Groundwater is the earth’s most important freshwater resource that supplies water to billions of people and plays a central role in irrigated agriculture and influences health of many ecosystems. Currently, groundwater is abstracted at rates that exceed recharge from groundwater and rivers and groundwater is depleted. An indicator of groundwater stress is the groundwater footprint (GF). The GF, defined as the area required to sustain groundwater use and groundwater-dependent ecosystems, is a previously published as a suitable tool for consistently evaluating the use, renewal, and ecosystem requirements of groundwater at an aquifer scale (Gleeson et al 2012). However, Gleeson et al. used a hydrological model, representing the groundwater as a linear reservoir, therewith probably overestimating groundwater contribution to streamflow resulting in overestimated GFs (Alley et al 2017). A more accurate assessment of GFs of aquifer systems worldwide can be expected if a gradient groundwater flow model would be used.

- Use different methods to quantify groundwater’s contribution to environmental flows using simulated outputs of groundwater recharge, groundwater discharge, and streamflow from the global groundwater model PCR-GLOBWB-MF (developed in our group). (examples are Gleeson and Richter 2017, Pastor et al 2014)

- Use the different quantified groundwater contributions to estimate GFs following Gleeson et al (2011). This will give us an uncertainty of the estimated GFs worldwide.

- We will evaluate the new estimated GFs against the old GFs, and experiment with different scales to present GFs at (while a spatial scale smaller than the aquifer is probably more relevant for water managers).

- Preferable, results will also be evaluated against more specific regional scale estimates.

You should have an interest in large-scale hydrological and groundwater modelling and you should want to learn how to work with a complex large-scale model. This involves working on a supercomputer, scripting in python and R. You should have taken the modelling courses of the MSc program. The language of the thesis will be in English.

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

tba

Gleeson et al 2012: Water balance of global aquifers revealed by groundwater footprint, nature.

Alley et al 2017: Groundwater Development Stress: Global-Scale Indices Compared to Regional Modeling, Groundwater.

Gleeson and Richter 2017: How much groundwater can we pump and protect environmental flows through time? Presumptive standards for conjunctive management of aquifer and rivers, River res. Applic.

Pastor et al 2014: Accounting for environmental flow requirements in global water assessments, HESS.