STREAM TEMPERATURE INCREASES AND LAND-USE IN A FORESTED OREGON WATERSHED

The Salmon Creek Watershed drains 325 km**2 of forested terrain in the Cascade Mountains of western Oregon. Over a 30-year period average daily maximum and minimum stream temperatures, calculated from the 10 warmest days of each year, have risen 6 degree C and 2 degree C, respectively. In contrast, a small decrease in maximum air temperatures was found over the same period. Regression analysis indicated a highly significant relationship between a cumulative index of forest harvesting and maximum stream temperatures. Maximum temperatures also tended to increase for several years following major peak flow events. The interaction between harvest activity, changing forest and riparian management practices and the occurrence of natural hydrologic events tend to obscure specific cause-and-effect relationships regarding long-term changes in maximum stream temperature.