Sean W. Fleming on Where the River Flows

Rivers are essential to civilization and even life itself, yet how many of us truly understand how they work? Why do rivers run where they do? Where do their waters actually come from? How can the same river flood one year and then dry up the next? Where the River Flows by Sean W. Fleming is a majestic journey along the planet’s waterways, providing a scientist’s reflections on the vital interconnections that rivers share with the land, the sky, and us. Fleming recently took the time to answer some questions about his new book.

Your book is unique in that it explores the geophysics of rivers: where their waters come from, why their flows vary from day to day and decade to decade, and how math and physics reveal the hidden dynamics of rivers. Why is this important?

SF: Every aspect of our lives ultimately revolves around fresh water. It’s needed to grow food and brew beer, to build cars and computers, to generate hydroelectric power, to go fishing and canoeing, to maintain the ecological web that sustains the world. Floods are the most expensive type of natural disaster in the U.S., and droughts are the most damaging disasters globally. Yet as the margin between water supply and demand grows narrower, and tens of millions more people congregate in megacities often located on floodplains, we become more vulnerable to the geophysical subtleties of the global water cycle. It’s an important part of life that we need to understand if we’re going to make smart choices going forward.

Your book anthropomorphizes a lot. Is this just a way to make the subjects more accessible, or is there a little more to it?

SF: I ask questions like “how do rivers remember?” and “how do clouds talk to fish?” and “can rivers choose where they flow?” It’s a fun way to broach complicated topics about the geophysics of rivers. But posing questions like that also prepares us to open our minds to new ways of thinking about rivers. For instance, modern information theory allows us to quantitatively describe the coupled atmospheric-hydrologic-ecological system as a communications pathway, in which the weather literally transmits data to fish species using the watershed as a communications channel—modulating water levels almost like Morse code. There may be no intent in that communication, but mathematically, we can treat it the same way.

What are the main threats that rivers face? Are these challenges consistent, or do they vary from river to river?

SF: It does vary, but broadly speaking, watersheds face four main threats: pollution, land use change, climate change, and deliberate human modification. Pollution ranges from industrial effluent to fecal contamination to emerging contaminants like pharmaceuticals. Converting natural areas to urban land uses increases flooding and erosion and reduces habitat quantity and quality. Climate change is modifying the timing, volume, and dynamics of streamflows. And civil works like dams, flood control structures, and of course water withdrawals and consumption, alter river flows and ecosystems more profoundly than perhaps anything else. The common thread behind all these concerns is that human populations and economies—and therefore water needs, and our direct and indirect impacts on rivers—are growing much faster than our development of sustainable technologies.

How will climate change affect river flows?

SF: Global warming is expected to accelerate the water cycle, increasing both flooding and drought. Other impacts are more regional. Some areas will enjoy larger annual flow volumes, whereas others may suffer reduced water supplies. More precipitation will fall as rain instead of snow, and snowpack will melt earlier, changing seasonal flow timing. That may interfere with salmon spawning migration, for example, or render existing water supply infrastructure obsolete. In part due to anthropogenic climate change, mountain glaciers are retreating, effectively shrinking the “water towers” of the Himalayas, Andes, Alps, and Rockies—the headwaters of the great rivers that support much of the global human population, from the Columbia to the Yangtze to the Ganges.

What’s so important about understanding the science of rivers? What does it add to our view of the world?

SF: Just think about floods. Knowing how urbanization or deforestation may affect flooding, or how some kinds of flood control can backfire, or how the flood forecasting behind an evacuation order works, is important for making informed choices. There’s also a philosophical aspect. A dramatic view of a river meandering across a desert landscape of red sand and sagebrush at twilight is made even richer by being able to look deeper and recognize the layers of causality and complexity that contributed to it, from the rise of mountains in the headwaters as a continental plate split apart over millions of years, to the way the river shifts its channel when a thunderstorm descends from the skies to deliver a flash flood.

A consistent theme across the book is the interconnectedness of ideas. Why this emphasis? What’s the significance of those connections?

SF: A fundamental and amazing fact of nature is that not only can so much be so effectively described by math, but the same math describes so many different phenomena. Consider debris flows, a sort of flood-landslide hybrid posing serious dangers from Japan to California to Italy. It turns out we can understand phenomena like debris flows using cellular automata, a peculiar kind of computer simulation originally created to explore artificial life. What’s more, cellular automata also reveal something about the origins of fractal patterns, which occur in everything from tree branches to galaxies to the stock market. Recognizing that ideas from one field can be so powerful in another is important for pushing science forward.

The book seems to present a conflicted view of global water security. It paints an extraordinarily dark picture, but it is also very optimistic. Can you explain?

SF: Grave challenges often drive great achievements. Consider some United Nations numbers. Over a billion people don’t have sufficient water, and deprivation in adequate clean water claims—just through the associated disease—more lives than any war claims through guns. By 2050, global water demand will further increase by a stunning 55%. Little wonder that a former World Bank vice-president predicted the 21st century will see water wars. Yet there’s compelling evidence we can get serious traction on this existential threat. Advances in policy and technology have enabled America to hold its water demand at 1970s levels despite population and economic growth. A focused science investment will allow us to continue that success and replicate it globally.

FlemingSean W. Fleming has two decades of experience in the private, public, and nonprofit sectors in the United States, Canada, England, and Mexico, ranging from oil exploration to operational river forecasting to glacier science. He holds faculty positions in the geophysical sciences at the University of British Columbia and Oregon State University. He is the author of Where the River Flows: Scientific Reflections on Earth’s Waterways.