TY - JOUR
T1 - Evapotranspiration and energy balance of native wet montane cloud forest in Hawai'i
AU - Giambelluca, Thomas W.
AU - Martin, Roberta E.
AU - Asner, Gregory P.
AU - Huang, Maoyi
AU - Mudd, Ryan G.
AU - Nullet, Michael A.
AU - DeLay, John K.
AU - Foote, David
N1 - Funding Information:
This study was made possible through the assistance of many individuals and organizations. The authors especially wish to thank Toby Vana, Harry Buscher, Kim Carlson, Melissa Kunz, Robert Smith, Nick Shema, David Okita, Jon Maka‘ike, Robert Mattos, Todd Tobeck, Tim Tunison, Paul Keali‘iho‘omalu, Michele Montgomery, Patrick Niemeyer, Joseph Conner, and Wanda Martin. We are deeply grateful to Hawai‘i Volcanoes National Park for permitting us to establish the study site within a pristine native forest community in the park. We are grateful to Asko Noormets for allowing us access to his processing code. Special thanks goes to Ed Swiatek (Campbell Scientific Inc.) for his technical advice on tower instrumentation. This project is supported under a collaborative facilities agreement between the Institute of Pacific Islands Forestry (US Forest Service) and the Carnegie Institution of Washington. This paper is based upon work supported by the National Science Foundation under Grant No. EAR-0309731, the endowment of the Carnegie Institution, and by the USGS Biological Resources Discipline Global Change Research Program.
PY - 2009/2
Y1 - 2009/2
N2 - Evapotranspiration (ET) and energy balance were observed, using eddy covariance and other micrometeorological measurements, at a native Metrosideros polymorpha forest site in Hawai'i. Total rainfall for the 12-month study period (2401 mm) was close to the long-term mean (2500 mm year-1), but was highly variable from month to month with distinct dry periods in February, May, and December 2005. Measured annual ET of 996 mm year-1 was slightly higher than previous estimates for similar locations in Hawai'i. However, the energy closure ratio was 0.784, leading us to adjust turbulent energy fluxes upward by 27.6%. The resulting adjusted annual ET of 1232 mm is significantly higher than previous forest ET estimates for Hawai'i. Variations in canopy conductivity suggest that midday stomatal closure is occurring and/or that evaporation is high in the morning because of frequent wet canopy conditions early in the day. The daily fraction of turbulent energy flux used for ET was observed to be lower for days with high net radiation, indicating that transpiration is being limited under conditions of high evaporative demand. ET was generally higher during rainy periods than dry periods. After controlling for differences in available energy, ET is, on average, 29% higher on days with rain than days without rain. The fraction of energy used for ET follows a distinct annual pattern, roughly corresponding to the observed cycle in leaf area at the site, with a minimum in mid-April and a maximum in mid-October. Variations in rainfall appear to be the cause of deviations from the annual cycle of the fraction of energy used for ET. This suggests that ET is strongly controlled by variations in canopy wetness at this wet forest site.
AB - Evapotranspiration (ET) and energy balance were observed, using eddy covariance and other micrometeorological measurements, at a native Metrosideros polymorpha forest site in Hawai'i. Total rainfall for the 12-month study period (2401 mm) was close to the long-term mean (2500 mm year-1), but was highly variable from month to month with distinct dry periods in February, May, and December 2005. Measured annual ET of 996 mm year-1 was slightly higher than previous estimates for similar locations in Hawai'i. However, the energy closure ratio was 0.784, leading us to adjust turbulent energy fluxes upward by 27.6%. The resulting adjusted annual ET of 1232 mm is significantly higher than previous forest ET estimates for Hawai'i. Variations in canopy conductivity suggest that midday stomatal closure is occurring and/or that evaporation is high in the morning because of frequent wet canopy conditions early in the day. The daily fraction of turbulent energy flux used for ET was observed to be lower for days with high net radiation, indicating that transpiration is being limited under conditions of high evaporative demand. ET was generally higher during rainy periods than dry periods. After controlling for differences in available energy, ET is, on average, 29% higher on days with rain than days without rain. The fraction of energy used for ET follows a distinct annual pattern, roughly corresponding to the observed cycle in leaf area at the site, with a minimum in mid-April and a maximum in mid-October. Variations in rainfall appear to be the cause of deviations from the annual cycle of the fraction of energy used for ET. This suggests that ET is strongly controlled by variations in canopy wetness at this wet forest site.
KW - Energy balance
KW - Evapotranspiration
KW - Forest hydrology
KW - Hawai'i Volcanoes National Park
KW - Throughfall
KW - Tropical montane cloud forests
UR - http://www.scopus.com/inward/record.url?scp=57849105011&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=57849105011&partnerID=8YFLogxK
U2 - 10.1016/j.agrformet.2008.08.004
DO - 10.1016/j.agrformet.2008.08.004
M3 - Article
AN - SCOPUS:57849105011
SN - 0168-1923
VL - 149
SP - 230
EP - 243
JO - Agricultural and Forest Meteorology
JF - Agricultural and Forest Meteorology
IS - 2
ER -