Groundwater Storage Anomalies

As the largest store of accessible freshwater on Earth, groundwater is under increasing pressure as a resource, currently underpinning a large proportion of irrigated agriculture worldwide and being the source of drinking water for around 2 billion people.

The large storage capacity of aquifer systems offers exceptional drought resilience and enhances water security, but aquifer overexploitation can hinder this capacity as well as harm groundwater-dependent ecosystems, cause aquifer salinisation and land subsidence, among other issues. Thus, continuous monitoring of groundwater resources is crucial; however, in-situ measurements are rarely available due to the high cost of drilling and maintaining wells, the decentralised or non-digitalised nature of data collection, and, in some cases, political restrictions that prevent public access to data. EO technology made an important breakthrough with the Gravity Recovery and Climate Experiment (GRACE) and its Follow-On (GRACE-FO), which provide information on water content in the different layers of the soil based on changes in the Earth’s gravity field.

This EO capability will help decision makers detect areas with significant ongoing groundwater depletion where the resilience of groundwater resources, and the dependent socioeconomic activities, are at stake. In this way, environmentally sustainable storage limits and extraction rates can be estimated for areas where aquifers present consistently low groundwater storage levels and/or are currently being overexploited. These areas can then be considered for the potential application of managed aquifer recharge practices. Large-scale assessments of groundwater recharge and storage variations can be derived from the combination of EO data and data assimilation systems such as GLDAS Land Surface Models (Noah, CLSM, and VIC), which provide information on snow water equivalent, surface water, canopy water, and soil moisture data.

The estimation of groundwater storage anomalies constitutes the building block for groundwater resources assessment based on EO, serving as the baseline from which other EO capabilities are derived, such as groundwater quantification and abstraction, groundwater drought assessment, and climate to groundwater correlations.