Weeks before rising floodwaters devastated Calgary and other municipalities along the Bow River, a hint of the impending disaster was apparent in data from a pair of NASA satellites.
Observations by the the Gravity Recovery and Climate Experiment show groundwater in the region has been at progressively higher levels than average – leaving the land with little extra capacity to take up additional water coming in from rainfall and melting snow. The find underscores a crucial relationship between changing groundwater levels and flood potential, and suggests groundwater monitoring needs to be at a higher priority so that officials can include it in their planning.
"The role of groundwater is often overlooked, in particular when it comes to flooding and drought," said Jay Famiglietti, a hydrologist at the University of California, Irvine, and a member of the GRACE science team.
Earlier this month, Dr. Famiglietti published data that shows groundwater levels dropping across much of the southwestern United States, where drought and extensive use of aquifers for irrigation have collectively taken a toll on the amount of water below the surface. In contrast, groundwater in the northern U.S., particularly around the upper Missouri River basin, has shown a marked increase because of more rainfall, a predicted byproduct of climate change.
GRACE consists of two satellites in a low orbit about 220 kilometres apart from each other. As they skim over the planet, scientists monitor how their separation is affected by slight differences in Earth's gravitational field. The method is sensitive enough to weigh the volume of water stored underground in different parts of the world by measuring its gravitational pull on the passing spacecraft.
Although the published map does not include Canada, Dr. Famiglietti says the upward trend continues north and west into Alberta. The gravity data show that groundwater can play a significant role in increasing the flood hazard there and, if the trend continues, severe flooding like that seen over the past several days will be a recurring threat.
"If you pay attention to this type of this data … you can see that the flooding is inevitable," he added. "It is like a bucket filling up with water. It can only hold so much."
Dr. Famiglietti is one of several experts converging this week to discuss groundwater issues at the University of Toronto's Munk School of Global Affairs. The meeting also coincides with the release of a report Tuesday from the Munk school that finds Canada critically deficient in the mapping and monitoring of groundwater across the country.
The report lists GRACE as a potential source of data that water managers should be incorporating into models that project what will happen to groundwater in the future. It notes that the U.S. is well ahead of Canada in mapping out its is principal aquifers, and warns that Canada's relative lack of information about its own water resources could put it at a disadvantage in future disputes over waters that span the border between the two countries.
"We know far more about underground oil and gas …than we do about our underground water," said James Bruce, another presenter at the conference and the chair of an expert panel on groundwater management convened in 2009 by the Council of Canadian Academies.
About one-third of Canadians depend on groundwater for household use. Increasing pressures on the resource in many parts of the country include the intensification of agriculture and the growth of hydraulic fracking for natural gas extraction. It is expected that in many drought-prone regions, climate change will add a further burden. This makes a more detailed assessment of groundwater all the more important for decision makers on both sides of the border, the Munk school report argues.
Dr. Famiglietti agrees. "I don't believe that we have the political and legal infrastructure in place to deal with the water issues of the future," he said.