A novel method for frequency analysis of high water temperatures using temperature duration curves in a partially regulated watershed
Bibliographic record
Abstract
Water temperature is the key variable for aquatic environmental assessments, and in the absence of long-term observational records, simulations provide essential data for further environmental analysis. In this study, we investigate the upper percentiles of a novel Temperature Duration Curve (TDC) as a proxy to characterize high water temperatures in a partially regulated watershed. The study area comprises the 47,200 km 2 Nechako Watershed of British Columbia, Canada, where nine hydrometric stations measure streamflow and water temperature. Four sites represent regulated flows, while five sites are unregulated. Using daily streamflow and water temperature observations and ERA5-Land air temperature data, the Air2Stream model was calibrated for historical periods from 1950 to 2023. Simulations were also conducted using naturalized flows for the regulated Nechako River at Vanderhoof and Isle Pierre to reconstruct naturalized water temperatures. A frequency analysis was performed on observed, simulated, and naturalized water temperatures for different return periods and TDC percentiles. The analysis included exceedances of 0, 1, 5, and 10 % for high temperatures and the 50th percentile (median) for mean temperatures. Results showed robust model performance with RMSE <1.5 °C (NSE > 0.9 and KGE > 0.8) for all stations during calibration. The frequency curves showed reduced high temperatures for the Nechako River at Vanderhoof due to ecological flow releases, but increased mean temperatures for return periods >2 years. This novel approach suggests that thermal mandates should be related to Q 5 and Q 10 , which had the best agreement between observations and simulations. The method is applicable globally across various basin sizes and hydrological regimes, making it a valuable tool for assessing water temperature dynamics in diverse environments. • Air2stream yields simulated water temperatures for 5 regulated and 4 natural rivers. • Simulations provide naturalized water temperatures for key Nechako River sites. • Novel water temperature duration curve and frequency curves developed for analysis. • Model performance varies between different quantiles for high water temperatures. • Method gives means to assess climate change and heatwave water temperature impacts.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".