Prospects of Direct Evapotranspiration Measurements for Immediate Societal Benefits

Continental-scale research infrastructures and flux networks (e.g., AmeriFlux, AsiaFlux, ChinaFlux, ICOS, NEON, OzFlux), as well as numerous smaller GHG flux networks and individual sites are often focused on measuring and modeling carbon dioxide and other GHG exchange between ecosystem and atmosphere. Such measurements require a high-quality measurement of water vapor flux (evapotranspiration, ET) to help correctly compute the GHG exchange, and various soil and plant water measurements to help interpret the results. Effectively, these GHG networks are also ET networks, often with a large set of supporting water measurements. However, beyond the important applications of computing and interpreting ecosystem-level GHG exchange, the water measurements at the GHG flux sites are rarely fully utilized. Improved utilization and expansion of water measurements at GHG flux sites can address a wide range of applications, including: measuring instantaneous water use efficiency, calculating long-term water budgets, investigating turbulent transport theory, informing site-specific process-level studies, and integrating FLUXNET sites with proximal optical and remote sensing measurements for better predictability of ET and carbon-water coupling. Cutting-edge technologies to assess water use on leaf-level to ecosystem-level scales have been actively developed in academia for the past 40 years. One example of such technologies is a next-generation fully-automated evapotranspiration station network, to effectively and efficiently handle the “big data” on water use coming from a grid of measurement stations providing high spatial and temporal coverage of water usage on multiple scales, ranging from a single watershed to a region, state, or a continent. This presentation aims to provide multiple examples and validations against existing standards for the latest technology (hardware and scientific method) behind the eddy covariance approach, allowing for direct, field-scale, unattended, and automated measurements of evapotranspiration.