Drought indicators in The Netherlands

Abstract

In 2018 The Netherlands experienced the most severe drought since 1976. In response to this, the Minister of Infrastructure and Water Management established the 'Beleidstafel Droogte'. An external scientific committee took part in the Beleidstafel Droogte. One of their key recommendations was to introduce other drought indicators since the currently used indicator (precipitation deficit) is not sufficient due to limitations. This research investigates what drought indicators can be used in The Netherlands to support anticipative drought management. For water managers, it is crucial to know when and where drought occurs, and how severe this drought is. To reveal the start, severity, and ending of a drought, drought indicators can be used. However, to define drought, regional differences need to be incorporated. Therefore, this research used a case study area to find out what drought indicators can be introduced. Within the boundaries of this area, three different analyses were conducted: 1) hydrological analysis, 2) stakeholder analysis and 3) policy analysis. According to the results, a set of potentially relevant and suitable drought indicators was selected. These drought indicators were tested with focus groups to determine whether they can be used to support anticipative drought management. The area of water board Vallei & Veluwe was selected as the case study area. Concerning the hydrological analysis, multiple methods were applied to obtain a better understanding of the water system and essential hydrological processes. Because of the relative nature of drought, several stakeholders that are directly affected by drought were interviewed. Through semi-structured interviews, information concerning drought was obtained about the stakes and information needs for different stakeholders. Since measures can be taken to anticipate drought or to mitigate drought problems, the policy on drought was considered. In this way, the interrelation between policy on drought and drought indicators was taken into account. The results of the analyses mentioned above led to the following selection of drought indicators: SPI-1 & SPI-3, soil moisture, stream discharge, groundwater levels/isohypse, NDVI and EVI. To test the selected indicators can support anticipative drought management, two focus groups session were organised. For these focus groups, a dry year was reconstructed, which was explored by the participants. Based on the information that was presented to the participants, they were asked whether they would advise taking measures and what their level of alertness was. One group received information from the selected indicators, whereas the other group received information which is used nowadays for drought monitoring. After evaluating and comparing the focus groups, conclusions were drawn. The participants that received information from the selected drought indicators acted more pro-active, because: 1) measures were advised more rapidly, 2) more measures were advised, and maintained applicable for a more extended period, and 3) the level of alertness was significantly higher. Based on these findings, it was concluded that the selected drought indicators support anticipative drought management.