Global warming conversations have shifted from whether climate is changing to how we will deal with the inevitable consequences. And the price you pay will depend on where you live and how well you prepare, suggests one of the most detailed studies to date on global warming and its likely effect on human activity. "Like politics, global climate change is local," said Michael J. Scott, a staff scientist at the Department of Energy's Pacific Northwest National Laboratory in Richland, Wash. "Our behavior where we live must change with the climate if we are to meet the challenge Mother Nature may hand us in the next few years." Scott presented findings Sunday from his and colleagues' decade-long case study—on water availability past, present and future in the Yakima River Valley of south-central Washington—at the American Association for the Advancement of Science annual meeting, during a session he organized on adapting to climate change. The Yakima River Valley is a vast fruit basket, with 370,000 irrigated acres of orchards, vineyards and other crops covering 6,150 square miles from the river's headwaters in the Cascade Range east of Seattle to the Yakima's terminus at the Columbia River in Richland. In a typical year, five reservoirs and stream runoff provide agriculture with 2.7 million acre-feet of water. In a typical year at mid-century, that amount will fall an average of 20 to 40 percent. "The expected losses to agriculture alone in the Yakima Valley over the next several decades will be between $92 million at 2 degrees centigrade warming and $163 million a year at 4 degrees"—or up to nearly a quarter of total current crop value, Scott said. Those losses will result from a projected shortage of water for irrigation. That water comes from reservoirs and runoff that are, in turn, tied directly to the amount of snow that accumulates in the Cascades over the winter—the snowpack. Scott, a natural resources economist, and colleagues at PNNL and Washington State University extrapolated the effects of warming to the region by applying data from bad drought seasons going back 80 years to computer projections of diminishing snowpack this century. Models predict up to 70 percent reduction in snowpack for the entire West Coast, including the Cascades. The model they ran assumed no change in precipitation. The key is availability of water when it is needed, not just for agriculture but also for salmon runs and municipal water supplies. The entire system is predicated on water being stored as snow in the mountains becoming available in spring with the thaw. Scott has pinned many of those drought years to El Niño, a disruption of the ocean-atmosphere system in the Tropical Pacific that affects global weather and climate. We have learned from El Niño that small things we can control can help with big things that we cannot, he said. For example, seasonal climate forecasts enable several months' warning that could prevent millions in losses, Scott said. In a typical El Niño year like this one, water managers who monitor reservoir and snowpack levels can assay the likelihood of a coming shortage before January. Unless it snows and rains excessively between now and April (when the official water-availability forecast is made public by the federal Bureau of Reclamation) we can expect water shortages in the Yakima Valley. This information can be put to good use if it comes early enough. If, say, a farmer in an irrigation district that is low in the pecking order—there is a crazy quilt of water districts, and water claims are based on district seniority—knows the spigot will run dry during the coming growing season, he or she can choose to sit out the year. Or that farmer's district can strike a deal with more senior districts to buy their water at a premium and farmers in the senior districts can let low-value crops like alfalfa go fallow, Scott said. El Niño occurs roughly every three to seven years. If there were no El Niño, a severe drought would occur roughly one year in 50. Add El Niño to the mix, and the average frequency for severe drought rises to 1 in 7. The El Niño years themselves average a severe drought year in every three. By conservative estimates, global warming will approximate El Niño severe drought conditions "once every two years," Scott said. With this information, policymakers and farmers can plan ways to adjust practices not just for the next season but for the next several decades. Mitigations can be costly and contentious, such as a proposal to divert water from the Columbia River over the Saddle Mountains into the Yakima Valley (estimated cost: $3.5 billion, but even this is a moving target). More modest and widespread measures could include improved water conservation, water trading and moving up planting and harvesting dates or switching from apples and other water-loving fruits to grapes, which do better than apples on less water. "You're not going to grow apples if you're getting clobbered one season in two," Scott noted. "But you have to plan. It can take years to establish a new crop like grapes." Scott's study has received funding from the National Oceanic and Atmospheric Administration and the Environmental Protection Agency. PNNL (www.pnl.gov) is a DOE Office of Science laboratory that solves complex problems in energy, national security, the environment and life sciences by advancing the understanding of physics, chemistry, biology and computation. PNNL employs 3,900, has a $650 million annual budget, and has been managed by Ohio-based Battelle since the lab's inception in 1965.