Using Median Point in Keeling Plot to Reduce the Uncertainty of the Isotopic Composition of Evapotranspiration
[1];
- a Center for Agricultural Water Research in China, China Agricultural University, Beijing, China, b Department of Earth and Environmental Sciences, Indiana University Indianapolis, Indianapolis, Indiana, c Department of Plant and Environmental Sciences, New Mexico State University, Las Cruces, New Mexico, d Department of Environmental Sciences, University of California Riverside, California
- b Department of Earth and Environmental Sciences, Indiana University Indianapolis, Indianapolis, Indiana
- e Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, Guangdong, China
- d Department of Environmental Sciences, University of California Riverside, California
- f Department of Mathematical Sciences, Indiana University Indianapolis, Indianapolis, Indiana
- a Center for Agricultural Water Research in China, China Agricultural University, Beijing, China
Abstract The isotopic composition of evapotranspiration δ ET is a crucial parameter in isotope-based evapotranspiration (ET) partitioning and moisture recycling studies. The Keeling plot method is the most prevalent method to calculate δ ET , though it contains large extrapolated uncertainties from the least squares regression. Traditional Keeling regression uses the mean point of individual measurements. Here, a modified Keeling plot framework was proposed using the median point of individual measurements. We tested the δ ET uncertainty using the mean point [ σ ET (mean)] and median point [ σ ET (median)]. Multiple resolutions of input and output data from six independent sites were used to test the performance of the two methods. The σ ET (mean) would be greater than σ ET (median) when the mean value of inverse vapor concentration ( ) is greater than the median value of inverse vapor concentration [ ]. When applying the filter of r 2 > 0.8, around 70% of σ ET (mean) was greater than σ ET (median). This phenomenon might be due to the normality of the vapor concentration C υ producing the asymmetric distribution of 1/ C υ . The median method could perform significantly better than the mean method when inputting high-resolution measurements (e.g., 1 Hz) and when the water vapor concentration C υ is relatively low. Compared to the mean method, applying the median method could on average reduce 6.88% of ET partitioning uncertainties and could on average reduce 9.00% of moisture recycling uncertainties. This study provided a new insight of the Keeling plot method and emphasized handling model output uncertainty from multiple perspectives instead of only from input parameters.
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- SC0024297
- OSTI ID:
- 2339673
- Journal Information:
- Journal of Hydrometeorology, Journal Name: Journal of Hydrometeorology Journal Issue: 4 Vol. 25; ISSN 1525-755X
- Publisher:
- American Meteorological SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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