Evapotranspiration of Hawai‘i Final Report Thomas W. Giambelluca1, Xiufu Shuai1, Mallory L. Barnes2, Randall J. Alliss3, Ryan J. Longman1, Tomoaki Miura2, Qi Chen1, Abby G. Frazier1, Ryan G. Mudd1, Lan Cuo4, and Aaron D. Businger1 1 , Honolulu, HI, USA; 2Department of Natural Resources and Environmental Managment, University of Department of ,Geography, Honolulu, HI, University USA; 3Northrop of Hawai‘i Grumman at Mānoa Corporation, Chantilly, VA, USA; 4Institute for Tibetan Plateau Research, Chinese Academy of Sciences, Hawai‘i at Mānoa Beijing, China Submitted to U.S. Army Corps of Engineers – Honolulu District and Commission on Water Resource Management, State of Hawai‘i February 2014 EVAPOTRANSPIRATION OF HAWAI‘I FINAL REPORT Acknowledgements The Hawai‘i Evapotranspiration Project was conducted under an agreement between the State of Hawai‘i Commission on Water Resource Management and the U.S. Army Corps of Engineers, Honolulu District under Section 22 of the Water Resources Act of 1974. Written Agreement No. W9128A-08-D-0007 between the U.S. Army Corps of Engineers and CH2M Hill, Inc., included a task subcontracted to the Department of Geography, University of Hawai‘i to develop evapotranspiration maps for the State of Hawai‘i. This project was facilitated through the assistance of numerous individuals and organizations. Please see the “People” tab of the Evapotranspiration of Hawai‘i web site for information about those who contributed to this work. We are grateful to those listed there, as well as many other individuals who contributed to Hawai‘i’s climate dataset by making and recording measurements and maintaining the data. We thank Brett Holben and his staff for establishing and maintaining the two AeroNet sites used in this study, Christian Gueymard for providing us with an updated version of the REST2 model and for assistance in quantifying model input variables specific to Hawaii, Robert Evans of the National Oceanic and Atmospheric Administration (NOAA) for the ozone values required for the REST2 model, Jesse Acosta of the State of Hawai‘i Division of Forestry and Wildlife for helping to maintain the RAWS network in Hawai‘i, the Western Regional Climate Center for providing access to the RAWS climate database, and the National Renewable Energy Laboratory (NREL) Measurement and Instrument Data center (MDIC) for the use of their solar data. We are grateful to Chunxi Zhang of the International Pacific ii EVAPOTRANSPIRATION OF HAWAI‘I FINAL REPORT Research Center , for providing his 1-km albedo analysis of Hawai‘i., University We thank of Lloyd Hawai‘i Hihara at Mānoaand Ryan Sugamoto for providing leaf wetness data obtained under the Pacific Rim Environmental Degradation of Materials Research Program, sponsored by the U.S. Army RDECOM-ARDEC, and the Atmospheric Corrosion Research in Hawai‘i Microclimates project, sponsored by Mandaree Enterprise Corporation and the Office of the U.S. Undersecretary of Defense. We acknowledge support for the development of digital air temperature and relative humidity maps conducted under the Pacific Rim Corrosion Research Program (Lloyd Hihara, PI), funded by the U.S. Department of Defense. We also thank Ray Anderson, of the U.S.D.A. Agricultural Research Service, Riverside, CA, and his colleagues for providing eddy covariance measurements of ET from the Hawai‘i Commercial and Sugar Company plantation on Maui. Lastly, we thank Delwyn Oki, John Engott, Adam Johnson, and Maoya Bassiouni of the Pacific Island Water Science Center, U.S. Geological Survey, Neal Fujii, Commission on Water Resource Management, State of Hawai‘i, and Debbie Solis and Michael Wong, U.S. Army Corps of Engineers, Honolulu District, for providing highly valuable comments and suggestions on a draft version of this report. iii EVAPOTRANSPIRATION OF HAWAI‘I FINAL REPORT Table of Contents Acknowledgements .................................................................................................................. ii List of Figures ............................................................................................................................ vi List of Tables ............................................................................................................................. ix INTRODUCTION ......................................................................................................................... 1 METHODS .................................................................................................................................... 2 Datasets .................................................................................................................................................. 2 Meteorological Data ...................................................................................................................................... 3 Cloud Cover Data ............................................................................................................................................ 5 Land Cover Characteristics ........................................................................................................................ 5 Base Periods of Data Used in Model Development and Validation ........................................... 9 Available Energy .............................................................................................................................. 10 Net Radiation ................................................................................................................................................ 10 Solar Radiation ................................................................................................................................. 10 Clear-sky Solar Radiation Model ........................................................................................................... 11 Cloud Frequency Analysis ....................................................................................................................... 13 Direct and Diffuse Radiation .................................................................................................................. 18 Terrain Shading ........................................................................................................................................... 19 Reflected Shortwave Radiation .................................................................................................. 19 Downward Longwave Radiation ................................................................................................ 21 Upward Longwave Radiation ...................................................................................................... 22 Energy Storage Fluxes .................................................................................................................... 22 Soil Heat Flux ................................................................................................................................................ 22 Biomass and Air Layer Energy Storage .............................................................................................. 23 Other Meteorological Variables ................................................................................................. 24 Air temperature ........................................................................................................................................... 24 Relative Humidity ....................................................................................................................................... 27 Wind Speed .................................................................................................................................................... 28 Potential Evapotranspiration ..................................................................................................... 30 Priestley-Taylor Potential Evapotranspiration .............................................................................. 30 Penman-Monteith Potential Evapotranspiration .......................................................................... 31 Grass Reference Surface Potential Evapotranspiration .............................................................. 34 Evapotranspiration ......................................................................................................................... 34 Wet-canopy Evaporation ......................................................................................................................... 35 Transpiration ................................................................................................................................................ 36 Soil Evaporation .......................................................................................................................................... 40 RESULTS .................................................................................................................................... 42 Land Surface Characteristics ....................................................................................................... 42 Leaf Area Index ............................................................................................................................................ 42 Vegetation Cover Fraction ....................................................................................................................... 43 Vegetation Height .......................................................................................................................................