Keynote lectures

Invited speakers and topics:

Marc Bierkens

Marc Bierkens

Professor of Hydrology at Utrecht University, Chair of Earth Surface Hydrology Group, Department of Physical Geography, Senior Scientist at Deltares, Unit Soil and Groundwater systems

Utrecht, Netherlands

Global groundwater modelling and the limits of groundwater use

Population growth, economic development, and dietary changes have drastically increased the demand for food and water. The resulting expansion of irrigated agriculture into semi-arid areas with limited precipitation and surface water has greatly increased the reliability of irrigated crops on groundwater withdrawal. Also, the increasing number of people living in mega-cities without access to clean surface water or piped drinking water has dramatically increased urban groundwater use. The result of these trends has been the steady increase of the use of non-renewable groundwater resources and associated high rates of aquifer depletion around the globe. To analyse the effects of human water use on the terrestrial water cycle and in particular groundwater resources, global hydrological models have become an important tool. In this talk I will start with an overview of the global hydrological modelling efforts to date that have been used to estimate global groundwater depletion and provide examples of estimated depletion rates. I will also introduce estimates from a newly developed global groundwater model. I will argue that global groundwater models are required to move the field of global groundwater sustainability from depletion rates to limits of groundwater use in terms of attainable volumes and expected time horizons. I will provide preliminary results on exploring three types of limits: physical limits (how much groundwater is physically extractable in terms of quantity and quality), environmental limits (how much can be extracted before environmental flow requirements are compromised) and economic limits (what is the groundwater depth at which extraction costs become too high for the given economic use of groundwater).

Jens Birkholzer

Jens Birkholzer

Senior Scientist, Director for the Energy Geosciences Division, Lawrence Berkeley National Laboratory

Berkeley, California, USA

Geologic Carbon Sequestration at Scale: A Review of Basin-Scale Pressure Impacts, Induced Seismicity Concerns, and Pressure Management Opportunities

After decades of research on carbon capture and sequestration (CCS), the world needs to finally move from pilot tests and demonstration experiments to industrial-scale implementation. CCS at scale will involve unprecedented fluid injection volumes that can result in large-scale pressure increases in the subsurface and may cause unwanted geomechanical effects, such as generating seismic events per reactivation of critically stressed faults. Understanding and predicting induced seismicity potential is critical in CCS projects for two reasons: (1) to avoid the potential for damaging earthquakes at the ground surface, and (2) to ensure that caprock integrity is not jeopardized by permeability increases of slipping faults. Also, in a future world with CCS being a fully deployed technology, sedimentary basins with interconnected reservoirs might host multiple storage sites between which pressure interference can be expected. Thus, large-scale pressure buildup can be a limiting factor for CO2 sequestration capacity, because of induced seismicity concerns or because the possibility of distant pressure-related impacts of individual projects needs to be considered. It has been pointed out that the subsurface storage capacity for CO2 may be increased via extraction of the native brines, a pressure management approach that of course comes with additional cost for the handling, treatment or disposal of the extracted brine and thus needs to be carefully optimized. This presentation will illustrate the basin-scale pressure impacts based on regional modeling studies of future CCS scenarios, will discuss the potential for generating earthquakes from CCS at scale using the practice of waste water injection in Oklahoma and surrounding States in the U.S. as an analog, will present a controlled-injection fault slip experiment to advance the science of fault reactivation and related permeability change, and will finally evaluate brine extraction as a mitigation measure currently tested in a field experiment located in the southern United States.

Rolf Reichle

Rolf Reichle

Research Physical Scientist, NASA Goddard Space Flight Center

Greenbelt, Maryland, USA

Remote sensing and assimilation of soil moisture and terrestrial water storage at the global scale

Recent satellite missions have revolutionized land surface hydrology at the global scale. Observations from the Gravity Recovery and Climate Experiment (GRACE) mission provide monthly global estimates of the vertically integrated terrestrial water storage with about 300–400-km horizontal resolution. The Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions observe L-band (1.4 GHz) microwave brightness temperatures, which are sensitive to near-surface soil moisture, with a revisit time of 1–3 days at ~40-km spatial resolution. Through the assimilation of these remote sensing observations into a land surface model, value-added estimates of global land surface hydrology conditions can be obtained with complete spatial and temporal coverage. One example is the SMAP Level-4 Soil Moisture data product, which provides global, 3-hourly, 9-km resolution estimates of surface and root-zone soil moisture and associated land surface variables.
This presentation discusses recent results obtained from the assimilation of GRACE, SMOS, and SMAP observations. As expected, GRACE data assimilation mostly improves estimates of shallow groundwater, whereas SMOS and SMAP data assimilation mainly improves estimates of surface soil moisture, particularly in otherwise data-sparse regions. Better and more consistent soil moisture and groundwater estimates can be achieved when multiple observation types are assimilated.  Nevertheless, open questions remain about the synergy of GRACE, SMOS, and SMAP observations and land surface models. An example in northwestern India illustrates that long-term trends in GRACE observations result in erroneous trends in evapotranspiration estimates if irrigation is not considered in the land surface model, thereby emphasizing the importance of representing anthropogenic processes in land surface modeling and data assimilation systems.