Seasonal Predictability of Hydrometeorological Drought in Sweden

Drought poses a growing risk to society and ecosystems in Sweden, creating major challenges for water supply, agriculture, and emergency response. Although the country has long been regarded as water-rich, recent drought events have exposed significant vulnerabilities and highlighted the need to improve national preparedness. Within this context, the ACT4Drought project, funded by the Swedish Research Council (FORMAS), aims to co-develop an actionable service for drought and water scarcity at sub-seasonal to seasonal (S2S) timescales. We use bias-adjusted seasonal meteorological forecasts from the ECMWF SEAS5 prediction system, which provides ensemble forecasts up to seven months ahead. These forecasts are used to drive the Swedish national hydrological model (S-HYPE) and generate forecasts of soil moisture, discharge and related drought indicators. We evaluate the seasonal predictability of droughts across meteorological, agricultural and hydrological aspects, using the Standardized Precipitation Index (SPI), Standardized Precipitation and Evapotranspiration Index (SPEI), Standardized Soil Moisture Index (SSMI), and Standardized Streamflow Index (SSI) at 1 to 3-month aggregations, and assess their forecast skill across initialization times, lead times and spatial domains. By identifying where and when seasonal forecasts reliably capture drought conditions, this work provides a foundation for more robust operational drought early warnings and advances Sweden’s capacity for drought preparedness.