BMBF: Drought early warning systems for carbonate aquifers (GRaCCe)

Quantification of resilience of water resources in carbonate aquifers to drought conditions

Carbonate aquifers are widespread worldwide and contain important water resources. Because of their high hydraulic conductivity, low storage coefficient, and associated low storage capacity, they are sensitive to hydrologic events.

The water volume stored in the water-unsaturated zone can be considerable, especially when thick vadose zones are present. As water scarcity becomes more common due to climate change, understanding and predicting infiltration dynamics is highly relevant.

In addition, intelligent management of water stored in the vadose zone can reduce the impact of dry periods on water resources and thus reduce the intensity of droughts.


The GRaCCE research project focuses on quantifying and predicting short- and long-term droughts under Mediterranean climates. The project combines:

  • hydrogeophysical measurements at a field site in Rüdersdorf (Brandenburg) to identify optimal monitoring techniques for quantifying water fluxes in the unsaturated zone of karst aquifers,
  • adaptation of transfer functions to calculate groundwater recharge in the double continuum of karst aquifers,
  • application of the transfer functions to data from the Western Mountain Aquifer in Israel and the Palestinian Territories for rapid prediction of future groundwater recharge events and droughts,
  • incorporation of the transfer function into the drought early warning system and support from groundwater management.

Flow paths in the vadose zone

Figure 1: Infiltration behavior of water along preferred flow paths in the vadose zone.

Transfer Function

Figure 2: Illustration of the relevant components of the vadose zone which the transfer function determines (left) and of the transfer function and the various distribution functions in the frequency domain (right).

The transfer function describes the vadose zone as a "black box". The transfer function consists of information about the input (precipitation) and output (groundwater recharge), from whose Power Spectral Density (PSD) the transfer function is determined in the frequency domain. With the transfer function, precipitation signals can be converted into groundwater recharge. The mean flow velocities as well as the stored water volume can also be determined.

Since the transfer functions in the GRaCCE project are applied in carbonate aquifers, the different seepage velocities along the fractures and interaction with the matrix have to be considered. This is done by a tripartition of the frequency ranges with different distribution functions. The normal distribution, the "white noise signal", represents the fast groundwater recharge along fractures, whereas the gamma distribution represents the interaction of the fractures with the matrix and the exponential distribution represents the slow flow component in the matrix.

Development of an early warning system for droughts

Figure 3: Work packages from all project partners to develop a drought early warning system and apply it to a climate projection to 2070.

Project details

Project coordination

University of Göttingen
TU Berlin

Lead: Prof. Dr. Irina Engelhardt

Other national partners

Helmholtz Centre for Environmental Research - UFZ
VisDat geodatentechnologie GmbH

International partners

Ben-Gurion University of the Negev, IL
Hydrological Service Israel, IL
Hydro-Engineering Consultancy, PS
Palestinian Water Authority, PS
Palestinian Hydrology Group for Water and Environmental Resources Development, PS
Al al-Bayt Universität, JO


The project is sponsored by the German Federal Ministry of Education and Research (BMBF) as part of the Middle East Regional Water Technology Cooperation Program (MOST).

Funding code:

Project duration: 2021-2024