Setting the Scene
The Rogue Valley, also known as the Bear Creek watershed, is located in the upper Rogue River basin in southwestern Oregon. The area has been a center for lumber and agriculture. It is also famous for its great weather and easy access to camping, hiking, and fishing. In the last 20 years, the area's population has grown by over 20 percent. Over 200,000 people now live in the 30- by 10-mile Bear Creek valley; another 60,000 (a 30 percent increase) are expected to arrive in the next 30 years.
The watershed ranges in elevation from nearly 1,075 feet at the confluence with the Rogue River to just over 7,500 feet atop Mt. Ashland. The mountains and a relatively deep valley keep out winds, resulting in moist, cold air settling to the bottom. Gain a little altitude anywhere in the valley and the mists clear up. The temperature at higher altitudes can be warmer than at lower altitudes when this condition occurs. This is known as a temperature inversion. When a high pressure system sits over the valley for a week or so, the colder air drains down into the valley, particularly during the long winter nights. The main problem with inversion layers is they also trap polluted air.
In summer, the main pollutant in Jackson County is ozone. In winter, the air in Medford can be worse than any other time of the year due to the burning of woodstoves and fireplaces, especially during periods of air stagnation. Jackson County Public Health's Climate and Health Action Plan lists a significant future climate-related health risk being an increase in air pollution. The future projections of hotter, drier summers and decreasing snowfall will lead to longer allergy and fire seasons with higher risk of more frequent wildfire smoke affecting the valley residents.
Up to 70-95 percent of wildfire smoke particles are thought to be made up of the more dangerous fine particles less than 2.5 micrometers in diameter (PM 2.5).