But the regional detail is still important for deciding how, where, and when to respond. Consider the Homestake Reservoir. High in the Rocky Mountains, not far from Vail, CO, it is part of a network of reservoirs and pipelines that feed water to Colorado Springs. In June 2006, the reservoir filled at the unprecedented average rate of nearly two feet per day. Because of higher temperatures earlier in the season, the snowpack was melting more quickly than usual.
The unprecedented may become routine as global warming makes more precipitation fall as rain, while what snow there is melts ever faster. That’s worrisome: a reservoir that fills more quickly than expected can stress a dry levee. And there are other concerns. At what point will earlier snowmelt translate into summer water shortages? Will early spring torrents raise the risk of downstream flooding? Will more-intense spring rainfalls increase sediment, overwhelming filtration systems and washing more pollutants into the water supply? And these climate-related questions arise at a time when rapid population growth is already stressing water resources.
Planners need to understand as precisely as possible the amount, timing, and form–rain or snow–of future precipitation. Only then can they determine when and where to build new water-storage, flood-control, and filtration systems and how to guide future residential or commercial development in watershed areas. So last winter, in a windowless conference room in an industrial area of Colorado Springs, engineers from Colorado Springs Utilities met with David Yates, an NCAR hydrologist, to start revising their water-supply management plans in light of climate-change projections. “Plans are typically made based on historical 20- to 40-year stream-flow averages,” Yates said. “That mode of planning is no longer relevant.”
Concrete local projections are especially important in this region, where politics constrain the way scientific findings can be discussed. Colorado Springs is a politically conservative city and home to a powerful Christian evangelical organization that is skeptical of concerns about global warming. Toward the end of the meeting, the utilities’ manager of water-supply resources, Wayne Vanderschuere, entered the room. He was already thinking about how any new climate-change-related findings might be framed. “All the talk about climate change and CO2–we don’t want to go there. We don’t want to talk about Kyoto, all the posturing,” he said, referring to the Kyoto Protocol, the U.S.-rejected treaty that mandates limits on greenhouse-gas emissions. “We just want the analytic risk to supplying water that this poses.”
Brett Gracely, the utilities’ planning supervisor, said Colorado Springs was at a turning point. “We’re trying to get a handle on what this all means for us,” he said. He–and his city, and the rest of the country–just aren’t sure exactly when and to what extent global trends will influence regional trends and make existing hydrology models obsolete. “If it comes down to literally building a model, how do we do that?” Yates asked during the meeting. “What needs to be done–what resources are needed to do that?” Colorado Springs’ effort to build a model of how climate will affect local hydrology has just begun and could take two years.