Costa (2025) Chill To Spill: Unlocking Yosemite’s Water Flow

Identification

• Journal: UC Merced Undergraduate Research Journal
• Year: 2025
• Date: 2025-12-16
• Authors: T. C. e C. da Costa
• DOI: 10.5070/m418165650

Research Groups

• University of California, Merced (Environmental Engineering faculty, Professor Erin Hestir)

Short Summary

This project investigates how snowmelt, precipitation, and dam operations interact to influence river overflow and water availability in the Upper Merced River watershed. It found that the speed of snowmelt and dam regulation are critical factors in flood risk and water management, often more so than snowpack volume alone.

Objective

• To assess how snowmelt, precipitation, and dam operations jointly influence water availability and flood risks in the Merced River watershed, comparing a dry year (2022) with a wet year (2023).

Study Configuration

• Spatial Scale: Upper Merced River watershed, near Yosemite National Park, California (Hydrologic Unit Code 18040008).
• Temporal Scale: Two water years: 2022 (dry) and 2023 (wet), with specific focus on spring months (March to May).

Methodology and Data

• Models used:
  • ENVI 5.6 (for processing and analyzing Airborne Snow Observatory data, including band math for Snow Water Equivalent differences, visualization of snowmelt rates).
  • Microsoft Excel (for comparative graphs, basic statistical measures like mean, rate of change, and peak values).
• Data sources:
  • Satellite/Remote Sensing: Airborne Snow Observatory (ASO) LiDAR and imaging spectrometry for high-resolution snow depth and Snow Water Equivalent (SWE) data (3 meter resolution).
  • Observation/In-situ:
    • California Data Exchange Center (CDEC) for hourly river flow data (station ID: MST, Merced River near Stevinson).
    • National Oceanic and Atmospheric Administration (NOAA) National Weather Service for archived monthly precipitation records for the Merced area.
    • Merced Irrigation District (MID) and California State Water Resources Control Board for dam operation reports and qualitative release information.

Main Results

• Snow Depth and Melt: In 2022 (dry year), snow accumulation was low and melted almost entirely by early May. In 2023 (wet year), deep, extensive snowpack persisted into mid-May. SWE difference maps showed 2022 experienced sharp, localized, high-intensity snow loss concentrated in mid-elevations, while 2023 exhibited a more gradual, lower-intensity melt across a broader elevation range.
• River Discharge: The Merced River near Stevinson (MST gauge) showed a quick peak in late March 2022 at 3.23 m³/s, dropping to 0.37 m³/s by late May. In contrast, 2023 discharge rapidly rose past 169.9 m³/s in March and remained high into May.
• Precipitation and Dam Operations: March 2023 precipitation (4.36 mm) was more than four times greater than March 2022 (0.82 mm). Average MID dam outflows during spring 2023 ranged from 164.2 to 198.2 m³/s, significantly higher than 2022, which rarely exceeded 28.3 m³/s.
• Flood Risk Factors: Despite greater SWE and precipitation in 2023, the slower melt rate and better-regulated dam releases by MID reduced immediate flood risk. Conversely, 2022's lower snowpack melted rapidly and was less regulated, leading to an early, high-risk flow surge.

Contributions

• This study demonstrates that snowpack volume alone is not the sole determinant of flood risk; the speed of snowmelt and the timing and extent of dam operations are equally critical.
• It highlights the value of integrating high-resolution remote sensing data (ASO SWE) with traditional hydrological observations (CDEC streamflow, NOAA precipitation) and operational data (MID dam releases) to create a simplified yet effective model for water management.
• The findings support the development of more adaptive irrigation planning and early-warning systems, particularly relevant for snowmelt-driven watersheds facing increasing climate variability.

Funding

The research acknowledges the University of California, Merced’s Environmental Engineering faculty for guidance, and the California Data Exchange Center (CDEC), the Airborne Snow Observatory (ASO), NOAA’s National Weather Service, and the Merced Irrigation District (MID) for providing openly accessible data resources. No specific project or program funding was explicitly stated for the research itself.

Citation

@article{Costa2025Chill,
  author = {Costa, T. C. e C. da},
  title = {Chill To Spill: Unlocking Yosemite’s Water Flow},
  journal = {UC Merced Undergraduate Research Journal},
  year = {2025},
  doi = {10.5070/m418165650},
  url = {https://doi.org/10.5070/m418165650}
}