Marc Bierkens maps the world’s freshwater to spotlight global supply and demand

The Dutch hydrologist’s innovative water map urges viewers to mind the world’s growing ‘water gap’

Photograph courtesy Marc Bierkens

It didn’t take long for National Geographic Explorer Marc Bierkens to catch what he calls “the research virus,” at his first hydrology internship. A graduate student at Wageningen University in his native Netherlands, he spent a year abroad at the University of California, Davis’ Department of Land, Air, and Water Resources to supplement his studies in hydrology and water management. His time there, and at a subsequent research internship studying groundwater, elbows deep in data, were early inflection points that led him to pursue his Ph.D. at Utrecht University, and a career in water research. 

“It was a lot of very technical, methodological work, coming up with smart statistical methods to analyze data and so on,” Bierkens reflects on those first years of research, “but I wanted to do something that speaks more to the imagination of the general public.”

Now, Bierkens is a professor of hydrology at Utrecht, where he has been able to realize his grander ambitions of high-impact research for the past two decades. His current efforts are focused on leading the recently launched World Water Map. Developed with hydrology researcher Niko Wanders, with support from the National Geographic Society and in cooperation with Utrecht University and Esri, the new Map forms a central piece of the Society’s five-year World Freshwater Initiative to better understand global water shortages and inspire sustainable solutions.

The Map is a unique geovisualization of global freshwater availability and agricultural, industrial, and domestic water usage over time, using data to tell the story of how humans have used water from as far back as the 1980s through present day. Most importantly, it identifies 22 water hotspots–regions around the world where water demand outstrips the amount made available from renewing resources each year—a worrisome water gap. Just like money drawn out of an emptying savings account, Bierkens says, “This is water that is taken out of storage; this is groundwater depletion.”

The World Water Map has its roots in groundwater depletion research Bierkens and his team at Utrecht have been investigating since 2009, with the building of their own global hydrological model. By comparing how much water was available from the hydrological system to how much was being used by humans based on socioeconomic data, the team created one of the earliest maps of global groundwater depletion hotspots, which identified regions in India and California. 

Remarkably, their model’s information was corroborated by similar findings from NASA’s GRACE satellite mission, which identified many of the same hotspots by tracking the movement of water from its gravitational pull. Comparatively, “We found [these hotspots] indirectly, just by doing the bookkeeping!” Bierkens marvels.

The hydrological models that power this newly launched World Water Map, which plots hotspots all over the world, are the product of countless data sets collected by several organizations and universities. The intricate parameters and sheer volume of information functioning behind the scenes to ensure accuracy are astonishing. “It's not easy to estimate how much rain falls on earth and how much runs into the oceans every year,” Bierkens admits.

To account for the natural hydrological system—what is essentially the water cycle through Earth’s land, oceans, and atmosphere—data is amassed from years of National Weather Service forecasts, satellite images produced by NASA and the European Space Agency, global climate models by The Intergovernmental Panel on Climate Change, digitized soil and geological maps, and more. 

“This is stuff that’s on the shelf, being renewed every few years, that we can use,” Bierkens says. “Without them, we could not do what we do.” Together, this data informs the research team’s hydrological models of many variables: global soil types and their water holding capacities, the dimensions of surface water like rivers and oceans, precipitation and evapotranspiration, and surface vegetation.

“And then you have to go do the human system,” Bierkens continues. “This means dams and reservoirs.” Scientists have been mapping reservoirs themselves by looking at aerial photographs and employing remote sensing. According to Bierkens, tools and innovations like Google Earth and artificial intelligence have made reservoir mapping even easier over time. “We currently have about 7,000 of the largest reservoirs accounted for, but there are new data sets that show close to 20,000 or 30,000 reservoirs. So our model is improving every day.”

The final piece to account for is human water use, which Bierkens calls “a statistical exercise.” Population density maps for each country and satellite imagery of the Earth’s electric lights at night show where human concentrations lie, and thus, where industrial water usage follows. In addition, a country’s GDP per capita represents how wealthy the population is, an important predictor of both domestic and industrial water usage.

The largest proportion of human water usage lies in the agricultural sector, mainly irrigation, which consumes about 70% of global freshwater sequestered in surface and groundwater systems. Armed with data on crop types, weather, and plant water uptake and transpiration, Bierkens’ hydrological model can calculate the water necessary for irrigation in any given 10-square-kilometer area. 

It’s a mind-boggling amount of synthesis—in a world where data is so ubiquitous, Bierkens recognizes the complex process of assembling this Map. “Now, when I reiterate what is needed to make a model run like that,” he laughs, “I’m also actually surprised at the amount of work that’s gone into it.”

But to Bierkens, the work is justified. He hopes the Map will have far-reaching impacts, prompting national and global policymakers to explore the evolution of water availability and encouraging action where water gaps are in dire need of attention. 

His biggest wish, however, is for the Map to touch the general public; it has been purposefully fashioned with interactive layers and accessible language, in line with Bierkens’ vision of introducing the concept of water literacy to interested civilians at any level. “I quite like the term ‘water literacy,’” he smiles. “What's the water gap? How does it build up, and how will it develop in the future? What does water balance look like?” 

With this tool, Bierkens hopes viewers begin to probe these critical questions regarding water availability and scarcity: “It’s important that people become aware of what water issues exist globally and how much these will affect their lives.”

Over the next five years, the World Fresh Water Initiative will fund National Geographic Explorers working in freshwater science, conservation, education, and storytelling.

This Explorer's work is funded by the National Geographic Society
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For the National Geographic Society: Melissa Zhu is a content strategy coordinator at the Society.

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