Towards affordable wetland evapotranspiration monitoring using the Variance-Bowen Ratio method: Insights from three contrasting wetlands
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Abstract
Accurate measurement of evapotranspiration (ET) is essential for sustainable water management. Standard methods such as eddy covariance (EC) are costly, while alternatives such as surface renewal are cheaper but require calibration and complex data processing. This study evaluates the utility of the Variance-Bowen Ratio (VBR) method for estimating ET across three California’s wetlands. Using data from 2023, half-hourly latent heat flux (λE) and daily/monthly ET from VBR were compared with EC at one non-tidal (site A) and two tidal (sites B and C) wetlands. λEVBR consistently underestimated λEEC, with root mean squared errors (RMSE) of 61.2 W m-2 at sites A, 106.1 W m-2 at site B, and 137.2 W m-2 at site C, largely due to storage fluxes across sites. Temporal integration improved VBR’s performance at tidal sites, where compensating water heat storage errors yielded low daily and monthly biases (site B: RMSE = 0.78 mm/d and 12 mm/month; r = 0.93; site C: RMSE = 0.90 mm/d and 13 mm/month; r = 0.93), with reduced major axis (RMA) regression slopes of 0.98 and ~0.91. In contrast, biomass heat storage at site A caused persistent biases (RMSEs = 0.97 mm/d and 23 mm/month; daily and monthly RMA slopes ~0.75; r = 0.85). These results highlight VBR’s limitations in environments with substantial storage fluxes. Despite this, VBR is cost-effective for estimating daily and monthly ET, with sensor costs at least tenfold lower than EC and simpler setup, making it suitable for ET monitoring in resource-limited and hard-to-access regions.
Suggested Citation
Wang, T., Senay, G.B., Verfaille, J., Szutu, D.J., Friedrichs, M., Eggleston, J., and Baldocchi, D., 2026, Towards affordable wetland evapotranspiration monitoring using the Variance-Bowen Ratio method: Insights from three contrasting wetlands: Water Resources Research, v. 62, no. 4, e2025WR041365, 18 p., https://doi.org/10.1029/2025WR041365.
ISSN: 1944-7973 (online)
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Towards affordable wetland evapotranspiration monitoring using the Variance-Bowen Ratio method: Insights from three contrasting wetlands |
| Series title | Water Resources Research |
| DOI | 10.1029/2025WR041365 |
| Volume | 62 |
| Issue | 4 |
| Publication Date | April 07, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | American Geophysical Union |
| Contributing office(s) | Earth Resources Observation and Science (EROS) Center |
| Description | e2025WR041365, 18 p. |
| Country | United States |
| State | California |
| Other Geospatial | Sacramento-San Joaquin Delta |