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Managing dams for a changing climate

Issue 2 and Volume 114.

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Civil engineers at the University of Washington and the U.S. Army Corps of Engineers’ Seattle office have taken a first look at how dams in the Columbia River basin, the nation’s largest hydropower system, could be managed for a different climate.

They developed a new technique to determine when to empty reservoirs in the winter for flood control and when to refill them in the spring to provide storage for the coming year.

Computer simulations showed that switching to the new management system would lessen summer losses in hydropower due to climate change by about one quarter. It would also bolster flows for fish by filling reservoirs more reliably. At the same time the approach reduced the risk of flooding.

Predicted hydrologic changes for the Pacific Northwest and other mountain regions include less springtime snowpack, earlier snow melt, earlier peaks in river flow and lower summer flows. Water managers currently use a system based on historical stream-flow records to gauge when to open and close the floodgates.

The researchers created a computer program that uses long-term forecasts rather than historical records to recalculate when to begin filling and emptying the major storage reservoirs. They compared historical conditions with a scenario where temperatures are 2 degrees Celsius higher on average than today, a change expected in the Pacific Northwest by the second half of this century.

The simulations suggested water managers could successfully deal with warmer conditions by refilling the system’s reservoirs as much as one month earlier in the spring.

The project aims to help regional water managers develop methods to deal with changes in the hydrological cycle.

 

Asian ozone affects North America

 

Springtime ozone levels above western North America are rising primarily due to air flowing eastward from the Pacific Ocean, a trend that is largest when the air originates in Asia.

Such increases in ozone could make it more difficult for the United States to meet Clean Air Act standards for ozone pollution at ground level, according to a new international study. Published online in the journal Nature, the study analyzed large sets of ozone data gathered since 1984.

“In springtime, pollution from across the hemisphere, not nearby sources, contributes to the ozone increases above western North America,” said lead author Owen R. Cooper, of the NOAA-funded Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder. “When air is transported from a broad region of south and east Asia, the trend is largest.”

The study focused on springtime ozone in a slice of the atmosphere from two to five miles above the surface of western North America. That slice is below the protective ozone layer but above ozone-related, ground-level smog that is harmful to human health and crops. Ozone in this middle region constitutes the northern hemisphere’s baseline level of ozone in the lower atmosphere. The study was the first to analyze nearly 100,000 ozone observations.

Fossil fuel combustion releases pollutants like nitrogen oxides and volatile organic compounds, or VOCs, which react in the presence of sunlight to form ozone. North American emissions contribute to global ozone levels, but the researchers did not find any evidence that these local emissions are driving the increasing trend in ozone above western North America.

The study used springtime ozone measurements because previous studies have shown that air transport from Asia to North America is strongest in spring. That makes it easier to discern possible effects of distant pollution on the North American ozone trends.

The analysis shows an overall increase in springtime ozone of 14 percent from 1995 to 2008. When the scientists included data from 1984, the year with the lowest average ozone level, they saw a similar rate of increase from that time through 2008 and an overall increase in springtime ozone of 29 percent.

 

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