An overview of an experiment in which 8 different methods of estimating actual evaporation and transpiration were compared using a common database. Methods based on field data, hydrological models, and satellite data were used and the objectives were to compare results and to assess the utility of each method for various applications.
Evapotranspiration - An Overview contains recent advances in the physics of evaporation and transpiration from a typical experimental site to large scale areas. It incorporates many years of authors experience with the latest research on the methods and the models used worldwide, engaging advanced technology and modern instrumentation. The reader benefits from the in-depth analysis and the diverse sites and settings, where the models, applications and methods are tested. Weather conditions, soil moisture, geology, climatic systems are examined for their role and influence on the theoretical and actual water demand by the atmosphere in the earth's ecosystem. This book not only provides students and scientists with the information to improve the procedures for estimating evapotranspiration, but will also help them to manage and evaluate the observed data.
Evapotranspiration (ET) is a critical component of the water and energy balances, and the number of remote sensing-based ET products and estimation methods has increased in recent years. Various aspects of remote sensing of ET are reported in the 11 papers published in this book. The major research areas covered by this book include inter-comparison and performance evaluation of widely used one- and two-source energy balance models, a new dual-source model (Soil Plant Atmosphere and Remote Sensing Evapotranspiration, SPARSE), and a process-based model (ETMonitor); assessment of multi-source (e.g., remote sensing, reanalysis, and land surface model) ET products; development or improvement of data fusion frameworks to predict continuous daily ET at a high spatial resolution (field-scale or 30 m) by fusing the advanced spaceborne thermal emission reflectance radiometer (ASTER), the moderate resolution imaging spectroradiometer (MODIS), and Landsat data; and investigating uncertainties in ET estimates using an ET ensemble composed of several land surface models and diagnostic datasets. The effects of the differences between ET products on water resources and ecosystem management were also investigated. More accurate ET estimates and improved understanding of remotely sensed ET products are crucial for maximizing crop productivity while minimizing water losses and management costs.
The focus of this work is the development of models to estimate evapotranspiration (ET), investigating the partitioning between soil evaporation and plant transpiration at field and regional scales, and calculating ET over heterogeneous vegetated surfaces. Different algorithms with varying complexities as well as spatial and temporal resolutions are developed to estimate evapotranspiration from different data inputs. The author proposes a novel approach to estimate ET from remote sensing by exploiting the linkage between water and carbon cycles. At the field scale, a hybrid dual source model (H-D model) is proposed. It is verified with field observations over four different ecosystems and coupled with a soil water and heat transfer model, to simulate water and heat transfer in the soil-plant-atmosphere continuum. At the regional scale, a hybrid dual source scheme and trapezoid framework based ET model (HTEM), using remote sensing images is developed. This model is verified with data from the USA and China and the impact of agricultural water-saving on ET of different land use types is analyzed, in these chapters. The author discusses the potential of using a remote sensing ET model in the real management of water resources in a large irrigation district. This work would be of particular interest to any hydrologist or micro-meteorologist who works on ET estimation and it will also appeal to the ecologist who works on the coupled water and carbon cycles. Land evapotranspiration is an important research topic in hydrology, meteorology, ecology and agricultural sciences. Dr. Yuting Yang works at the CSIRO Land and Water, Canberra, Australia.
Evapotranspiration (ET) is the combination of transpiration from plants and evaporation from land surface sources of water. Accurate accounting of actual crop ET is critical in agricultural water management, especially in areas with intensive irrigation. Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) is a useful tool to spatially estimate actual evapotranspiration (ETa) using satellite imagery. Although METRIC has been a documented success in estimating ETa in regions around the world, especially the semi-arid regions of the western United States, it has not been applied in the Mid-Atlantic region of the United States or examined under different irrigation regimes like subsurface drip (SDI) and central pivot irrigation (CPI). This study compares cumulative ETa from corn and soybean crops under CPI and SDI crop fields and provides cumulative ETa images of the fields in southern Delaware. METRIC modeled land surface energy balance data and daily ETa (ETMETRIC) were compared to in-situ observations of incoming solar radiation (RS6́3), surface temperature (Ts), net radiation (R℗Ơn), soil heat flux (G), sensible heat flux (H), latent heat flux (LE), Eddy Covariance ETa (ETEC), and atmometer ETa (ETatm). Turbulent fluxes (H and LE) were adjusted to force energy balance closure using the Bowen ratio method. In-situ data measurements were fixed to a Delaware Environmental Observing System (DEOS) station bordering the SDI field in Warrington Farm, a University of Delaware owned irrigation research farm. METRIC analysis and validation were performed over various dates within the 2015, 2016, and 2017 growing seasons. Modeled values of RS6́3, T℗Ơs, G, and LE agreed reasonably well with observations, while Rn and H yielded large biases. Biases in H are in part due to the internal design of METRIC of internal calibration, which absorb all other energy balance biases to yield accurate values of ETa. Daily time series of ETMETRIC from the 2016 study period agreed well with ETEC, indicated by moderate correlation (R2 = 0.63) and low RMSE (0.75 mm day-1). Results from the 2017 study period were unfavorable (R2 = 0.33, RMSE of 1.13 mm day-1). Less than optimal Landsat coverage over the study area contributed to deviations from observations. Cumulative ETMETRIC was 1.5% and 2.9% greater than ETEC for the 2016 and 2017 study periods, respectively. METRIC analysis was able to detect differences in cumulative ETa℗Ơ of corn and soybean under the CPI system and SDI system. Results indicate that METRIC is a useful tool to create spatial estimates of ETa in an agriculturally intensive area of the mid-Atlantic region.
This book presents research on precipitation partitioning processes in vegetated ecosystems, putting them into a global context. It describes the processes by which meteoric water comes into contact with the vegetation's canopy, typically the first surface contact of precipitation on land. It also discusses how precipitation partitioning by vegetation impacts the amount, patterning, and chemistry of water reaching the surface, as well as the amount and timing of evaporative return to the atmosphere. Although this process has been extensively studied, this is the first review of the global literature on the partitioning of precipitation by forests, shrubs, crops, grasslands and other less-studies plant types. The authors offer global contextualization combined with a detailed discussion of the impacts for the climate and terrestrial ecohydrological systems. As such, this comprehensive overview is a valuable reference tool for a wide range of specialists and students in the fields of geoscience and the environment.
Evapotranspiration is the largest outgoing water flux from the Earth's surface; its accurate quantification is critical for the crop development in conditions of the climate changes from recent decades, and it can contribute to a greater understanding of a range of agricultural ecosystem processes. To evaluate the hydric requirements of the crops, it was agreed that they should be reported to a maximum global evapotranspiration called potential evapotranspiration. To estimate this variable, a variety of methods were developed, each with its benefits as well as trade-offs. Their use, however, is laborious due to their complexity and of the large number of parameters required. In this book, specialists' concerns worldwide to develop simple but reliable methodologies - with less data requirement - which will give accurate and appropriate results - are presented. In addition, a study of the physics of the moisture evaporation process from porous media to elucidate what are the mechanisms of moisture migration from granular biopesticides is presented in the last chapter.
