scholarly journals Energy Exchange and Evapotranspiration over the Ejina Oasis Riparian Forest Ecosystem with Different Land-Cover Types

Water ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 3424
Author(s):  
Weizhen Wang ◽  
Feinan Xu ◽  
Jiemin Wang
Keyword(s):  
Water Vapor ◽  
Energy Balance ◽  
Forest Ecosystem ◽  
Riparian Forest ◽  
Growing Season ◽  
Energy Balance Closure ◽  
Tamarix Chinensis ◽  
Barren Land ◽  
Ejina Oasis ◽  
Flux Data

Investigating the energy and water vapor exchange in oasis riparian forest ecosystems is of significant importance to improve scientific understanding of land surface processes in extreme arid regions. The Heihe Watershed Allied Telemetry Experimental Research (HiWATER) provided many observations of water vapor and heat fluxes from riparian forest ecosystem by using a network of eddy-covariance (EC) systems installed over representative surfaces in the Ejina Oasis, which is located in the downstream areas of the Heihe River Basin, northwestern China. Based on EC flux measurements and meteorological data performed at five stations and covering representative surface types of Populus euphratica tree with associated Tamarix chinensis shrub, Tamarix chinensis shrubland, cantaloupe cropland, and barren-land, this study explored the spatio-temporal patterns of heat and water vapor fluxes over the Ejina Oasis riparian forest ecosystem with five different surface types over the course of a growing season in 2014. Energy balance closure of the flux data was evaluated; footprint analysis for each EC site was also performed. Results showed that energy balance closure for the flux data was reasonably good, with average energy balance ratio (EBR) of 1.03. The seasonal variations in net radiation (Rn), latent (LE), and sensible heat flux (H) over the five contrasting surfaces were similar, and a reverse seasonal change was observed in energy partitioning into LE and H. Remarkable differences in Rn, LE, and H between the five surfaces were explored preliminarily, associated closely with the soil properties and foliage phenology. Over the growing season (May–October) in 2014, the total ET ranged 622–731 mm for mixed forest of P. euphratica trees with associated T. chinensis shrubs with average daily ET of 3.6–4.2 mm; ET from T. chinensis shrubland was about 541 mm, with average daily ET of 3.6 mm. ET for barren-land was 195 mm. The total ET in irrigated cantaloupe cropland with plastic mulch was 431 mm for its four-month growing period with a total average of 3.8 mm d−1. Determination of ET over riparian forest ecosystem helps to improve reasonable use of limited water resource in the Ejina Oasis.

scholarly journals Evaluation of Evapotranspiration from Eddy Covariance Using Large Weighing Lysimeters

Agronomy ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 99 ◽  
Author(s):  
Jerry Moorhead ◽  
Gary Marek ◽  
Prasanna Gowda ◽  
Xiaomao Lin ◽  
Paul Colaizzi ◽  
...  
Keyword(s):  
Energy Balance ◽  
Eddy Covariance ◽  
Water Use ◽  
Growing Season ◽  
Irrigation Scheduling ◽  
Error Rates ◽  
Energy Balance Closure ◽  
Crop Water ◽  
Crop Water Use ◽  
Hourly Data

Evapotranspiration (ET) is an important component in the water budget and used extensively in water resources management such as water planning and irrigation scheduling. In semi-arid regions, irrigation is used to supplement limited and erratic growing season rainfall to meet crop water demand. Although lysimetery is considered the most accurate method for crop water use measurements, high-precision weighing lysimeters are expensive to build and operate. Alternatively, other measurement systems such as eddy covariance (EC) are being used to estimate crop water use. However, due to numerous explicit and implicit assumptions in the EC method, an energy balance closure problem is widely acknowledged. In this study, three EC systems were installed in a field containing a large weighing lysimeter at heights of 2.5, 4.5, and 8.5 m. Sensible heat flux (H) and ET from each EC system were evaluated against the lysimeter. Energy balance closure ranged from 64% to 67% for the three sensor heights. Results showed that all three EC systems underestimated H and consequently overestimated ET; however, the underestimation of H was greater in magnitude than the overestimation of ET. Analysis showed accuracy of ET was greater than energy balance closure with error rates of 20%–30% for half-hourly values. Further analysis of error rates throughout the growing season showed that energy balance closure and ET accuracy were greatest early in the season and larger error was found after plants reached their maximum height. Therefore, large errors associated with increased biomass may indicate unaccounted-for energy stored in the plant canopy as one source of error. Summing the half-hourly data to a daily time-step drastically reduced error in ET to 10%–15%, indicating that EC has potential for use in agricultural water management.

scholarly journals Water vapor density and turbulent fluxes from three generations of infrared gas analyzers

