Future changes in frequency and intensity of meteorological and hydrological droughts in Denmark

Drought frequency is projected to increase in mainland Europe while decreasing in Scandinavia under climate change, placing Denmark in a hydro-climatic transition zone with an uncertain future. This makes Denmark a relevant case for analysing future changes in the meteorological forcing and hydrological response, that can ultimately lead to substantial implications for agriculture and water resource management.

We investigate future changes in drought frequency and intensity in Denmark up to 2100, combining regional climate model simulations (Euro-CORDEX), which were adjusted using observational data to produce Klimaatlas Denmark, and hydrological model outputs from the National Hydrological Model of Denmark. Drought conditions are analysed using standardised indices representing different components of the hydrological cycle, including precipitation (SPI), precipitation-evapotranspiration balance (SPEI), soil moisture (ESSMI), streamflow (SDI) as well as shallow and deep groundwater (SGDI). We compared these indices using a drought multi-threshold method for a consistent comparison across variables.

Results show a clear seasonal signal in meteorological drought, with decreasing frequency in winter and increasing frequency in summer. Accounting for evapotranspiration further amplifies projected summer drought conditions. In contrast, streamflow and groundwater droughts are projected to decrease in frequency towards the end of the century across most of Denmark. However, extreme droughts may still lead to risks of groundwater depletion, due to increased demands for irrigation water abstraction during dry summers.

These findings demonstrate that changes in meteorological drought do not directly translate to streamflow and groundwater drought responses in Northern Europe. Further, they highlight the importance of accounting for drought propagation through multiple compartments of the natural system and the overlying signal of water provisioning when assessing future drought risks.