Relationships between low-flow-indices and groundwater levels in Lower Saxony, Germany

In recent years, Europe has experienced severe droughts (2018-2020) due to reduced summer precipitation and high temperatures, leading to reduced runoff and groundwater levels. According to climate change projections, these conditions will become more frequent. These droughts have significant impacts on ecosystems, drinking water supplies and navigation, for example.

During such dry periods, rivers are mainly fed by groundwater. The aim of this study is to statistically analyse the interaction between surface water discharge, especially during dry periods, and groundwater levels. For 128 catchments in Lower Saxony, Germany, correlations between selected low flow characterising indices and groundwater level indices are calculated. Therefore, groundwater levels from spatial interpolation of shallow, unconfined aquifers were aggregated at the catchment level. The study focuses on mean and minimum groundwater levels over different monthly time periods as well as the standardised groundwater level index (SGI) to reveal possible patterns and relationships with low flow indices. We expect to find non-linear correlations particularly between the SGI and specific low flow indicators such as lowest 7-day average flow (NM7Q), deficit volume and low flow duration. A further aim is to investigate whether these relationships can be used to improve statistical models, such as multiple linear regression, to provide a predictive framework for low flow conditions based on groundwater levels. Such relationships and correlations may improve our understanding of how groundwater levels can act as an additional predictor of low flow conditions.