Drought hazard assessment across Sweden's diverse hydro-climatic regimes

Abstract. In recent years severe droughts have significantly impacted the water-dependent sectors including water supply, agriculture, energy, and forestry. This study aims to assess the meteorological, agricultural and hydrological drought risk in Sweden, with a focus on hazard assessment using a set of indicators, including the Standardized Precipitation Index (SPI), Standardized Precipitation and Evapotranspiration Index (SPEI), Standardized Soil Moisture Index (SSMI), and Standardized Streamflow Index (SSI). The indicators were computed at time scales of 1, 3, 6, 12, and 24 months using daily precipitation, evapotranspiration, soil moisture, and streamflow simulations (1975–2021) from the national S-HYPE hydrological model at about 13 km² spatial resolution for almost 40,000 sub-catchments. The drought events were next identified and characterized based on their intensity, duration, and frequency, following this a trend analysis was performed for these indicators and events. Assessing the spatial similarities in soil moisture anomaly led to the categorization of the Swedish river systems into five clusters further improving the understanding of the identified spatial variability of drought indicators and trends. Our findings showed drier conditions and an increasing frequency of droughts in central- and south-eastern Sweden. Significant negative trends in these regions, along with increasingly wet conditions in northern and western Sweden, were observed when analysed using the SPEI, SSMI, and SSI. Based solely on precipitation (SPI), similar significant wetter conditions were observed in northern and western Sweden; however, no significant decreasing precipitation trends were found in parts of central-eastern Sweden and Gotland Island. The findings of this study can improve climate services and early warning systems of droughts, better understanding the link to sectoral impacts and guiding mitigation practices and adaptation policies.