REWET - PREdicting, origin, and validating of non-rainfall Water in agricultural EcosysTems using energy balance model, water stable isotopes, and lysimeter data

• Applicant: Dr. Jannis Groh
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 460817082

Dew, hoar frost, fog, and water vapour adsorption in soils are the least studied and characterized components and processes of the terrestrial water cycle. Within the REWET project, these components and processes are quantified for different agro-ecosystems in humid areas and important contributions to the understanding of the processes are developed. The components have not been considered in most studies dealing with the simulation of ecosystem processes, as their measurement is costly and methods for prediction are only of limited applicability. In REWET, the frequency and duration of these components and their quantities will be determined exemplarily for eight different agroecosystems. The quantification will be based on data from high-precision weighable lysimeters as well as leaf wetness and meteorological measurements. In the first step of the project, the driving abiotic and biotic factors that control the formation of dew, hoar frost, fog, and water vapour adsorption in soils of the respective agro-ecosystem will be identified. It is expected that, in addition to atmospheric conditions, surface temperature and the structure of the canpoy play a decisive role in the formation of these components. The identified key factors and measurements will then be used to predict and validate the formation mechanisms using the Two-Source Energy Balance Model TSEB. The implementation of the surface temperature and calibration of land surface parameters (e.g. aerodynamic resistance) will help to capture the formation processes in the model. The TSEB model use standard meteorological parameters and should enable a better estimation of these components at the landscape level in the future. The dew and fog water will be sampled for more than one year to identify the sources of the dew and fog fractions. The isotope composition of the water and its position in relation to the local meteoric water line varies according to the origin and formation mechanism of the component (e.g. ocean, evaporation). Knowledge of the source of origin can help to estimate possible effects of climate change on the formation of dew and fog. To determine the significance of dew, fog or water vapour adsorption in soils as additional components of the water balance for plant growth, the stable isotopes in plant water and their water potentials are measured daily during a dry period. Due to different fractionation processes, the water in the plant can be assigned to dew, fog or soil water based on the slope δ17O-δ18O. This can clarify whether the plants can take up this intercepted water directly through the leaf and thus reduce water stress in plants during dry periods.

• DFG Programme: Research Grants
• International Connection: France, USA
• Cooperation Partners: Dr. Daniel Beysens; Dr. Paul D. Colaizzi; Dr. Steve Evett