High-Resolution Climate Models Reveal Increasing Meteorological Drought Intensity in Fenno-Scandinavia

Climate projections indicate that Fenno-Scandinavia will experience increased precipitation in the future. However, the region might paradoxically face both intensified floods and more severe seasonal droughts. Little research has explored this apparent contradiction and its implications for drought frequency. Most of the current drought projections are based on global climate models with very low resolution. In this study, we use convection-permitting regional climate models (CPRCMs) based on HARMONIE-Climate at a resolution of about 3 km to investigate meteorological drought projections in Fenno-Scandinavia. For the first time this model was run for 20-year time slices (1986-2005, 2041-2060 and 2081-2100), allowing for climate analysis with explicitly resolving convection rather than relying on parameterisation, giving overall more accurate precipitation output.

Using the Standardized Precipitation Index (SPI), we found an increase in the frequency of the most extreme and unprecedented meteorological droughts. Southern Scandinavia experiences a significant increase in the most extreme droughts, especially during the growing season. To identify these increases in drought extremes, we developed a new drought threshold method using the fact that the index is standardised to compare future drought frequency to historical data. This method does not use a single drought definition, but rather compares the drought frequency for multiple intensities. Importantly, our results show significant increase in droughts projected using the 3 km convection resolving models compared to the 12 km models with convection parameterisation. This indicates that current regional climate models possibly underestimate drought risk. The projections indicate larger crop yield reduction due to short but severe dry spells during the growing season and potential impacts on natural ecosystems. The combination of overall wetter conditions with more intense seasonal droughts presents new challenges for water resource management. We recommend the usage of the drought threshold method to analyse drought projections in order to also take the intensity of the drought into account. Future work will apply the new drought threshold method to regional climate model ensemble data for greater robustness.