Understanding the global freshwater system by combining geodetic and remote sensing information with modelling using a calibration/data assimilation approach (GlobalCDA)

Project summary
Contemporary global hydrological (or land surface) models provide conflicting estimates of e.g., mean annual evapotranspiration or low, mean, and high flows in river basins, resulting in strongly differing estimates of current water availability or of climate change impacts on freshwater resources. Therefore, the central objective of the GlobalCDA project is to improve our understanding of global freshwater resources and to obtain better estimates of continental water fluxes and storages through combining state-of-the-art hydrological modelling and multiple new and optimally processed geodetic and remote sensing data in an ensemble-based calibration and data assimilation (C/DA) approach that allows a flexible parameter (calibration) and state (data assimilation) adjustment tailored to the modelling purpose. Such an approach, which would additionally take into account uncertainty due to model structure, has not been implemented yet.

Therefore, two primary goals have been defined for the project: (1) develop a multi-observation ensemble-based C/DA methodology to combine observational data of model output variables with hydrological models in an optimal manner, and (2) exploit this methodology with the global hydrological model WaterGAP to provide an improved quantitative assessment of freshwater fluxes and storages including their uncertainties in response to climate and anthropogenic forcing. The eleven principal investigators and two Mercator fellows in nine individual projects contribute in this project leading in hydrological model development, remote sensing, and in the emerging field of hydrogeodesy. More information can be found on the project webpage.

Our contribution
Within GlobalCDA, the goal of project P2 is to contribute to the development of a flexible calibration and data assimilation (C/DA) approach for the state-of-the-art global hydrological model WaterGAP that will enable WaterGAP to better simulate water flows and storages by making best use of multiple observational data for model output variables. P2 will contribute to design and evaluation of the C/DA approach, provide model variants, validate C/DA results and assess model output uncertainty. In addition, P2 aims at advancing hydrological process simulation by new WaterGAP model components, with a focus on development and integration of a global gradient-based groundwater model that improves the simulation of groundwater-surface water interaction and allows quantification of capillary rise. Besides, a floodplain inundation component and glacier water balances are to be integrated. Regarding assessment of water flows and storages in large critical regions, P2 will lead the study on the Tigris-Euphrates-Western Iran region.

Prof. Dr. Petra Döll (principal investigator)
Dr. Seyed-Mohammad Hosseini-Moghari
Sebastian Ackermann

June 2018 – Jun 2024

German Research Foundation (DFG)

See project webpage