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People need to be in the equation too, says Circle of Blue report Brett Walton.

Photo © J. Carl Ganter / Circle of Blue

Homes and farms cover Kern County, in California’s Central Valley. In addition to rain and snow, drought assessments need to account for the influence of human demands. Click image to enlarge.

For a society in thrall with performance reviews, business analytics, and the Fitbit, it is an appealing calculation: how much rain will end the California drought?

Like asking how many calories to cut to lose five pounds, the question reflects an American sense of goal setting and stocktaking. Where are we now? Where do we need to be? How do we get there? It is a query in the style of Peter Drucker, father of management theory: we can manage what we can measure.

This question of California’s rain deficit was put to a pair of urban designers last week by a participant in an online Q & A hosted by the technology blog Gizmodo . Hadley and Peter Arnold are the executive directors of the Arid Lands Institute, an urban design institute in Burbank, California, that focuses on adapting the American West to water scarcity.

In response to the question, the Arnolds noted that there is no single way to answer. But they duly attempted a back-of-the-envelope calculation based on a statewide groundwater deficit of 63 trillion gallons that NASA’s GRACE satellites measured between January 2013 and August 2014. California, they reckoned, would need at least eight, maybe nine more storms comparable to the 10-day gusher that soaked the state last December .

Though appealing — the Gizmodo story had been liked 263 times on Facebook at the time of this article publishing — this line of inquiry is incomplete. It minimizes the concept of drought to one variable: supply. Even more, it reduces supply to a single subset: rainfall. As more and more researchers are beginning to realize, understanding drought requires a broader frame. Humans need to be a part of it.

Defining Drought

The Arnolds’ response at least took the answer in the proper direction. Instead of rainfall, they considered the groundwater deficit – how much more water must be added to return the system to the pre-drought balance. By doing so, they introduced a human component (groundwater withdrawals) to the natural component (water that filters into the aquifers via snowmelt and rainfall).

A human component. This, perhaps surprisingly, is a relatively new way of analyzing drought. Researchers for the longest time looked to the sky and to rivers to study drought.

“Drought used to have basically two definitions: precipitation and streamflow,” Michael Dettinger, a U.S. Geological Survey hydrologist, told me last December at the American Geophysical Union conference in San Francisco, where drought was a trendy topic .

That limited view went out the window a few decades ago, but it still

clings in some sectors, and, apparently, with the public.

One of the most encompassing definitions of drought that I’ve has come from Kelly Redmond, a climatologist at the Western Regional Climate Center. In a commentary published in 2002 in the Bulletin of the American Meteorological Society, Redmond argued for a broad definition, a definition that transcends drought’s meteorological origins. His pithy assessment: insufficient water to meet needs. Explaining, Redmond wrote:

“Most concepts of drought involve a water balance. This implies that both supply and demand must be considered, as well as the question of whether there is ‘enough’ (and, enough for what?). Thus, through time I have come to favor a simple definition; that is, insufficient water to meet needs. This covers a broad range of situations, from an asteroid to a Pacific Ocean beach, if need be. By intention, it highlights the importance of both the supply and the demand sides of the issue. From this standpoint, a system is ‘in drought’ when supply does not meet demand. Such could occur from diminished supply with relatively constant demand, or from relatively constant supply and increased demand.”

–Kelly Redmond, climatologist at Western Regional Climate Center

Constant supply with increased demand — in other words, a manmade drought. In this scenario, rainfall is not the problem; it is the crowding at the trough. One look at the great river deltas and lakes that have dried up around the world is enough to confirm the problem.

Other scientists have made similar points.

Mark Svoboda, a climatologist at the National Drought Mitigation Center in Lincoln, Nebraska, told me three years ago for a story about the U.S. Drought Monitor. a now-common national drought ranking, that more demand for water increases the severity of dry conditions and heightens the vulnerability of dry regions.

Some of the most interesting current drought research takes this tack.

Anne Van Loon is a hydrologist and lecturer at the University of Birmingham, in England. She is also the chair of a research project called “Drought in the Anthropocene ,” which will examine how society influences drought and vice versa — through intensive groundwater use, for instance, or by the spread of urban pavement, which can alter river flows and cut aquifer recharge by putting an asphalt lid on the spongy ground.

“We should take steps to include the human aspects of drought,” Van Loon told me in December. “We can have a drought in a relatively wet situation.”

So rain is one drought variable, but it is not the whole equation. Maybe the new question should be: how much water will we use before we trigger a drought of our own making?

How do you think about drought? Do you see responses that take the human element into consideration? Add your thoughts in the comments below, send me an email at, or ping me on Twitter at @waltonwater.

–Brett Walton, reporter

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