Climate Case Study: California Drought (2)
Climate Case Study: California Drought (2)
In my last blog I explored the current California drought as a climate case study. In my climate case studies I focus on interconnections, for example, how weather and climate influence jobs and behavior. This helps us expose the connections, the management strategies and the policies that are effective or absent. The stresses of climate change will generally amplify the threats due to these events with the expectation, that over the next 3 decades, the climate stresses will increase relative to other stresses. I also made a reaching metaphor to the extinction of large mammals at Agate Fossil Beds National Monument in western Nebraska. The point of the metaphor was to expose the risks of short-term pumping of ground water on longer-term sustainability. In this blog I want to analyze some of the media coverage and a recent paper about the drought.
I would be a deficient blogger if I did not write about the 63 trillion gallons. If you do a search on “63 trillion gallons California,” there will be many hits (LATimes, Mashable). There are pictures of what 63 trillion gallons look like, though not really. This number is drawn from a paper by Adrian Borsa et al. entitled Ongoing drought-induced uplift in the western United States. (Also, though not really!)
This is a nicely written paper, which is, at least currently, not behind a pay wall. The paper examines several hundred ground-based Geographical Positioning Systems (GPS) sensors. These sensors have been placed in the ground over the past couple of decades, primarily to help measure how the surface of the Earth is moving. Back when I was at NASA in the late 1990s, these were being placed in the ground of Southern California. It was part of an investigation to inform, ultimately, earthquake prediction. Now there is a network of more than 800 sensors in the western part of the U.S., west of a line running, north-south, from western New Mexico and Colorado, central Wyoming and east-central Montana (longitude 109W). This line is west of the Continental Divide, in Colorado and New Mexico, which is relevant because it captures most of the Colorado River Basin, an important part of the California’s water picture.
The first point of the paper is, in my opinion, that this data system is of sufficient precision and adequate coverage that the rise and fall of the Earth’s crust due to the changing surface and ground water can be measured. The second point is that they can distinguish between wet and dry years, and in 2014, a time of exceptional drought, the crust of the Earth has risen in some places up to 15 millimeters, which is a little more than a half an inch. That’s a pretty cool measurement. The cause of this rise is loss of water, and of course, a loss of the water’s mass, which effectively changes the local gravity field.
The authors talk about the rise of the land being equivalent, at its maximum, to a decrease of about 50 cm of water. 50 cm is about 20 inches. When they calculate this water loss, they state it is consistent with changes in stream flow and precipitation. By consistent, they mean that they calculate the budget of water mass and, within their levels of uncertainty, the numbers match. The authors state that the total mass loss is equivalent to 10 cm of water (about 4 inches), spread over the entirety of the study area. To my knowledge the number of gallons of water were not mentioned in the paper, but I did not check the online supplemental information. It’s an easy enough calculation.
This relation between the measurement of rise and fall of the Earth’s surface and precipitation, evaporation and stream flow is what leads the authors of the paper to conclude, “Our analysis shows that the existing network of continuous GPS stations in the western USA measures vertical crustal motion at sufficient precision and sampling density to allow the estimation of interannual changes in water loads, providing a new view of the ongoing drought in much of the WUSA (Western United States of America).” The authors do not pose this measurement, their number, as a measure of exceptionalism or extremes. (There is another interesting number in the paper. The authors calculate that the change in stress along the San Andreas fault is equal to about a week’s worth of the normal strain due to the motion along the fault.)
One of the problems I have with the press coverage is that this 63 trillion gallons and the change in the Earth’s crust is out of context of any other numbers. It is the first time the measurement has been made, not the first time there has been the change in the water sufficient enough to change the Earth’s elevation. There are also many pictures showing depleted reservoirs, again out of context. If one were so inclined, then one could find many inconsistencies and allusions, which would be open, potentially, to criticism of exaggeration. All of this is generated by the reportage on the paper on points that, to the best of my reading, were not made in the paper. Looking around with my favorite search engines, I can find a number of stories and pictures that, often with the best of intentions, are adding more extreme, more emotional adjectives to describe the drought. (Oh, Rood, are you going down the alarmist path? Ye, of the Beardogs?)
In my wandering around on the California drought, I came across the prolific writing and videos of Jay Famiglietti. Jay and I have mingled in the same worlds for much of our careers and were co-authors on a National Strategy for Advancing Climate Modeling. In Op-Ed’s, blogs and his scientific writings, Famiglietti is laying out the essential need for California, and by extension for the U.S., to develop rational, sustainable water policy. Looking at supply and demand, if the current drought continues as current conditions suggest, California will soon be down to a water supply of months. Even if there is an exceptional period of rain that ends this particular drought, the stresses of residential demand, agricultural demand and climate change will soon, again, converge to crises that erode community, productivity and economy.
Jay Famiglietti: How Much Water Does California Have Left? An nice piece on how water management and keeping the population centers hydrated place the problem out of sight out of mind.
Jay Famiglietti: Can We End the Global Water Crisis?
Castle et al.: Groundwater depletion during drought threatens future water security of the Colorado River Basin (open access, a more important paper about California water than the paper discussed in this blog)
Figure 1: Figure from Randall Munroe of xkcd.com. This graph shows a time series from 2000 to 2014 of the extent of the graph. Details are provided at this link on explainxkcd.com. (Yes, I would be science happier if "ludicrous" was not used, but it is a good graph, and it has the dates. Many of the images appear in other graphs but with no dates.)
Here is a nice Infographic from the LA Times: 191 drought maps, with dates.
Note: The changes in the land associated with removal and addition of water have many of the same causes and effects as the effects of sea level rise on land. There have been large amounts of sinking in parts of California’s Central Valley due to pumping of ground water. Some of the basic concepts are in my blog Sea-level Variability: A Primer.
Understanding California’s Groundwater / Water in the West
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