Rogue Basin Climate Trends and Projections

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Rogue Basin Climate Trends and Projections

By Alan Journet Ph.D. Co-facilitator, SOCAN

As we lead up to Earth Day on April 22nd, Insight to Ashland and Southern Oregon Climate Action Now offers a four-part series on the environment. The series will include Rogue Basin Climate Trends and Projections, Keystone XL Pipeline concerns, What We Can Do, and a Q&A with SOCAN.

When Mt. Ashland Resort managers commented upon the late opening of the ski season, they expressed surprise that snows were coming later than ‘normal’. Apparently, like many of us, they are not paying attention to climate trends. Regrettably, historic averages no longer instruct us about the future. A more accurate picture can be gained only by
examining historic trends.

Local climate history and trends are available from NOAA which provides Medford data comparing mid-century (1930-1980) to late-century (1981-2010) averages. Additionally, data from the USFS in Corvallis, used in a report authored by Doppelt (2008) covering the Rogue Basin, are valuable. These also provide projections.

Trends

The most obvious first issue is atmospheric temperature. During the last century the average for the Rogue Basin rose about 1.2 degrees F while Medford from mid to late century rose 1.4 degrees. In Medford, the average maximum and minimum temperatures rose 1.2 and 1.6 degrees respectively. Meanwhile, the number of record low temperature days dropped substantially and that for record high days rose. As gardeners and farmers probably already appreciate, from mid-century to late century, the Medford growing season increased 11.5%, frost free days increased 8% and freeze free days increased 4.6%.

Precipitation, another important variable, exhibited an annual drop in Medford of 1.1% mid to late century while in the Rogue Basin, including higher elevations, it rose nearly 1 inch during the last century. Additionally, during the last century, precipitation patterns have adjusted with rainfall occurring in heavier flood-inducing downpours rather than the kinder gentler rain that replenishes soil moisture. Of great importance locally is snowfall since melting snow provides irrigation water during our dry summers. The trend at Crater Lake has been a drop in snowpack of 25% from the 1930s to this century, while in the Siskiyous of Northern California snowfall has dropped 11% since the 1950s. Medford snowfall also dropped – over 50% between mid and late century. With less snowpack and earlier snowmelt peak river flow is earlier and lower.

Crater Lake

Throughout the west, the wildfire season has expanded some two and a half months since 1970. NOAA’s Regional Data Center shows Oregon is suffering from abnormally dry to drought conditions, with Southwest Oregon experiencing less than 50% ‘normal’ precipitation for the last 6 months. 2013 was the driest year on record for most of Southwest Oregon. Historically, reduced January to May precipitation contributes substantially to the severity of the forthcoming fire season.

Projections

Assuming we do not change our behavior but continue the current gas emission trend, projections indicate an average annual regional temperature rise of over 8 degrees possible by 2075-2085, with summer climbing nearly 12 degrees and August alone possibly 17 degrees. Such temperature increases would be devastating to natural, agricultural, and forestry systems alike.

In terms of precipitation, projections for the region suggest by late century, the summer growing season will be dryer than historically, while winters might be a little wetter with fall and spring changing little. Snowpack accumulation is projected to continue dwindling, possibly to 10% of the historical level by late century. The projection for stream flow is a shift to even earlier in the season with reduced flow, compromising irrigation needs exactly when greatest – in late summer and early fall.

As summers heat up, lower precipitation suggests increased evapotranspiration with severe drought and wildfire. As warming continues and spring arrives earlier, wildfires in Oregon will likely consume between three and five times more land area by mid-century.

These projections are not guesses to be dismissed as mere opinion. They represent simple continuations of the patterns and trends we have been seeing for many decades with projections based on a solid understanding of the physical properties of components of our planet and how they interact. Unfortunately, Mt. Ashland managers should expect a continued dwindling of snowfall.

If we continue ‘business as usual’, our natural and agricultural systems along with our forests and fish populations will likely be devastated. The question to ask ourselves is whether we are prepared to let this happen. Should we let our burning of fossil fuels compromise the livability of this region and this planet for future generations or should we take steps to avoid such an outcome? Only individual commitment and collaborative action will divert the trends.

Area residents wishing to address climate change are invited to join Southern Oregon Climate Action Now –http://socan.info.