Many of Earth’s Groundwater Basins Run Deficits

Climate and human consumption are parching Earth’s groundwater basins at an alarming rate, a new study finds

Of Earth’s 37 biggest groundwater basins, 21 now lose more water annually than they take in, researchers report in a paper to be published in  Water Resources Research .

That’s troubling, says study coauthor Sasha Richey, a hydrologist at Washington State University in Pullman. Groundwater quenches the thirst of about 2 billion people, provides irrigation for crops and helps keep wetlands wet.

Groundwater is an increasingly important water supply source globally. Understanding the amount of groundwater used versus the volume available is crucial to evaluate future water availability. We present a groundwater stress assessment to quantify the relationship between groundwater use and availability in the world's 37 largest aquifer systems. We quantify stress according to a ratio of groundwater use to availability, which we call the Renewable Groundwater Stress ratio.

The impact of quantifying groundwater use based on nationally reported groundwater withdrawal statistics is compared to a novel approach to quantify use based on remote sensing observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. Four characteristic stress regimes are defined: Overstressed, Variable Stress, Human-dominated Stress, and Unstressed.

The regimes are a function of the sign of use (positive or negative) and the sign of groundwater availability, defined as mean annual recharge. The ability to mitigate and adapt to stressed conditions, where use exceeds sustainable water availability, is a function of economic capacity and land use patterns.

Therefore, we qualitatively explore the relationship between stress and anthropogenic biomes. We find that estimates of groundwater stress based on withdrawal statistics are unable to capture the range of characteristic stress regimes, especially in regions dominated by sparsely populated biome types with limited cropland. GRACE-based estimates of use and stress can holistically quantify the impact of groundwater use on stress, resulting in both greater magnitudes of stress and more variability of stress between regions.

Source: Science News

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• Research
• Groundwater
• Hydrology