Validating drought propagation through the entire hydrological cycle simulated with an integrated national-scale hydrological model

Droughts are traditionally associated with warmer, arid climates. However, recent events such as the European droughts of 2018 and 2022, have also highlighted the vulnerability of temperate regions such as Northern Europe. For example, in Denmark the 2018 summer drought led to severe soil water degradation with reported crop failures, surface water degradation, and infrastructural damages due to soil subsidence. Furthermore, climate change studies point towards increasing frequency and intensity of severe droughts.

These events have underscored the importance of understanding how meteorological droughts propagate through the hydrological cycle, transforming into soil moisture and hydrological droughts with distinct response times and magnitudes in different compartments of the hydrological cycle. Due to the close coupling of groundwater to surface waters, and the reliance on groundwater for water supply, drought analysis in Denmark must encompass the entire hydrological cycle in a coupled, integrated manner.

Drought propagation is influenced by numerous factors, including topography, soil types, vegetation, hydrogeology, and human interventions, leading to high spatial variability. While much research has focused on streamflow and soil moisture droughts, the drought propagation across the entire hydrological cycle, where groundwater and its coupling to surface hydrology plays a critical role, remains understudied due to data limitations, particularly at larger scales.

This study leverages the National Hydrological Model of Denmark (DK-model), an integrated, distributed hydrological model, to evaluate drought propagation across all hydrological compartments, from precipitation to soil moisture, streamflow, and shallow and deep groundwater. The DK-model’s nature as an integrated distributed model covering the entirety of Denmark with diverse hydrogeological settings, combined with high observation data availability across the hydrological compartments, provides a unique opportunity to evaluate the model’s ability of reproducing drought events and propagation.

By analyzing model outputs against a large dataset of long-term observations of streamflow, groundwater levels and soil moisture, we comprehensively assess the model’s capability to simulate drought propagation and identify correlations, lag times, and response magnitudes. This work improves understanding of drought dynamics in temperate regions and supports sustainable water resource management in Denmark.