New Map Offers Better Look at World’s Water-Logged Regions

Until recently, when ecologists wanted to study aquatic ecosystems at a large spatial scale, they had to rely on maps that weren’t exactly fine-tuned. In fact, these satellite-generated maps were assembled from plot points of 25 square kilometers.

New Global Inundation Map. Courtesy: Etienne Fluet-Choinard
New Global Inundation Map. Courtesy: Etienne Fluet-Chouinard

To get a sense of that scale, says Etienne Fluet-Chouinard, such a map would combine all of the Yahara Lakes into a single visual data point, or pixel. Sure, the result would reflect that there’s a lot of water here in Madison, but such a broad brush stroke lumps several different ecosystems and land types into a single blue dot. Fluet-Chouinard is a second year PhD student in Pete McIntyre’s group here at the Center for Limnology,
Etienne Fluet-Choinard
Etienne Fluet-Chouinard

To address this problem and get a more detailed look at water on the earth’s surface, Fluet-Chouinard, and a team of other researchers paired the usual satellite imagery with more detailed topographic maps. Thanks to gravity (and the fact that water flows down hill) the researchers were then able to accurately predict where water would be and create a new map at a much higher spatial resolution. Their result was published in the journal, Remote Sensing of Environment on the first of this month.
“We went from 25 by 25 kilometer pixels, to a 500 square meter pixel size, so a 50 time decrease in size,” Fluet-Chouinard says. “That gives you more resolution, and also allows you to distinguish between distinct water bodies and features – which for ecologists is important.”
For example, he says, if a scientist is going to study something like fish biodiversity in relation to floodplains or look for broad-scale changes like the loss of wetlands over an area, then the old maps would leave valuable data out of the mix. The new map catalogs everything from lakes, rivers and wetlands to things like rice paddies and seasonally water-logged  croplands.
“This is crucial first step to classifying freshwater ecosystem types at the global scale,” Fluet-Chouinard says. “We have good maps of where rivers and lakes should be, but seasonal wetlands, like the Amazon floodplain, are really hard to pick up, and you can’t do it with just satellites.”
The new map represents a great asset for scientists to better understand large inundation patterns and wetland ecosystems, he says.
Citation: Fluet-Chouinard, E., Lehner, B., Rebelo, L.M., Papa, F., Hamilton, S.K., Development of a global inundation map at high spatial resolution from topographic downscaling of coarse-scale remote sensing data, Remote Sensing of Environment (in press),