From the weather forecast to the push notification: Switzerland's new drought warning system

Droughts in Switzerland have become more frequent and severe in recent years, and this trend is expected to continue. At the same time, increasing water demand and competition between different actors are putting more pressure on existing water resources, leading to drought being rated within the top 10 costliest potential hazards for Switzerland. A comprehensive national monitoring and forecasting system, to be launched in 2025, is being established through the joint efforts of three different government agencies.

We will present the Swiss national drought monitoring system with a particular focus on the web platform and the operational warning system, both of which were developed in close collaboration with local decision-makers and end-users. The information system is a public web platform synthesizing various data streams (i.e. precipitation, streamflow and groundwater, space-based monitoring of vegetation health and land surface temperature) and provides homogeneous forecasts of drought quantities with a horizon of four weeks. Historical observations and sub-seasonal forecasts are merged to provide seamless information on drought that can be easily and interactively compared to action-relevant thresholds as well as historical events. The main drought variables are also summarized into a combined drought index which is used to provide an overall evaluation of the situation and forms the basis for drought warnings. Starting from 2025, drought warnings will be released by national agencies through official channels in the same way as they already are for other natural hazards like floods or heatwaves, over national web platforms and push notifications on the MeteoSwiss mobile App (2.5 million visits per day). The two-tiered warning strategy was designed in collaboration with end-users and authorities to take into account some of the particularly challenging aspects of drought compared to other natural hazards. These include, among other things, the need for sector-specific and impact-oriented information, and the difficulty for a national system to accurately reflect the highly heterogeneous and localized mitigation measures that are of most interest to the end-users during an extreme event.

Analysis of the historical 2018 drought shows that the forecasting system would have correctly triggered a response at the level of regional authorities 1.5 months ahead of the event peak. A higher-level and more broadly visible warning would have been released again a month later, about two weeks ahead of the event peak. We will conclude with an overview of future plans and of the event-based feedback mechanisms through which end-users and regional authorities will contribute to improving the warning system and our ability to track drought impacts at the local scale.