Groundwater

	It is estimated that groundwater accounts for about 30% of the world’s total freshwater resources, and it is by far the largest available reservoir of liquid freshwater. Groundwater counts in average for one third of the freshwater consumed by humans, but at some parts of the world, this percentage can reach up to 100%. Climate change affects groundwater recharge rates through changes in precipitation and evapotranspiration. However, attributing observed groundwater change to climate change is difficult because of the influence of land-use change and groundwater abstraction. The extent to which groundwater recharge and storage has already been affected by climate change is widely unknown. Climate change can also affect groundwater through saltwater intrusion in coastal aquifers as sea level rises.
	Domain:	Terrestrial
	Subdomain:	Hydrology
	Scientific Area:	Hydrosphere
	ECV Steward:	Claudia Ruz Vargas, Andreas Güntner
	Products:	Groundwater Storage Change, Groundwater Level

Groundwater level

Figure: Groundwater level time series of well 32_16, Sweden from 01/01/1976 until 23/01/2019, extracted from the Global Groundwater Monitoring Network (GGMN).

ECV Products and Requirements

ECV Product / Definition / Units

Groundwater Storage Change / The volumetric loss or gain of groundwater between two times period / km³ y^-1 (or mm y^-1)

Groundwater Level / The level (depth or elevation) of the water table, the upper surface of the saturated portion of the soil or bedrock / m

Products			Groundwater Storage Change		Groundwater Level
	(*)	Unit	Values	Unit	Values
Horizontal Resolution	G	km	≤ 100	number of wells per 100 km²	-
	B				-
	T		200-300		1
Vertical Resolution	G		-		-
	B		-		-
	T		-		-
Temporal Resolution	G	month	0.5	month	0.5
	B		1		1
	T		3		3
Timeliness	G	month	<1	y	2-3 (days)
	B		1		0.5
	T		12		1
Required Measurement Uncertainty (2-sigma)	G	mm y-1	1	mm	1
	B
	T		10		30
Stability	G	mm y-1	1		1
	B
	T		10		10

These products and requirements reflect the 2022 GCOS Implementation Plan (GCOS-244) and the 2022 GCOS ECVs Requirements (GCOS-245).

(*) Goal (G): an ideal requirement above which further improvements are not necessary. Breakthrough (B): an intermediate level between threshold and goal which, if achieved, would result in a significant improvement for the targeted application. The breakthrough value may also indicate the level at which specified uses within climate monitoring become possible. It may be appropriate to have different breakthrough values for different uses. Threshold (T): the minimum requirement to be met to ensure that data are useful.

Data Sources

This list provides sources for openly accessible data sets with worldwide coverage for which metadata is available. It is curated by the respective GCOS ECV Steward(s). The list does not claim to be complete. Anyone with a suitable dataset who wishes it to be added to this list should contact the GCOS Secretariat.

Global Gravity-based Groundwater Product (G3P)

https://doi.org/10.5880/G3P.2023.001

http://gravis.gfz-potsdam.de/gws

Global Groundwater Monitoring Network (GGMN) by the International Groundwater Resources Assessment Center (IGRAC)