Vegetation controls on surface heat flux partitioning, and land-atmosphere coupling

• Published in: Geophysical research letters Vol. 42; no. 21; pp. 9416 - 9424
• Main Authors: Williams, Ian N., Torn, Margaret S.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 16.11.2015; John Wiley & Sons, Inc; American Geophysical Union
• Subjects: Area; Atmosphere; Atmospheric forcing; Atmospherics; Climate; Constraints; convective triggering; Correlation; Coupling; Evaporation; Evaporative; evaporative fraction; evapotranspiration; Fluctuations; Flux; GEOSCIENCES; Heat; Heat flux; Heat transfer; Humid climates; Hydrologic cycle; Hydrological cycle; Hydrology; land-atmosphere coupling; Latent heat; Latent heat flux; Leaf area; Leaf area index; Leaves; Loads (forces); Measurement; Meteorology; Moisture; Nonlinearity; Partitioning; Phenology; Plains; Semiarid environments; Sensible and latent heat; Sensible and latent heat flux; Soil; Soil moisture; Soils; Transpiration; Vegetation; United States > US; USA, Great Plains; USA
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2015GL066305

We provide observational evidence that land‐atmosphere coupling is underestimated by a conventional metric defined by the correlation between soil moisture and surface evaporative fraction (latent heat flux normalized by the sum of sensible and latent heat flux). Land‐atmosphere coupling is 3 times stronger when using leaf area index as a correlate of evaporative fraction instead of soil moisture, in the Southern Great Plains. The role of vegetation was confirmed using adjacent flux measurement sites having identical atmospheric forcing but different vegetation phenology. Transpiration makes the relationship between evaporative fraction and soil moisture nonlinear and gives the appearance of weak coupling when using linear soil moisture metrics. Regions of substantial coupling extend to semiarid and humid continental climates across the United States, in terms of correlations between vegetation metrics and evaporative fraction. The hydrological cycle is more tightly constrained by the land surface than previously inferred from soil moisture. Key Points Evaporative fraction is often better correlated with vegetation phenology than with soil moisture Vegetation controls on evaporative fraction can be separated from atmospheric forcing Vegetation metrics imply stronger land‐atmosphere coupling than soil moisture metrics