Where global warming meets the faucet
Boulder, CO - No matter where you live, climate change is going to affect your water supply. In some places it could mean tearing out a lawn. In others it might mean channeling torrential rain away from your house and local infrastructures. Projecting what exactly will happen to municipal water supplies – city by city – and how to plan for it is what keeps researchers like at Richard Palmer of the University of Washington busy.
Palmer and his colleagues specialize in taking the broad strokes of global climate models and refining and customizing them to foresee what climate change is likely to do in particular specific water-supply basins. The closer look is just what local and state governments and water planners need to make sure taps don't go dry.
Palmer is scheduled to present his methods and what they reveal on Tuesday, 19 September, at the Geological Society of America conference on Managing Drought and Water Scarcity in Vulnerable Environments: Creating a Roadmap for Change in the United States. The meeting takes place 18-20 September at the Radisson Hotel and Conference Center in Longmont, Colorado.
Seattle and Portland have already been studied in this way, and even cities in wetter climes like Atlanta may benefit from the same treatment soon, as water supplies get tighter.
"In the Pacific Northwest most of the cities are served by water supplies which are transient," said Palmer. "They rely specifically on spring run-off." That run-off is from mountain snow packs that are changing as climate warms.
"You can see decrease in snow pack over the past 50 years already," said Palmer. "So what this is saying is that the natural (snow pack) reservoir is getting smaller and smaller. In the winter of 2005 we had the smallest snow pack on record. That's a real wake up call for us that something is changing."
To determine more precisely how the changes in the snow pack are likely to change the water supplies of Seattle and Portland, Palmer and his team first gathered up climate data forecasting the years 2020, 2040, and 2060 from the latest, most advanced global climate models – those which are already being used to create the 2007 climate report by the Intergovernmental Panel on Climate Change (IPCC). Then, because the IPCC models are very geographically coarse, with even states like Washington, for instance, covered by only four to eight boxes in a global grid, Palmer and his colleagues downscale the models so they make sense on a local level.
Downscaling, in this case, means adding in local digital elevation map data to account for the local topography, the distributions of vegetation types, soil types, as well as adding all sorts of local hydrological data. When they are done, the local water basin models "see" the regions as arrays of boxes, each box about the size of a football field. That sort of resolution provides a far more realistic view of what global changes will do locally.
Next, they calibrate the model by applying it to the past. When the new model can reproduce what has happened in the past, it's a fairly safe bet the local models will produce reasonable predictions of what will happen in the future, given various scenarios.
Finally, Palmer's team adds in the actual water supply operations, which is where the rubber meets the road. "At the end of this they are trying to replicate how people operate water supply systems," he said.
Under the IPCC's "Business As Usual" scenario, in which greenhouse gases continue to increase, Palmers group found that both Portland and Seattle will see higher peak stream flows in the winter and lower summer flows. That's basically because global warming will continue to move the snowline higher and more water will fall as rain.
"The quantity of water for June through September decreases by six percent per decade, therefore 24 percent by 2040," Palmer reports. The good news is that part of that water is lost into the ground, so it can be recovered via wells. But it still effects what's called a "safe yield" of water. "How much water can you supply at a reliable level will change three to four percent per decade," said Palmer. "That's the bad news."
Fortunately, people and city governments are ahead of the game. They have already taken action and changed their water consumption.
"Even though the population has grown, in Seattle area the water demand is the same as in the late 1970s," said Palmer. "The average per capita water consumption has decreased significantly."
The Seattle and Portland studies could be replicated in places like Atlanta, Washington D.C., or Boston, where droughts and water crises have lead to worries in recent decades.
"Atlanta wants more water from the Chattahoochee River," said Palmer. But that water is shared with many users, including hydropower plants and all the way down in the Florida Panhandle for oyster farming.
"Climate change is heightening the sensitivity of these issues," Palmer said. "On the Potomac River they are seeing the same thing we are seeing in Seattle. Water is being used much more wisely."
In other places, like New England, climate change may bring more water, which could be just as much trouble to plan for as less water, says Palmer. "The impact on some of these places will be storm flow, which will still require multibillion dollar projects."
WHEN & WHERE
The Impacts of Climate Change on U.S. Water Supply
Tuesday, September 19, 8:45 a.m. MT, North & South Summit
Radisson Hotel & Conference Center
1900 Ken Pratt Boulevard, Longmont, CO 80501
Richard N. Palmer
Department of Civil and Environmental Engineering
University of Washington, Seattle, WA
E-Mail: [email protected]
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