My Ten Cents - Paper: 'Human Domination of the Global Water Cycle Absent from Depictions and Perceptions'

The Paper
I have been meaning to post this paper for over a month. I saw Jay Zarnetske mention this work during a talk on another topic. Here it is: Human Domination of the Global Water Cycle Absent from Depictions and Perceptions, Nature Geoscience, volume12, pages 533–540 (2019).

The author list is reminiscent of those particle physics papers: Benjamin W. Abbott, Kevin Bishop, Jay P. Zarnetske, Camille Minaudo, F. S. Chapin III, Stefan Krause, David M. Hannah, Lafe Conner, David Ellison, Sarah E. Godsey, Stephen Plont, Jean Marçais, Tamara Kolbe, Amanda Huebner, Rebecca J. Frei, Tyler Hampton, Sen Gu, Madeline Buhman, Sayedeh Sara Sayedi, Ovidiu Ursache, Melissa Chapin, Kathryn D. Henderson & Gilles Pinay 

Download Human_Domination_Absent_Global_Water_Cycle

Here is a very good online copy of the article: click here.

Abstract
Human water use, climate change and land conversion have created a water crisis for billions of individuals and many ecosystems worldwide. Global water stocks and fluxes are estimated empirically and with computer models, but this information is conveyed to policymakers and researchers through water cycle diagrams. Here we compiled a synthesis of the global water cycle, which we compared with 464 water cycle diagrams from around the world. Although human freshwater appropriation now equals half of global river discharge, only 15% of the water cycle diagrams depicted human interaction with water. Only 2% of the diagrams showed climate change or water pollution—two of the central causes of the global water crisis—which effectively conveys a false sense of water security. A single catchment was depicted in 95% of the diagrams, which precludes the representation of teleconnections such as ocean–land interactions and continental moisture recycling. These inaccuracies correspond with specific dimensions of water mismanagement, which suggest that flaws in water diagrams reflect and reinforce the misunderstanding of global hydrology by policymakers, researchers and the public. Correct depictions of the water cycle will not solve the global water crisis, but reconceiving this symbol is an important step towards equitable water governance, sustainable development and planetary thinking in the Anthropocene.

Below are some figures of what the authors would (presumably) love to see. Click on them to enlarge them or view them online. Note that pools (stocks) of water as well as fluxes are shown with uncertainties.

This figure shows some of the effects of human interference with the water cycle.

Here is another such diagram.

You get the picture.

My Approach
The authors make some excellent points. One thing that I dislike about many hydrologic cycle (I don't often say 'water cycle') is that they give little consideration to groundwater. Maybe they show an arrow buried somewhere. This negligence is understandable; most diagrams focus on flows, not stocks (or pools), and so surface and atmospheric waters dominate. My cryologist/glaciologist friends could also make the same case about glaciers and icecaps.

Here are two global hydrological cycle diagrams from my favorite physical hydrology textbook, Elements of Physical Hydrology, 2/e by G. Hornberger et al.

Pretty simple, right? No houses, factories or shopping centers, though.

Here's the companion figure, showing annual volumetric fluxes in relative units (100 units = 119,000 cubic kilometers per year). 

Groundwater is pretty visible even though its flux is pretty small. These two figures are accompanied by a table with stocks and residence times. It's best to use this table in conjunction with these diagrams.

Here is a 'local' hydrologic cycle I use, created by a friend - the 'Post-Modern Hydrologic Cycle'. It shows that water flows to money - so you know humans are involved. I always explain this when I use it... Students seem to enjoy it. 

The USGS has a bunch of diagrams - click here.

MyTen Cents
Do I think my approach is wrong? You'd think that after 47 years of teaching this stuff I'd get it right!

The authors have done us a great service by pointing out the problems with most depictions of the hydrologic cycle. Sure, humans and their activities (climate change and others) are affecting the cycle at all spatiotemporal scales and will continue to do so. But the cycle has been around for billions of years and will be around long after we leave. I like to point that out. Must be the geologist inside me.

I will likely continue to use the versions I have been using. They are simple to explain and very helpful in elucidating the basic hydrologic processes. I can describe the difficulty in estimating stocks, flows and residence times. I can show how climate change will likely alter things. I can ask the students about the diagrams' shortcomings and what the cycle might look like at a regional or local level. And what about water quality? Where is that? Is it important? How could we insert water quality into the picture?

One thing I've started  doing on exams (take-home as well as in-class): asking students to draw and label their own hydrologic cycles. Sometimes I ask them to do a region-specific one. Maybe where they grew up. Or maybe I'll ask them what's wrong with the ones I use.

One thing I will continue to do (with some exceptions): keep the ocean in the picture of most cycle diagrams I use. I thought about this when an audience member in New Mexico asked me sarcastically, "Why do you have an ocean in your diagram? We're hundreds of miles from the nearest shore!". My reply silenced him: "Where do you think your precipitation originates?" No matter where you are on Earth the oceans matter. 

But this paper made me think and examine my own shortcomings. So you should all read it. Teachable moment for sure!

Enjoy!

"Inside every silver lining there's a dark cloud." - George Carlin (as Al Sleet, the Hippy Dippy Weatherman, 1960s)

Comments

[Richard Cathcart]

thanks for posting "human domination of global water cycle..." NATURE paper! You might wish to look at new interpretations of the "rock cycle" done. Some indicator papers are posted, and freely downloadable, at ResearchGate.com
sincerely,
Richard

[Mehdi Mirzaee]

Hi Michael

Thanks. That was awesome.
Decision makers almost has a good sensation of money (do they?? Really???) And I think that we have to change our water cycle to such that.
Best