2020 ◽  
Author(s):  
Seth Kutikoff ◽  
Xiaomao Lin ◽  
Steven R. Evett ◽  
Prasanna Gowda ◽  
David Brauer ◽  
...  
Keyword(s):  
Water Vapor ◽  
Energy Balance ◽  
Growing Season ◽  
Fast Response ◽  
Static Stability ◽  
Turbulent Fluxes ◽  
Density Fluctuations ◽  
Systematic Bias ◽  
Vapor Density ◽  
Three Generations

Abstract. Fast-response infrared gas analyzers (IRGAs) have been widely used over three decades in many ecosystems for long-term monitoring of water vapor fluxes in the surface layer of the atmosphere. While some of the early IRGA sensors are still used in these national and/or regional eco-flux networks, optically-improved IRGA sensors are newly employed in the same networks. The purpose of this study was to evaluate the performance of water vapor density and flux data from three generations of IRGAs – LI-7500, LI-7500A, and LI-7500RS (LI-COR Bioscience, Inc., Nebraska, USA) – over the course of a growing season in Bushland, Texas, USA in an irrigated maize canopy for 90 days. The energy balance ratio, which is the sum of turbulent fluxes divided by the sum of surface available energy, was used to assess systematic biases of the IRGA sensors for evapotranspiration (ET). Water vapor density measurements were in generally good agreement, but temporal drift occurred in different directions and magnitudes. Means exhibited mostly shift changes that did not impact the flux magnitudes, while variances of water vapor density fluctuations were occasionally in poor agreement, especially following rainfall events. LI-7500 variances were largest compared to recent LI-7500RS and LI-7500A results manifesting in widened cospectra, especially under unstable and neutral static stability. Agreement among the sensors was best under the typical irrigation-cooled boundary layer, with a 14 % interinstrument coefficient of variability under advective conditions. Generally, the smallest variances occurred with the LI-7500RS, and high-frequency spectral corrections were larger for these measurements resulting in similar fluxes between the LI-7500A and LI-7500RS. Fluxes from the LI-7500 were best representative of growing season ET based on a world-class lysimeter reference measurement but using the energy balance ratio as an estimate of systematic bias corrected most of the differences among measured fluxes.

Ground-based lidar observations of vertical aersosol and water vapor profiles within the boundary layer over heterogeneous terrain

2021 ◽  
Author(s):  
Johannes Speidel ◽  
Hannes Vogelmann ◽  
Matthias Perfahl ◽  
Matthias Mauder ◽  
Luise Wanner
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Energy Balance ◽  
Transport Processes ◽  
Precipitation Forecast ◽  
Closure Problem ◽  
Energy Balance Closure ◽  
Heterogeneous Terrain ◽  
Ground Based Lidar ◽  
Aerosol Backscatter

<p>Connecting the earth's surface with the free troposphere, the planetary boundary layer (PBL) comprises complex dynamics of turbulent behavior. This especially applies for areas with heterogeneous terrain. Relevant near-ground processes such as released energy fluxes and the emission of aerosols and trace gases directly interact with the atmosphere. Therefore, the PBL's physical state is determined both by the near-ground processes as well as entrainment of air parcels from higher layers. The mainly turbulence-driven transport of particles and properties throughout the PBL constrain a comprehensive understanding of the PBL's behavior. Hence, the energy balance closure problem as well as errors in precipitation forecast in long-term numerical weather predictions, amongst others, remain unresolved challenges. Here, ground-based lidar profiling is a well suitable method for observing the PBL, as data sampling allows for high temporal and vertical resolutions (Here: Sampling rate of 100\,Hz and 7.5\,m). During the CHEESEHEAD campaign, carried out in summer 2019, our newly developed ATMONSYS lidar performed measurements over complex terrain in northern Wisconsin. There, our lidar system was embedded in a dense network of multiple in-situ and remote sensing instruments. The central aim of this campaign was to further contribute to solve the energy balance closure problem. With the ATMONSYS lidar, vertical columns of aerosol backscatter coefficients, water vapor and temperature have been recorded. The presented work shows what the data is suitable for in terms of resolution and temporal extent in the first place. As a second point, focus is given on structure and variability of aerosol backscatter coefficient distributions and water vapor concentrations as well as their implications on the prevailing state of the PBL. Based on the presented findings, we discuss the potential and suitability of this experimental data for deriving transport processes within the PBL.</p>

scholarly journals flux-data-qaqc: A Python Package for Energy Balance Closure and Post-Processing of Eddy Flux Data

