Quantifying groundwater resources from satellites

Groundwater is one of the most important freshwater resources for ecosystems and human societies. It has a fundamental role in the Earth’s water and energy cycles. However, it is the most difficult water compartment to quantify in a direct way.

The Global Climate Observing System (GCOS) recently decided to declare groundwater as an Essential Climate Variable (ECV), promoting projects aiming at the quantification of its past, present and future variations. Funded by the EU Horizons 2020 program, the G3P project aims at developing a global product of groundwater storage variations from satellite gravimetry. The World Glacier Monitoring Service (WGMS) – hosted at GIUZ – will contribute with the development of a observational global glacier change product.

G3P – The Global Gravity-based Groundwater Product

The G3P strategy is simple: Gravity Recovery and Climate Experiment GRACE (2002-2017) and its follow up GRACE-FO (since 2018) are satellite missions aiming at measuring the Earth’s gravity field and its variation in space and time. They are able to observe spatial and temporal variations of total water storage (TWS) on all continental areas of the Earth.

Rapid retreat of Jorge Montt glacier (Patagonia, Chile) observed from space. Animation by Etienne Berthier from ASTER images.

If we quantify independently the water storage variations of glaciers, snow, soil moisture and surface water bodies from other Earth observation satellites or models, we can calculate the variations in groundwater storage by the following subtraction process:

Being part of the G3P consortium, the WGMS working group at University of Zurich will contribute with the development of a purely observational global glacier variation product readily extractable from the GRACE signal. During the project period from 2020 – 2023, we will combine the glacier outlines and glacier volume and mass change series – provided by the Copernicus Climate Change glacier services – into a global assessment of glacier mass changes at an improved spatial and temporal resolution, with yearly updates.

This allows us to monitor each individual glacier and its annual and seasonal variations. The resulting worldwide glacier product will be directly subtracted from the GRACE total water storage signal to calculate the variations in groundwater storage for the G3P project. Results will also be available for further academic research involving recent local, regional and global glacier changes.

G3P – The Global Gravity-based Groundwater Product
World Glacier Monitoring Service (WGMS)

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