Evapotranspiration and surface energy balance of a common reed-dominated riparian system in the platte river Basin, Central Nebraska

Quantifying actual evapotranspiration (ETa) of riparian zones is important for more robust water balance analyses that will enable better planning, managing, and allocating of water resources as well as developing strategies to protect delicate riparian ecosystem functions. The ET_a, sensible heat flux (H), net radiation (R_n), soil heat flux (G), meteorological variables (air temperature, T_a; incoming shortwave radiation, R _s; wind speed, u₃; relative humidity, RH; vapor pressure deficit, VPD; precipitation, etc.), and albedo were measured on an hourly time step, and leaf area index (LAI) and plant height were measured on a weekly basis for a common reed (Phragmites australis) dominated cottonwood (Populus deltoides) and peach-leaf willow (Salix amygdaloides) riparian plant community in 2009 and 2010 through extensive field campaigns conducted in the Platte River basin in central Nebraska. The two growing seasons were contrasted by warmer air temperatures, higher precipitation, and presence of flood water on the surface during the 2010 season. The seasonal variations of daily average ET _a were mainly controlled by R_n and air temperature. In 2009, total ET_a and precipitation were 679 mm and 280 mm, respectively, and the values were substantially greater in 2010 (982 mm and 508 mm, respectively). The seasonal daily ET_a for the mixed plant community ranged from 0.5 to 8.5 mm d^-1 with a seasonal average of 3.7 mm d^-1 in 2009 and from 0.5 to 11 mm d^-1 with a seasonal average of 5.5 mm d^-1 in 2010. In 2010, ET_a varied widely with meteorological conditions and in response to variations in phenology of the vegetation to flooding. In 2009, on a seasonal average basis, a total of 77% and 14% of the available energy was partitioned into ET _a and H, respectively. In 2010, over 90% and -12% (negative due to flooding) of the available energy was partitioned into ET_a and H, respectively. The research results presented here provide valuable ETa data and information for enhancing the understanding of the interactions between the surface/vegetation conditions and the surrounding microclimate and surface energy balance for mixed riparian vegetation. The results of this research should aid water managers and decision/policy makers in accounting for water use rates of phragmites-dominated cottonwood and peach-leaf willow riparian plant communities in water balance analyses to make better-informed water resources planning and management decisions.