Statistical Modeling of Historical Daily Water Temperatures in the Lower Columbia River

et al. 2023

River Research & Apps

Water temperature is a critical ecological indicator; however, few studies have statistically modeled century‐scale trends in riverine or estuarine water temperature, or their cause. Here, we recover, digitize, and analyze archival temperature measurements from the 1850s onward to investigate how and why water temperatures in the lower Columbia River are changing. To infill data gaps and explore changes, we develop regression models of daily historical Columbia River water temperature using time‐lagged river flow and air temperature as the independent variables. Models were developed for three time periods (mid‐19th, mid‐20th, and early 21st century), using archival and modern measurements (1854–1876; 1938–present). Daily and monthly averaged root‐mean‐square errors overall are 0.89°C and 0.77°C, respectively for the 1938–2018 period. Results suggest that annual averaged water temperature increased by 2.2°C ± 0.2°C since the 1850s, a rate of 1.3°C ± 0.1°C/century. Increased water temperatures are seasonally dependent. An increase of approximately 2.0°C ± 0.2°C/century occurs in the July–Dec time‐frame, while springtime trends are statistically insignificant. Rising temperatures change the probability of exceeding ecologically important thresholds; since the 1850s, the number of days with water temperatures over 20°C increased from ~5 to 60 per year, while the number below 2°C decreased from ~10 to 0 days/per year. Overall, the modern system is warmer, but exhibits less temperature variability. The reservoir system reduces sensitivity to short‐term atmospheric forcing. Statistical experiments within our modeling framework suggest that increased water temperature is driven by warming air temperatures (~29%), altered river flow (~14%), and water resources management (~57%).

Section: Methods and Datamentioning

confidence: 99%

Warming of the lower Columbia River, 1853 to 2018

Scott

et al. 2023

River Research & Apps

“…The deviation from climatology is modeled, and the result is added back to climatology to obtain estimates of T w . A similar approach has also been applied to the Columbia River (Scott, 2020;Scott et al, 2023); other statistical models applied to this region include Moore (1967), Donato (2002), Bottom et al (2011), andMayer (2012). For a generic variable X(t) measured daily, we define the climatological average as…”

Section: Statistical Modelmentioning

confidence: 99%

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

Hydrol. Earth Syst. Sci.

Diefenderfer

2023

Abstract. Using archival research methods, we recovered 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 ∘C per century since the mid-19th century, with the largest shift in January and February (1.3 ∘C per century) and the smallest in May and June (∼ 0.8 ∘C per century). The duration that the river exceeds the ecologically important threshold of 20 ∘C has increased by about 20 d since the 1800s, to about 60 d yr−1. Moreover, cold-water days below 2 ∘C 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 ∘C) but also occur due to alterations in the river system such as depth increases from reservoirs (0.34 ± 0.12 ∘C). Managed release of water affects Tw seasonally, with an average reduction of up to 0.56 ∘C estimated for September. River system changes have decreased variability (σ) in daily minimum Tw by 0.44 ∘C, increased thermal memory, reduced interannual variability, and reduced the response to short-term meteorological forcing (e.g., heat waves). These changes fundamentally alter the response of Tw to climate change, posing additional stressors on fauna.

“…We employ a stochastic modeling approach (e.g., Caissie et al, 1998;Benyaha et al, 2007) in which the dependent variable (water temperature Tw) and the independent variables (air temperature TA and river discharge Q) are decomposed into a long term climatological average and a time varying component. A similar approach has also been applied to the Columbia River (Scott, 2020;Scott et al, 2022). For a generic variable X(t) measured daily, the climatological average is defined as,…”

Section: Statistical Modelmentioning

confidence: 99%

Warming of the Willamette River, 1850–present: the effects of climate change and direct human interventions

Diefenderfer

2022

Preprint

Abstract. 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 °C /century since the mid-19th century, with the largest shift in January/February (1.3 °C /century) and the smallest in May/June (~ 0.8 °C /century). The duration that the river exceeds the ecologically important threshold of 20 °C has increased by ~20 days since the 1800s, to ~60 d yr-1. Moreover, cold water days below 2 °C 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 °C) but also occur due to increased reservoir capacity, altered land use and river morphology, and other anthropogenic changes (0.34 ±0.12 °C). Managed release of water influences Tw seasonally, with an average reduction of 0.27 °C and 0.56 °C estimated for August and September. System changes have decreased daily variability (σ) by 0.44 °C, increased thermal memory, and reduced interannual variability. These system changes fundamentally alter the response of Tw to climate change, posing additional stressors on fauna.