What climate trends have we observed locally over the past century? And what do we have to look forward to in the next 50-100 years? The following is a very quick summary of regional climate trends, based partly on information presented at the recent “Rogue Basin Climate Summit” and partly on other published information. Of course, any errors of interpretation and understanding are my own.

What have we seen? Trends 1895-present

Simply put, it’s gotten warmer in the Rogue valley over the past 100+ years. Since 1895 the average temperature has increased by 2.6 F in Ashland and 4.3 F in Grants Pass (see figure below). Medford average temperatures have likewise increased, with the biggest gains occurring since the 1980s.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What about precipitation? Again, there is a lot of year to year variation, but in this case there is no real upward or downward trend.   We have seen major droughts, such as in the 1930s and 1980s, as well as individual very wet and very dry years and longer periods of wetter and cooler climate. At least some of this variability can be attributed to phenomena like El Nino and the Pacific Decadal Oscillation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Old timers in the Rogue Valley talk about days of heavy snows in the valley and those aren’t simply romantic memories. In the early 1900s, Medford averaged 9” of snowfall annually; not much, but with occasional storms dumping a foot or more. Since the 1980s there have been few such large storms and the annual average has decreased to under 4”. Crater Lake snowfall shows huge annual variations but the overall trend has been downward since the 1930s.

So, in sum: it’s gotten warmer, there hasn’t been much change in rainfall, and snowfall has decreased.   Of course, these changes in average values can be hard to discern, because there is so much variability.

If you want to take a look at the data yourself, the University of Washington has a great online tool that allows you to look at temperature and precipitation trends over the past 100 or so years at weather stations all around the northwest. Curious about temperatures in Prospect, or rainfall in Brookings? Snowfall in Bend or Baker? This tool shows a chart of the year to year data and the overall trend. I had a lot of fun playing with it.

What does the future hold?

Probably more of the same: hotter, less snow, not much change in overall precipitation. Average temperatures are predicted to increase 5-9 F by 2100 in the Rogue Valley, depending on the level of greenhouse gas emissions and other factors. Right now we’re on track to hit the higher end of that prediction. So what does that mean? A climate a lot more like Redding’s, according to Phil Mote, Director of the Oregon Climate Service. 2015 is on track to be the warmest year ever in the Rogue Valley (and worldwide, for that matter). And this year will be more like norm in the future.

Another way to look at it is to consider how temperature changes with elevation. Typically for every 1,000 foot gain or loss in elevation we see a 3.5 F change in temperature. So a 7 degree increase (midway between a low and high prediction) is roughly equivalent to a 2,000 foot loss in elevation.   Sites at 3,500 feet would have temperatures like those of the valley floor, all other things equal.

In terms of precipitation, Canada is expected to get wetter, according to Mote, and the SW will be drier. We’re in the middle, so predictions of precipitation are “a wash”, he said. Another speaker stated that the average of current models shows no big change in Rogue valley precipitation, but there may be more winter rainfall and less in the summer.

Snowfall is predicted to decrease, dramatically so at lower elevation sites. The average snow level will likely increase 1,000-2,000’ feet. 2015, with 11% of the historical average snowpack, may be a typical year several decades from now.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

With less snow and earlier melt outs we’re looking at earlier peak flows and lower summer flows, resulting in higher stream temperatures and other water quality issues.

Increases in fire are an obvious concern. Fire season length is on an upward trend in the US west and that trend is likely to continue.   In recent decades we’ve seen an increase in the acres burned and in fire severity in many areas of the US west (due to fuels buildups as well as climate); the predictions for the Rogue Basin are for a 300-400% increase in the area burned by 2100. It’s not good.

 

 

 

 

 

 

 

 

 

 

 

 

Higher temperatures and less summer rain also translate into increases in tree stress and potential losses to insects and abiotic diseases. We’ve seen a large uptick in tree mortality in SW Oregon recently with the dry and hot temperatures but this pales in comparison to the situation in California with its exceptional, extreme drought.

 

 

 

 

 

 

 

 

 

 

 

 

It’s a daunting picture, but there are plenty of things land managers can do to prepare for and adapt to climate changes. For forest owners, the good news is that many of the practices that lead to increased resistance to fire and insect attack, such as thinning, fuels reduction, and promoting drought resistant species, are also practices that will help with climate adaptation. For more information about forests, climate change, and woodland owner strategies, see the OSU Extension Climate and Forests blog.