Climate model predicts wet winters, dry summers for Northwest US

PNNL scientists tested the new regional climate model on the Northwest – Washington, Oregon, Idaho and western Montana. Assuming carbon dioxide levels will double in the next 80 years as many experts predict, the model shows that in 2080 there will be:

  A 50 percent decrease in snow cover over the entire state of Washington;

  A 50 to 90 percent decrease in snowpack near the existing snow line in Washington state;

  An increase in winter precipitation in the form of rain;

  An average increase of winter temperatures of 1.7 to 2.8 degrees Centigrade;

  An average increase of summer temperatures of 1.1 degrees Centigrade.

The impacts on water resources could be significant, say PNNL project managers. “With less winter snow, we would have less snow melt in the spring,” said Ruby Leung, principal investigator. “We would not have enough stream flow for irrigating crops when we need it most – in June or July.”

“By bringing the issue to a regional level, we help people understand how a global problem could impact them directly,” Leung said. “It’s easier to understand if you know your crops could suffer from lack of irrigation water or your favourite ski resort has to scale back operations.”

The information compiled from this regional climate model is being supplied to the US EPA. The EPA also will use the regional climate change data to estimate how these predicted changes in water resources could affect vegetation.

PNNL’s new regional climate model is a more accurate way of determining global warming’s effects on targeted areas. PNNL scientists begin by using a global climate model to determine the environmental influences in a specific region, such as the Northwest. Influences include surface temperatures, precipitation and snow cover. Then the model merges environmental information such as soil conditions, existing vegetation and surface elevations from subareas within that region to create a more detailed picture of global warming’s impacts. This method is similar to that used in other regional climate models developed in the United States.

However, the PNNL model utilises surface topographic information in the model’s analysis. Therefore, PNNL’s regional climate model can provide climate change data at higher resolutions, which are needed to assess local impacts. The laboratory’s regional climate model incorporates environmental data from areas as small as one square kilometre.