Here is a new one from Jay Famiglietti & friends. I love the play on words in the title; I would call it a double entendre without the risqué interpretation. Why not quantify something with grace? Better than with mercilessness or ineptitude!
'Quantifying Renewable Groundwater Stress with GRACE', by Alexandra S. Richey, Brian F. Thomas, Min-Hui Lo, John T. Reager, James S. Famiglietti, Katalyn Voss, Sean Swenson, and Matthew Rodell, Water Resources Research, DOI: 10.1002/2015WR017349
This article is not copyright protected; if you click here you can access the online version where you can use the hot links in the article. Or you can download the PDF below.
Renewable groundwater stress is quantified in the world’s largest aquifers
Characteristic stress regimes are defined to determine the severity of stress
Overstressed aquifers are mainly in rangeland biomes with some croplands
Abstract. 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 avail- ability 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 nega- tive) 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.
[Click on the graphic to enlarge it.]
I have not gone through this paper in great detail but wanted to post it because it's important. Richey et al. develop some simple stress indicators [See my post on Lenny Konikow's depletion intensity.] for large aquifer systems.
The first paragraph of the conclusions are disappointing:
It is important to understand where existing socio-economic tensions may collide with water stress to produce stress-driven conflicts [ICA, 2012; U.S. Department of State, 2013]. However, the definitions of water stress by both the U.S. Department of State and the United States Agency for International Development (USAID) depend on either the Falkenmark Indicator or a high ratio of withdrawal statis- tics to availability [ICA, 2012; U.S. Department of State, 2013]. The Falkenmark Indicator does not account for groundwater as a water supply source or water use that is not driven by population density, such as irrigated agriculture. We have shown that simply quantifying water use based on withdrawal statistics cannot fully capture the range of impacts that groundwater use has on groundwater systems.
Not good. Our government can do better. I trust they will read this work.
Richey et al. have done a very good job. In fact, Jay Famiglietti and his colleagues have done a remarkable job in putting Earth's groundwater resources front and center. For that they deserve our kudos. But it's important to remember:
1) GRACE data have poor spatial resolution - on the order of 150,000 square kilometers (58,000 square miles) or worse. That's an area about the size of Illinois or Georgia. So GRACE will provide useful information for large aquifer systems.
2) GRACE data say nothing about groundwater stocks - the volume of groundwater in storage.
3) Ground truthing is important when dealing with remotely-sensed data. Boots on the ground and all that.
5) Avoid irrational exuberance.
Time to go.
“Everybody gets so much information all day long that they lose their common sense.” - Gertrude Stein