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Title: Ecosystem evapotranspiration: Challenges in measurements, estimates, and modeling

item AMATYA, AMATYA - Us Forest Service (FS)
item IRMAK, SUAT - University Of Nebraska
item Gowda, Prasanna
item SUN, GE - Us Forest Service (FS)

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2016
Publication Date: 4/27/2016
Citation: Amatya, A.M., Irmak, S., Gowda, P., Sun, G. 2016. Ecosystem evapotranspiration: Challenges in measurements, estimates, and modeling. Transactions of the ASABE. 59(2):555-560.

Interpretive Summary: Evapotranspiration is a complex surface energy-balance process. Our current understanding of the magnitude and degree of its interactions with many environmental factors is incomplete. This is an introductory paper of the Special Issue “Evapotranspiration: Challenges in Measurement and Modeling from Leaf to the Landscape Scale and Beyond” published by the Natural Resources and Environmental Systems (NRES) Community of the American Society of Agricultural and Biological Engineering. It presents summary of 12 individual papers published in the special issue and highlights advances in knowledge across four key topics: (1) reference evapotranspiration, (2) evapotranspiration processes and pathways, (3) evapotranspiration modeling, and geospatial technology in estimating evapotranspiration. It also briefly discusses knowledge gaps and potential tools and technologies that are available to fill those knowledge gaps.

Technical Abstract: Evapotranspiration (ET) processes at the leaf-to-landscape scales in multiple land uses have important controls and feedbacks for the local, regional and global climate and water resource systems. Innovative methods, tools, and technologies for improved understanding and quantification of ET and crop water use are critical for adapting more effective management strategies to cope with increasing demand for freshwater resources under global change. This article introduces an ASABE Special Collection of twelve papers on ET monitoring and modeling research for multiple land uses and scales. The Collection focuses on recent advances in four critical topical areas: 1) reference ET (REF-ET) method development and applications, including crop management and irrigation scheduling, limitations due to sensor inaccuracies and variability, and sensitivity to climatic drivers (3 papers); 2) ET process and pathway characterization, including canopy interception, transpiration, and soil evaporation measured using various state-of-the-art techniques on crop lands and plantation forests, and effects of soil moisture on grassland water balance (3 papers); 3) ET simulation within ecohydrological models (SWAT, MIKESHE, RQWQM, RZ-SHAW, RegCM-BATS, DRAINMOD-FOREST, and Thornthwaite Water Balance) as well as related processes , such as crop growth and ET/PET ratios , for grass, crop, and forest lands (4 papers); and 4) geospatial technology applications such as using remote sensing to estimate ET and its components for various land uses (2 papers). Study sites represent a range of spatial scales and ecohydrological settings, including grasslands in Inner Mongolia dry lands in northern China, semiarid high plains in Texas, corn-production regions from Iowa to Colorado, forest plantations on the humid Atlantic Coastal Plain, developed coastal areas of the island of Taiwan, and the continental US. Results from these studies help guide current development and assessment of REF-ET concept and ET and monitoring and modeling of their components, in multiple scales and ecosystems. The studies also set a platform for addressing potential inaccuracies in data from weather sensors or in algorithms used in remote sensing products for estimating ET and its parameters, and uncertainties in REF-ET estimates, for tall forest vegetation in particular. Furthermore, the studies offer insights on the interactions between climatic variability and change and vegetation through the ET process.