Hydrology Low water, aridity, and drought

Aridity and drought (an exceptionally prolonged and severe period of aridity) are natural phenomena that occur at irregular intervals. In southwestern Germany, for example, this was the case in 1976, 2003, and especially in 2018. Aridity and drought impair the functioning of natural ecosystems and can lead to severe crises in society, with the most frequent impacts occurring in hydrology (low water), agriculture (reduced yields or even crop failures), and public water supply. Climate scenarios suggest that aridity and droughts will occur more frequently in our region in the future.

DRIeR is a research project funded by the State Ministry of Science as part of the Baden-Württemberg Water Network over a five-year funding period (2016–2020). Reflecting the complex nature of aridity, drought, and low water, DRIeR is designed to be interdisciplinary. Scientists from the natural and social sciences departments at the universities of Freiburg, Tübingen, and Heidelberg, as well as numerous other experts, collaborate within DRIeR.

Overall project objectives:

• Interdisciplinary analysis of historical and recent aridity and drought events
• Enhanced collaboration between scientists, decision-makers, and local stakeholders to develop adaptation and mitigation strategies for managing this natural hazard
• Development of a public drought information and collaboration platform
• Improved international visibility of water research in Baden-Württemberg

Our research group in DRIeR focuses on analyzing the impact of aridity on the water balance of the landscape and nutrient fluxes in the soil. To this end, we use intensive monitoring sites to study evaporation, soil water fluxes, and groundwater recharge, as well as nitrate concentrations in seepage water and their dynamics under conditions of aridity. The goal of this research is to gain a deeper understanding of how aridity and drought events alter the water balance and nutrient fluxes in the soil, as well as to incorporate these processes into hydrological models.

To achieve these goals, we conduct field experiments at two agricultural sites in Baden-Württemberg. Groundwater nitrate concentrations are measured at various soil depths and correlated with hydroclimatic variables, physical soil properties, and land cultivation practices. The scope of the study also includes the analysis of long-term water and nitrate fluxes at a forestry observation station in Rhineland-Palatinate.

The results of our field experiments are incorporated into the ongoing development of the TRAIN hydrological model. In addition to the development of a nitrate module and site-specific applications, TRAIN is used for large-scale simulation of water balance components in the states of Baden-Württemberg and Rhineland-Palatinate. The ongoing analyses for the period 1961–2018 focus on the simulated dynamics of water balance components during drought events.