The impact of expanding flooded land area on the annual evaporation of rice

Dennis Baldocchi, Sara Knox, Iryna Dronova, Joe Verfaillie, Patty Oikawa, Cove Sturtevant, Jaclyn Hatala Matthes, Matteo Detto

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

Abstract

The amount of published data on annual evaporation on rice remains extremely limited despite the role of rice as a key food source. We report on six years of rice evaporation measurements, based on the eddy covariance method. This rice was cultivated in the hot dry climate of California, where water is a scarce and precious resource. During the first year, we found that rice evaporation exceeded potential evaporation rates and summed to 1155 mm y-1. In following years, we found that annual evaporation decreased yearly, yielding a 15% reduction (to 982 mm y-1) by the sixth year. The remainder of the paper examined the how and why of this unexpected decreasing trend in annual evaporation occurred.We inspected trends in variations in biophysical variables (net radiation, temperature, leaf area index) associated with evaporation and potential biases in the flux measurements using energy balance closure and co-spectral analysis. None of the biophysical variables varied enough to explain this observation. What did change was the area of rice, and nearby flooded wetlands. During the first year, the flooded rice field was less than 1 km2 in area and was relatively isolated. This situation promoted an 'oasis effect' that enabled warm dry air to be entrained from across the top of the planetary boundary layer; this contention was supported by the co-spectral analysis and analysis with a coupled surface energy balance-planetary boundary layer model. By the sixth year of this project, the area of flooded rice and wetlands approached 6 km2, a horizontal scale that seemed to inhibit the 'oasis effect'. We conclude that the amount of water used, on an area basis, by wetland restoration projects will depend upon the spatial extent of these projects.

Original languageEnglish (US)
Pages (from-to)181-193
Number of pages13
JournalAgricultural and Forest Meteorology
Volume223
DOIs
StatePublished - Jun 15 2016
Externally publishedYes

All Science Journal Classification (ASJC) codes

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

Keywords

  • Advection
  • Biosphere-Atmosphere interactions
  • Eddy covariance. AmeriFlux
  • Evaporation
  • Land use and land management
  • Micrometeorology
  • Oasis effect
  • Scale emergent property

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