Publication Details |
| Category | Text Publication |
| Reference Category | Qualification assignments |
| DOI | 10.25932/publishup-68403 |
Licence  |
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| Title (Primary) | Advancing the spatio-temporal quantification of soil moisture droughts and water deficits in Germany |
| Author | Boeing, F.
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| Year | 2025 |
| Department | CHS |
| Page To | xxv, 158 |
| Language | englisch |
| Topic | T5 Future Landscapes |
| Keywords | climate projections; drought; drought monitor; hydrological simulations; soil moisture; water storage |
| Abstract | Understanding and characterizing droughts and water deficits remains an essential aspect of water resources management. Scientifically, droughts are defined as prolonged periods of below-normal water availability. They occur across various components of the water cycle, such as soil moisture (SM), groundwater, river levels, and lakes. In Germany, the past few years since 2018 have been marked by extreme multi-year droughts, which have raised awareness of the impacts of droughts in Germany - a country that is generally considered to be water-rich. These droughts have negatively affected various sectors such as agriculture, forestry, industry, drinking water supply and tourism, resulting in considerable economic and environmental costs. For effective drought management, it is crucial to address questions regarding the exceptional nature of drought events, the drivers and dynamics of these events, and potential future changes, especially under a changing climate.
The overarching question addressed in this dissertation is how to improve the characterization and understanding of droughts and water deficits in Germany using hydrological simulations. The analyses focus on droughts and water deficits in two important water storages, namely the SM and the terrestrial water storage (TWS), which represents the total water stored on land. Since observations of subsurface water storages such as soil moisture are scarce and the available time series are usually very short, hydrological simulations are employed using models that resolve key hydrological processes. These models enable the generation of long-term, high-resolution datasets necessary for analyzing extreme events like droughts. In this work, the mesoscale hydrological model (mHM) was used to simulate the fluxes and states of the hydrological cycle in Germany. The first part of the research evaluated SM dynamics from mHM simulations, on which the German Drought Monitor (GDM) of the UFZ is based, with a large sample of independent and diverse SM observations. These observations included lysimeters, single profile measurements, spatially distributed observations, and cosmic ray neutron sensing. Good agreement between simulated and observed SM dynamics was found during the vegetation-active period (April to October), while lower agreement was observed in winter due to uncertainties in both simulations and observations. Efforts to improve local relevance by increasing the spatial resolution of the hydrological simulations were motivated by the availability of a new national soil dataset. It was shown that a new version of the GDM with a higher spatial resolution of ≈ 1.2 km moderately improved the agreement of simulations with observations compared to the coarser 4 km version. A resolution of ≈ 1 km is suggested as a suitable compromise for current national simulations of mHM for Germany, considering both the scientific and stakeholder perspective.
In the second part, a long-term perspective on the dynamics of the TWS deficit recovery was provided for the period 1766–2022. Satellite-based TWS estimates, available since 2002, are insufficient for analyzing extremes due to their short time span. Therefore, hydrological simulations were used to extend the analysis. The 2018–2021 TWS deficit was shown to be highly exceptional within the 257-year period, with a recovery time of 31 months (defined as the duration from peak deficit to climatological average) and a mean water deficit of -55.1 mm (-19.7 km³). The analysis revealed that increased evapotranspiration contributed to the prolonged recovery of TWS deficits during this event.
The final part of the dissertation analyzed projections of future SM droughts in Germany using a large ensemble of regional climate-hydrology simulations. The results show that future changes in SM droughts depend on the climate scenario, soil depth, and timing within the vegetative-active period. The most significant increases in SM drought intensity were projected for upper soils during the late growing period July–September under the high-emissions scenario (RCP8.5) in the second half of the 21st century. Uncertainties associated with regional climate models were found to be higher during the early growing period April–June. This dissertation demonstrates how high-resolution and long-term hydrological simulations can improve the characterization and understanding of droughts and water deficits in Germany. Six key pillars for supporting locally-relevant, sector-specific and climate-resilient drought, and water management using hydrological simulations were identified: P1: Evaluation of simulations with independent observations; P2: High-resolution and local relevance; P3: Long-term perspective and variability; P4: System understanding: drivers and patterns; P5: System complexity; P6: Uncertainty and limitations. Scientific evidence and key conclusions for each of these pillars were provided. Hydrological simulations need to be evaluated against independent observations where available. Local relevance with high spatial resolution should be aimed for, although no hydrological model is intended to fully represent reality. A long-term perspective is needed to account for the natural variability of extreme events and to derive robust trends. Understanding of droughts should be improved by analyzing patterns and drivers. The complexity of droughts as well as uncertainty and limitations of hydrological simulations need to be taken into account. The methodological approaches and key pillars outlined in this dissertation are applicable to other types of droughts and water deficits. The approaches can also be applied to other regions, although the applicability depends on local data availability. Finally, large parts of the work contributed to the development of an interactive information system on water resources in Germany (accessible via https://web.app.ufz.de/wis-d/, last access 24 Nov 2024). It is designed to operate at different temporal planning scales using long-term hydrological simulation data covering past reconstructions, present monitoring and future projections. A high degree of regional relevance is achieved through high-resolution hydrological simulations combined with interactive web visualization and analysis tools. |
| Persistent UFZ Identifier | https://www.ufz.de/index.php?en=20939&ufzPublicationIdentifier=31309 |
| Boeing, F. (2025): Advancing the spatio-temporal quantification of soil moisture droughts and water deficits in Germany Dissertation, Universität Potsdam, Mathematisch-Naturwissenschaftliche Fakultät, Institut für Umweltwissenschaften und Geographie xxv, 158 pp. 10.25932/publishup-68403 |
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