University of Calgary

Water in the works

UToday HomeDecember 3, 2012

Patrick Wu, left, and Holger Steffen co-authored a paper showing the recovery of groundwater after a long drought in the prairies.Patrick Wu, left, and Holger Steffen co-authored a paper showing the recovery of groundwater after a long drought in the prairies.Many Canadians, especially in Saskatchewan and Alberta, may still remember the extreme Canadian prairies drought between 1999 and 2005. A significant low in precipitation produced the worst drought for at least the past 100 years.

A team of researchers from the Chinese Academy of Sciences in Wuhan, China, and the University of Calgary, has published a paper ’Increased water storage in North America and Scandinavia from GRACE gravity data’ this week in Nature Geoscience showing that the amount of water stored in the prairies is recovering significantly since 2003.

“This is the first study that clearly shows large-scale hydrological changes over the huge area of central North America,” say co-authors of the paper Patrick Wu, professor, and Holger Steffen, postdoctoral fellow in the geoscience department.

Together with their Chinese colleagues, they developed a new method to separate the hydrological signal from observations of the GRACE (Gravity Recovery and Climate Experiment) satellite mission.

“The difficulty so far was that GRACE observations consist of many overlapping signals. In North America, the signal of glacial isostatic adjustment – that is the ongoing rebound of the earth due to melting of the ice sheets from the last Ice Age – is enormous and completely overshadows the hydrology signal. It was common practice to use models of insufficient accuracy for enhancing this signal, which led to inadequate interpretations,” explain the researchers. ”Using GPS measurements and our special mathematical method, the water changes are now clearly identified, and we don’t have to rely on the models anymore.”

The mass change in central North America, including the Great Lakes, is about 43 gigatons per year.

“This is about three quarters of all water falling down Niagara Falls every year,” Steffen says. “And the number also has implications on global sea-level and climate change studies, as this value would be equivalent to 0.13 mm per year of sea-level fall.”

The researchers also identified a mass increase in northern Europe, but at a much slower rate.

“Our result will greatly improve existing hydrology models for both areas as we can finally provide exact predictions of long-term terrestrial water changes, which are needed as input for these models.” adds Wu. ”Besides monitoring floods and droughts, as well as water level in large lakes, the separated GRACE data can be used to understand solid earth processes, too.”