February 15, 2024
Journal Article

Warming of the Willamette River, 1850–present: the effects of climate change and river system alterations


Using archival research methods, we found and combined data from multiple sources to produce a unique, 140 year record of daily water temperature (Tw) in the lower Willamette River, Oregon (1881– 1890, 1941– present). Additional daily weather and river flow records from the 1850s onwards are used to develop and validate a statistical regression model of Tw for 1850– 2020. The model simulates the time-lagged response of Tw to air temperature and river flow, and is calibrated for three distinct time periods: the late 19th, mid 20th, and early 21st centuries. Results show that Tw has trended upwards at ~1.1 oC /century since the mid-19th century, with the largest shift in January/February (1.3 oC /century) and the smallest in May/June (~ 0.8 oC /century). The duration that the river exceeds the ecologically important threshold of 20 oC has increased by ~20 days since the 1800s, to ~60 d yr-1. Moreover, cold water days below 2 oC have virtually disappeared, and the river no longer freezes. Since ~1900, changes are primarily correlated with increases in air temperature (Tw increase of 0.81 ±0.25 oC) but also occur due to increased reservoir capacity, altered land use and river morphology, and other anthropogenic changes (0.34 ±0.12 oC). Managed release of water influences Tw seasonally, with an average reduction of 0.27 oC and 0.56 oC estimated for August and September. System changes have decreased daily variability (??) by 0.44 oC, increased thermal memory, and reduced interannual variability. These system changes fundamentally alter the response of Tw to climate change, posing additional stressors on fauna.

Published: February 15, 2024


Talke S.A., D.A. Jay, and H.L. Diefenderfer. 2023. Warming of the Willamette River, 1850–present: the effects of climate change and river system alterations. Hydrology and Earth System Sciences 27, no. 14:2807–2826. PNNL-SA-176975. doi:10.5194/hess-27-2807-2023