On the temporal upscaling of evapotranspiration from instantaneous remote sensing measurements to 8-day mean daily-sums

Youngryel Ryu, Dennis D. Baldocchi, T. Andrew Black, Matteo Detto, Beverly E. Law, Ray Leuning, Akira Miyata, Markus Reichstein, Rodrigo Vargas, Christof Ammann, Jason Beringer, Lawrence B. Flanagan, Lianhong Gu, Lindsay B. Hutley, Joon Kim, Harry McCaughey, Eddy J. Moors, Serge Rambal, Timo Vesala

Research output: Contribution to journalArticlepeer-review

115 Scopus citations

Abstract

The regular monitoring of evapotranspiration from satellites has been limited because of discontinuous temporal coverage, resulting in snapshots at a particular point in space and time. We developed a temporal upscaling scheme using satellite-derived instantaneous estimates of evapotranspiration to produce a daily-sum evapotranspiration averaged over an 8-day interval. We tested this scheme against measured evapotranspiration data from 34 eddy covariance flux towers covering seven plant functional types from boreal to tropical climatic zones. We found that the ratio of a half-hourly-sum of potential solar radiation (extraterrestrial solar irradiance on a plane parallel to the Earth's surface) between 10:00hh and 14:00hh to a daily-sum of potential solar radiation provides a robust scaling factor to convert a half-hourly measured evapotranspiration to an estimate of a daily-sum; the estimated and measured daily sum evapotranspiration showed strong linear relation (r2=0.92) and small bias (-2.7%). By comparison, assuming a constant evaporative fraction (the ratio of evapotranspiration to available energy) during the daytime, although commonly used for temporal upscaling, caused 13% underestimation of evapotranspiration on an annual scale. The proposed temporal upscaling scheme requires only latitude, longitude and time as input. Thus it will be useful for developing continuous evapotranspiration estimates in space and time, which will improve continuous monitoring of hydrological cycle from local to global scales.

Original languageEnglish (US)
Pages (from-to)212-222
Number of pages11
JournalAgricultural and Forest Meteorology
Volume152
Issue number1
DOIs
StatePublished - Jan 15 2012
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Forestry
  • Global and Planetary Change
  • Agronomy and Crop Science
  • Atmospheric Science

Keywords

  • Eddy covariance
  • Evapotranspiration
  • FLUXNET
  • MODIS
  • Temporal upscaling

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