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Estimating Canopy-Scale Evapotranspiration from Localized Sap Flow Measurements

by and *
Department of Natural Resources Management & Environmental Sciences, College of Agriculture, Food & Environmental Sciences, California Polytechnic State University, San Luis Obispo, CA 93407, USA
Author to whom correspondence should be addressed.
Current affiliation: US Geological Survey, California Water Science Center, Santa Maria Field Office, Santa Maria, CA, 93455, USA.
Academic Editors: Luis Garrote and Alban Kuriqi
Water 2022, 14(11), 1812;
Received: 22 April 2022 / Revised: 30 May 2022 / Accepted: 30 May 2022 / Published: 4 June 2022
(This article belongs to the Topic Water Management in the Era of Climatic Change)
The results reported in this work are based in part on measurements of sap flow in a few select trees on a representative riparian forest plot coupled with a forest-wide randomized sampling of tree sapwood area in a watershed located along the Pacific coast in Santa Cruz County, California. These measurements were upscaled to estimate evapotranspiration (ET) across the forest and to quantify groundwater usage by dominant phreatophyte vegetation. Canopy cover in the study area is dominated by red alder (Alnus rubra) and arroyo willow (Salix lasiolepis), deciduous phreatophyte trees from which a small sample was selected for instrumentation with sap flow sensors on a single forest plot. These localized sap flow measurements were then upscaled to the entire riparian forest to estimate forest ET using data from a survey of sapwood area on six plots scattered randomly across the entire forest. The estimated canopy-scale ET was compared to reference ET and NDVI based estimates. The results show positive correlation between sap flow based estimates and those of the other two methods, though over the winter months, sap flow-based ET values were found to significantly underestimate ET as predicted by the other two methods. The results illustrate the importance of ground-based measurements of sap flow for calibrating satellite based methods and for providing site-specific estimates and to better characterize the ET forcing in groundwater flow models. View Full-Text
Keywords: evapotranspiration; sapflow; phreatophyte; riparian; groundwater evapotranspiration; sapflow; phreatophyte; riparian; groundwater
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MDPI and ACS Style

Solum, J.; Malama, B. Estimating Canopy-Scale Evapotranspiration from Localized Sap Flow Measurements. Water 2022, 14, 1812.

AMA Style

Solum J, Malama B. Estimating Canopy-Scale Evapotranspiration from Localized Sap Flow Measurements. Water. 2022; 14(11):1812.

Chicago/Turabian Style

Solum, James, and Bwalya Malama. 2022. "Estimating Canopy-Scale Evapotranspiration from Localized Sap Flow Measurements" Water 14, no. 11: 1812.

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