Water Availability Impacts on Evapotranspiration Partitioning

Russell L. Scott, John F. Knowles, Jacob A. Nelson, Pierre Gentine, Xi Li, Greg Barron-Gafford, Ross Bryant, Joel A. Biederman

Research output: Contribution to journalArticlepeer-review

Abstract

Knowing how evapotranspiration (ET) is mediated by abiotic and biotic pathways is essential to understanding how water affects ecosystem productivity. Recent studies have investigated the average transpiration fraction (T/ET) across sites and biomes, but the temporal variability of the partitioning and its controls are less understood. Here, we examine how water availability may regulate the seasonal to interannual variability of ET partitioning. To do this, we leveraged four partitioning techniques and long-term (14 years) eddy-flux records from a semiarid grassland and riparian woodland site in southeastern Arizona USA that share the same climate but differ in water table depth. T/ET was sensitive to changes in water availability over space and time as evidenced by consistently lower and more variable T/ET at the grassland, where the vegetation does not access groundwater. Seasonally, a pronounced dry foresummer T/ET depression at the rainfall-dependent grassland resulted in a bimodal T/ET distribution. In contrast, T/ET was unimodally distributed at the groundwater-dependent woodland, where high T/ET levels were maintained throughout both the dry and wet summer periods. Annual transpiration at both sites closely tracked water availability as quantified by ET, whereas abiotic evaporation was nearly constant. All ET partitioning methods yielded similar patterns of seasonal and interannual T/ET, although they differed by approximately 5 to 10% in magnitude. At both sites, transpiration was most closely correlated to plant metrics (photosynthesis, leaf area index) and ET, whereas evaporation was most correlated to surface moisture variables (soil moisture, precipitation). However, substantial differences between monthly and annual correlations demonstrate variable controls on monthly partitioning throughout the year. These results provide novel insights into the effects of water availability on the seasonal and interannual variability of ET partitioning and illuminate mechanisms regulating terrestrial ecosystem carbon and water exchange.

Original languageEnglish (US)
Article number108251
JournalAgricultural and Forest Meteorology
Volume297
DOIs
StatePublished - Feb 15 2021

Keywords

  • Eddy covariance
  • Grassland
  • Groundwater
  • Productivity
  • Riparian woodland
  • Semiarid
  • Transpiration
  • Water use efficiency

ASJC Scopus subject areas

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

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