolution of major droughts,outperforming the current version of the indicator, especially forlong-lasting events, and reducing the overall temporal inconsistencies instage sequencing of about 70?%. Since the revised CDI does not needsupplementary input datasets, it is suitable for operational implementationwithin the EDO drought monitoring system.