Forecasting the groundwater levels in the Baltic through standardized index analysis

In regions where groundwater forms the primary source of drinking water, comprehending the prospective availability of subsurface water resources due to climate change is of paramount importance. This study evaluates the impact of climate change on groundwater levels in the Baltic States until the end of this century. It employs link between surface and subsurface standardized indices. For forecast it uses various Representative Concentration Pathways (RCP) alongside different Regional Climate Models (RCM). By linking historical groundwater drought episodes with calculated surface drought indices and accumulation periods observed during defined climate Normals, we project groundwater levels for the short, medium, and long-term future. The study incorporates 13 EURO-CORDEX RCMs under three RCP scenarios. Our analysis reveals that, compared to the recent climate Normals, an overall increase in groundwater levels is expected at most study sites. However, lower groundwater levels are estimated in the near future. The projected impacts show no significant seasonal bias or spatial conformity. Although these findings are specific to the Baltic region, the methodologies described can be readily adapted for global application. • Significant fluctuations in groundwater levels are linked with meteorological conditions from the preceding 7 to 11 months. • A decline in groundwater levels is anticipated in the near future, while an accelerating rise in groundwater levels is expected towards the end of the century. • Temperature is a critical parameter in GWL forecasting. • Extreme conditions may become more frequent during the summer and autumn seasons.