Osei et al. (2025) An analysis of the long-term trend of evaporative water loss in Lake Hefner (Oklahoma) for sustainable water management

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-11-20
• Authors: Kwabena Osei, G. Thomas LaVanchy
• DOI: 10.1016/j.ejrh.2025.102945

Research Groups

• Department of Geography, Oklahoma State University, Stillwater, OK, USA
• Department of Geography, University of Georgia, Athens, GA, USA

Short Summary

This study analyzed long-term evaporation trends at Lake Hefner, Oklahoma, from 1985 to 2018, revealing a significant increase primarily driven by air temperature, which poses a substantial and unmanaged water loss for municipal supply, largely overlooked in current water management policies.

Objective

• Analyze long-term annual and seasonal evaporation trends at Lake Hefner from 1985 to 2018.
• Identify the dominant climatic drivers influencing reservoir evaporation.
• Quantify the extent to which evaporation contributes to total water loss relative to precipitation, inflows, and storage change.
• Assess how reservoir evaporation is addressed in water management and propose strategies for more adaptive planning.

Study Configuration

• Spatial Scale: Lake Hefner, a medium-sized municipal reservoir (10.1 km² surface area, 92.6 million cubic meters storage capacity) in central Oklahoma, USA, within the Southern Great Plains (SGP) region.
• Temporal Scale: 1985 to 2018 (34 years) for evaporation and climate trends; 2000 to 2018 for water balance analysis.

Methodology and Data

• Models used:
  • Global Lake Evaporation Volume (GLEV) dataset algorithm (Penman combination equation incorporating heat storage changes).
  • Mann-Kendall (MK) trend test.
  • Sen’s Slope estimator.
  • Multiple Linear Regression (MLR) model.
  • Water balance equation: ΔS = P + I − (E + W).
  • Variance-covariance decomposition for interannual variability.
• Data sources:
  • Global Lake Evaporation Volume (GLEV) dataset (Zhao et al., 2022) for monthly evaporation and lake area.
  • NASA POWER (Prediction of Worldwide Energy Resources) for daily meteorological variables (air temperature, wind speed, solar radiation, relative humidity) (1985–2018).
  • Oklahoma Mesonet station data (Spencer, SPEN;87) for meteorological data (2000–2018) and precipitation.
  • United States Geological Survey (USGS) for reservoir storage and canal inflows (monitoring stations 07240000 and 07159550).
  • City of Oklahoma City for municipal withdrawals.
  • NOAA National Centers for Environmental Information (NCEI) for long-term precipitation data.
  • U.S. Drought Monitor (USDM) for drought severity data.
  • Conservation reports and water management policies from the Oklahoma Water Resources Board (OWRB) and the Oklahoma City Water Utilities Trust (OCWUT).

Main Results

• Evaporation at Lake Hefner increased significantly by +0.113 mm yr⁻¹ (p < 0.05) over the 34-year period (1985–2018), with cumulative losses reaching 3.84 mm.
• The most pronounced evaporation increases occurred in autumn and winter, suggesting shifts in seasonal evaporative patterns.
• Air temperature was identified as the dominant climatic driver of these evaporation changes.
• On average, evaporation removed approximately 13.0 million cubic meters (MCM) per year, representing about 19.1 % of total annual outflows.
• Cumulatively, nearly 440 MCM of water was lost to evaporation over the 34-year study period.
• During dry years, evaporation's proportional contribution to total water inputs increased markedly from 17.7 % (wet years) to 25.9 %.
• Despite its significance, evaporation monitoring and forecasting are largely absent in current reservoir operations and broader state-level water policy (e.g., Oklahoma Comprehensive Water Plan).
• The water balance model showed strong agreement (R² = 0.96) between computed and observed annual changes in storage.
• Canal inflow accounted for the majority (~69 %) of interannual storage variability, while evaporation contributed less than 1 %.

Contributions

• Provides a multi-decadal analysis of evaporation dynamics for a medium-sized reservoir, a scale often understudied compared to large reservoirs or short-term pan studies.
• Integrates climatic drivers with a water balance framework, allowing attribution of evaporation changes to both meteorological forcing and reservoir-scale hydrology.
• Explicitly links physical evaporation processes to reservoir operations and state water policy, highlighting evaporation as an overlooked but management-relevant water loss.
• Offers the first modern reassessment of evaporation at Lake Hefner under contemporary climatic and governance conditions, building upon its historical role as a benchmark site for evaporation research.
• Provides transferable lessons for reservoir sustainability across the Southern Plains and semi-arid regions globally due to Lake Hefner's representative characteristics and climate-driven evaporation.

Funding

• Not explicitly stated in the provided text.

Citation

@article{Osei2025analysis,
  author = {Osei, Kwabena and LaVanchy, G. Thomas},
  title = {An analysis of the long-term trend of evaporative water loss in Lake Hefner (Oklahoma) for sustainable water management},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.102945},
  url = {https://doi.org/10.1016/j.ejrh.2025.102945}
}