U.S. flagAn official website of the United States government
                    Here's how you know **Official websites use .gov**
                            
                            A **.gov** website belongs to an official government organization in the United States.
 **Secure .gov websites use HTTPS**
                            
                            A **lock** (                            
                              A locked padlock                                                      
                            
                            ) or **https://** means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.


Menu Agricultural Research Service
						
                    U.S. DEPARTMENT OF AGRICULTURE
 Southwest Watershed Research Center: Tucson, AZ
 close



    Research

                    Research Projects
                                    Publications
                                    Collaborations
                                    News
                                    Software
                People

                    Staff Listing
                                    Careers


        


                    About SWRCSearch small
                    Search
            
            ARS Home
                                About ARS
                                Contact Us




ARS Home Pacific West Area Tucson, Arizona SWRC Research Publications at this Location





- ARS National Programs
- Search for a scientific manuscript
- Search for a research project
- ARS Software
- Programs and Projects
- Collaborations
- Subjects of Investigation
- Publications

Title:   Author  item
                                            Moran, Maryitem
                                            Keefer, Timothyitem
                                            PAIGE, G. - UNIVERSITY OF WYOMINGitem
                                            Scott, Russell

                                                         - *Russ*item
                                            Emmerich, Williamitem
                                            Cosh, Michaelitem
                                            O'NEILL, P. - NASA-GSFC
  Submitted to: Fourth Conference on Research and Resource Management in the Southwest Deserts
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 3/1/2008
                                    Publication  Date: 5/2/2008
                                    Citation: Moran, M.S., Keefer, T.O., Paige, G.B., Scott, R.L., Emmerich, W.E., Cosh, M.H., O'Neill, P.E. 2008. Partitioning evapotranspiration using diurnal surface temperature variation.  6th Conference on Research and Resources Mgmt. in the Southwestern Desert - Borders, Boundaries and Time Scales, 2-5 May 2006, Tucson, Az., Proc. Published by USGS Sonoran Desert Research Station. 3 p. Interpretive Summary: The encroachment of woody plants in grasslands across the Western U.S. will affect soil water availability by altering the contributions of evaporation (E) and transpiration (T) to total evapotranspiration (ET).  To study this phenomenon, a network of flux stations is in place to measure ET in grass- and shrub-dominated ecosystems throughout the Western U.S.  A method is described and tested here to partition the daily measurements of ET into E and T based on diurnal surface temperature variations of the soil and standard energy balance theory.  The difference between the mid-afternoon and pre-dawn soil surface temperature, termed Apparent Thermal Inertia (IA), was used to identify days when E was negligible, and thus, ET=T.  The method was tested at Walnut Gulch Experimental Watershed in southeast Arizona based on Bowen ratio estimates of ET and continuous measurements of surface temperature with an infrared thermometer (IRT) from 2004-2005, and a second dataset of Bowen ratio, IRT and stem-flow gage measurements in 2003.  Results showed that reasonable estimates of daily T were obtained using infrared thermometer measurements for selected dates.  The next step is to derive a theoretical approach to determine transpiration rates on dates when evaporation cannot be assumed to be zero.
                                Technical Abstract: The encroachment of woody plants in grasslands across the Western U.S. will affect soil water availability by altering the contributions of evaporation (E) and transpiration (T) to total evapotranspiration (ET).  To study this phenomenon, a network of flux stations is in place to measure ET in grass- and shrub-dominated ecosystems throughout the Western U.S.  A method is described and tested here to partition the daily measurements of ET into E and T based on diurnal surface temperature variations of the soil and standard energy balance theory.  The difference between the mid-afternoon and pre-dawn soil surface temperature, termed Apparent Thermal Inertia (IA), was used to identify days when E was negligible, and thus, ET=T.  The method was tested at Walnut Gulch Experimental Watershed in southeast Arizona based on Bowen ratio estimates of ET and continuous measurements of surface temperature with an infrared thermometer (IRT) from 2004-2005, and a second dataset of Bowen ratio, IRT and stem-flow gage measurements in 2003.  Results showed that reasonable estimates of daily T were obtained using infrared thermometer measurements for selected dates.  The next step is to derive a theoretical approach to determine transpiration rates on dates when evaporation cannot be assumed to be zero.


Return to top


Connect with ARS Sign up


ARS Home
                            USDA.gov
                            Plain Writing
                            Policies & Links
                            Civil Rights Statements
                            FOIA
                            Accessibility Statement
                            Privacy Policy
                            Non-Discrimination Statement
                            Quality of Information
                            USA.gov
                            WhiteHouse.gov