2021 ◽  
Vol 6 (66) ◽  
pp. 3418
Author(s):  
John Volk ◽  
Justin Huntington ◽  
Richard Allen ◽  
Forrest Melton ◽  
Martha Anderson ◽  
...  
Keyword(s):  
Energy Balance ◽  
Energy Balance Closure ◽  
Eddy Flux ◽  
Post Processing ◽  
Flux Data ◽  
Python Package

scholarly journals Energy balance closure at FLUXNET sites

2002 ◽  
Vol 113 (1-4) ◽  
pp. 223-243 ◽  
Author(s):  
Kell Wilson ◽  
Allen Goldstein ◽  
Eva Falge ◽  
Marc Aubinet ◽  
Dennis Baldocchi ◽  
...  
Keyword(s):  
Energy Balance ◽  
Energy Balance Closure

scholarly journals Analysing surface energy balance closure and partitioning over a semi-arid savanna FLUXNET site in Skukuza, Kruger National Park, South Africa

2017 ◽  
Vol 21 (7) ◽  
pp. 3401-3415 ◽  
Author(s):  
Nobuhle P. Majozi ◽  
Chris M. Mannaerts ◽  
Abel Ramoelo ◽  
Renaud Mathieu ◽  
Alecia Nickless ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Surface Energy ◽  
Latent Heat ◽  
Surface Energy Balance ◽  
Sensible Heat Flux ◽  
Dry Season ◽  
Energy Balance Closure ◽  
Net Radiation ◽  
Wet Season

Abstract. Flux towers provide essential terrestrial climate, water, and radiation budget information needed for environmental monitoring and evaluation of climate change impacts on ecosystems and society in general. They are also intended for calibration and validation of satellite-based Earth observation and monitoring efforts, such as assessment of evapotranspiration from land and vegetation surfaces using surface energy balance approaches. In this paper, 15 years of Skukuza eddy covariance data, i.e. from 2000 to 2014, were analysed for surface energy balance closure (EBC) and partitioning. The surface energy balance closure was evaluated using the ordinary least squares regression (OLS) of turbulent energy fluxes (sensible (H) and latent heat (LE)) against available energy (net radiation (Rn) less soil heat (G)), and the energy balance ratio (EBR). Partitioning of the surface energy during the wet and dry seasons was also investigated, as well as how it is affected by atmospheric vapour pressure deficit (VPD), and net radiation. After filtering years with low-quality data (2004–2008), our results show an overall mean EBR of 0.93. Seasonal variations of EBR also showed the wet season with 1.17 and spring (1.02) being closest to unity, with the dry season (0.70) having the highest imbalance. Nocturnal surface energy closure was very low at 0.26, and this was linked to low friction velocity during night-time, with results showing an increase in closure with increase in friction velocity. The energy partition analysis showed that sensible heat flux is the dominant portion of net radiation, especially between March and October, followed by latent heat flux, and lastly the soil heat flux, and during the wet season where latent heat flux dominated sensible heat flux. An increase in net radiation was characterized by an increase in both LE and H, with LE showing a higher rate of increase than H in the wet season, and the reverse happening during the dry season. An increase in VPD is correlated with a decrease in LE and increase in H during the wet season, and an increase in both fluxes during the dry season.

scholarly journals Energy balance measurements over a banana orchard in the Semiarid region in the Northeast of Brazil

2009 ◽  
Vol 44 (11) ◽  
pp. 1365-1373 ◽  
Author(s):  
Carlos Antonio Costa dos Santos ◽  
Bernardo Barbosa da Silva ◽  
Tantravahi Venkata Ramana Rao ◽  
Christopher Michael Usher Neale
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Eddy Covariance ◽  
Heat Fluxes ◽  
Irrigation District ◽  
Semiarid Region ◽  
Energy Balance Closure ◽  
Wet Season ◽  
Growing Seasons ◽  
Eddy Covariance System

The objective of this work was to evaluate the reliability of eddy covariance measurements, analyzing the energy balance components, evapotranspiration and energy balance closure in dry and wet growing seasons, in a banana orchard. The experiment was carried out at a farm located within the irrigation district of Quixeré, in the Lower Jaguaribe basin, in Ceará state, Brazil. An eddy covariance system was used to measure the turbulent flux. An automatic weather station was installed in a grass field to obtain the reference evapotranspiration (ET0) from the combined FAO-Penman-Monteith method. Wind speed and vapor pressure deficit are the most important variables on the evaporative process in both growing seasons. In the dry season, the heat fluxes have a similar order of magnitude, and during the wet season the latent heat flux is the largest. The eddy covariance system had acceptable reliability in measuring heat flux, with actual evapotranspiration results comparing well with those obtained by using the water balance method. The energy balance closure had good results for the study area, with mean values of 0.93 and 0.86 for the dry and wet growing seasons respectively.

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