Riparian Zone Evapotranspiration Estimates using Streamflow Diel Signals

Abstract:

Diel climate variations impact vegetation and hydrologic systems in semi-arid mountainous watersheds primarily through transpiration. The impact diel variations have are particularly evident in streamflow during low flows. Understanding the controls on streamflow diel signals and the interaction they have within the riparian zone has been a focus of multiple studies to better understand the riparian zones as a system. The focus of the study was to monitor streamflow diel signals at five gauging stations within the same watershed to calculate riparian zone evapotranspiration (ET) and to understand diel signal variability throughout the watershed. Amplitude and timing of diel signals were analyzed at each site and used in determining controls on the diel signal. Meteorological and sap flux measurements were also monitored on both hillslope and riparian areas for comparison of fluxes. A spatially distributed hypsometric method was used to calculate ET for each gauging station sub-watershed for comparison with riparian ET estimates. The study found that, with the use of diel signals and a fixed riparian area, the estimated riparian zone ET ranged from a fraction to several times the calculated meteorological ET depending on the season. Although the riparian zone ET calculation was highly variable, it was constrained using diel signal timing and amplitude. Observations of differences in hillslope and riparian zone meteorological and sap flux variables also supported diel signal calculations. The study concludes that riparian zone ET is a substantial contributor to watershed scale ET during the summer months and that streamflow diel signal plays a large role in understanding watershed scale interactions and the riparian zone’s influence on a semi-arid watershed.