Should we include lateral groundwater flows in global-scale hydrological models?

Groundwater is the world’s largest accessible source of freshwater and plays a vital role in satisfying basic need of human society. During dry periods, groundwater storage provides a natural buffer against water shortage, preserves evaporation in areas with shallow water tables, and sustains baseflows to rives and wetlands. Also, groundwater often flows across catchment boundaries at considerable rates, supporting water budgets of receiving catchments. Despite the importance of groundwater, most global-scale hydrological models do not include a groundwater flow component. The main reason of this missing component is the lack of consisting data. However, when current global-scale models move to finer resolutions, lateral groundwater flows across cells will get more important.

In this study we want to explore and quantify the effect of including lateral groundwater flows in a global global-hydrological model at different spatial scales, on different processes.

The following main research questions can be formulated:

1. How large is the groundwater contribution on water budgets of catchments or aquifers? How does this change with human water uses or changes in climate? (MSc project 1).

2. How are e.g. river drainage or energy fluxes influenced by lateral groundwater flows? How does this change with human water uses or changes in climate? (MSc project 2).

Both research topic will start with data analysis on previous model runs, with and without a groundwater flow component (the model that will be used is PCR-GLOBWB-MODFLOW). The data analysis includes model validation against available global-scale datasets or other model outcomes (e.g. discharge data, baseflow index maps). Potentially, new model runs will be done, e.g. for smaller parts of the world at higher resolutions.

These projects require to apply and further develop skills and data processing and analysis (e.g. in R). General knowledge about modelling obtained during the MSc courses is needed. Programming skills and experience with Linux is not required. However, willingness to learn is a must. Also, an interest in global-hydrology is required.

English

First: Dr. Inge de Graaf (inge.de.graaf@hydro.uni-freiburg.de)

Second: tba

Global hydrological model: e.g. Van Beek et al. (2011), Global monthly water stress: 1. Water balance and water availability, WRR.; De Graaf et al. (2017), A global-scale two-layer global groundwater model, ADWR.

Shaller and Fan (2008), River basins as groundwater exporters and importers: Implications for water cycle and climate modelling, J. of Geoph. Res.; Kollet and Maxwell (2008), Capturing the influence of groundwater dynamics on land surface processes using an integrated, distributed watershed model, WRR.