Representativeness of Eddy-Covariance flux footprints for areas surrounding AmeriFlux sites

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JD028447

Evaluating Different Machine Learning Methods for Upscaling Evapotranspiration from Flux Towers to the Regional Scale

We used moisture Bowen ratio flux tower data and the enhanced vegetation index (EVI) from the moderate resolution imaging spectrometer (MODIS) on the Terra satellite to measure and scale evapotranspiration (ET) over sparsely vegetated grassland and shrubland sites in a semiarid watershed in southeastern Arizona from 2000 to 2004. The grassland tower site had higher mean annual ET (336 mm yr−1) than the shrubland tower site (266 mm yr−1) (P r 2 = 0.74 ) by a single multiple regression equation. The regression equation relating ET to EVI and P was used to scale ET over 25 km2 areas of grassland and shrubland around each tower site. Over the study, ratios of T to ET ranged from 0.75 to 1.0. Winter rains stimulated spring ET, and a large rain event in fall, 2000, stimulated ET above T through the following year, indicating that winter rain stored in the soil profile can be an important component of the plants’ water budget during the warm season in this ecosystem. We conclude that remotely sensed vegetation indices can be used to scale ground measurements of ET over larger landscape units in semiarid ranglelands, and that the vegetation communities in this landscape effectively harvest the available precipitation over a period of years, even though precipitation patterns are variably seasonally and interannually.

Relationship Between Evapotranspiration and Precipitation Pulses in a Semiarid Rangeland Estimated by Moisture Flux Towers and MODIS Vegetation Indices

Grasslands in northern China and the Qinghai-Tibetan plateau are particularly important to both ecosystem functioning and pastoral livelihoods. Although there are numerous degradation studies on the effect of livestock grazing across the region, they are largely only published in Chinese, and most focus on single sites. Based on case studies from 100 sites, covering a mean annual precipitation gradient of 95–744 mm, we present a comprehensive, internationally accessible review on the impact of livestock grazing on vegetation and soils. We compared ungrazed or slightly grazed sites with moderately and heavily grazed sites by evaluating changes in two indicator groups: vegetation (plant species richness, vegetation cover, aboveground biomass, belowground biomass and root/shoot ratio) and soil (pH, bulk density, organic C, total N, total P and available P). Most indicators declined with intensified grazing, while soil pH, bulk density and belowground biomass increased. Available P showed no clear response. Variables within indicator groups were mostly linearly correlated at a given grazing intensity. Relative grazing effects on different indicators varied along specific abiotic gradients. Grazing responses of plant species richness, aboveground biomass, soil bulk density, total N and available P interacted with precipitation patterns, while grazing effects on belowground biomass were influenced by temperature. Elevation had impact on grazing responses of aboveground biomass and soil organic carbon. Complex grazing effects reflect both methodological inconsistency and ecological complexity. Further assessments should consider specific characteristics of different indicators in the context of the local environment.

Vegetation and soil responses to livestock grazing in Central Asian grasslands: a review of Chinese literature

Locusts are grasshoppers (Orthoptera: Acrididae) that are characterised by their capacity for extreme population density-dependent polyphenism, transforming between a cryptic solitarious phase that avoids other locusts, and a swarming gregarious phase that aggregates and undergoes collective migration. The two phases differ in many aspects of behaviour, physiology and ecology, making locusts a useful model through which to investigate the phenotypic interface of molecular processes and environmental cues. This review summarises recent progress in understanding the mechanisms and consequences of locust phase change, from differential gene expression and epigenetic regulation through to neuronal plasticity and altered behaviour. The impact of techniques such as RNA interference and the sequencing of the first locust genome are discussed, and we consider the evidence from comparative analyses between related locust species for the possible evolution of locust-like phenotypic plasticity. Collective movement, and new ways of measuring the behaviour of both migrating bands in the field and individuals in the laboratory, are analysed. We also examine the environmental factors that affect phase change, along with the wider impact of land use and management strategies that may unwittingly create environments conducive to outbreaks. Finally, we consider the human costs of locust swarming behaviour, and use combined social, economic and environmental approaches to suggest potential ways forward for locust monitoring and management.

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From Molecules to Management: Mechanisms and Consequences of Locust Phase Polyphenism

Increasing grazing pressure and climate change affect nitrogen (N) dynamics of grassland ecosystems in the Eurasian steppe belt with unclear consequences for future delivery of essential services such as forage production, C sequestration, and diversity conservation. The identification of key processes responsive to grazing is crucial to optimize grassland management. In this comprehensive case study of a Chinese typical steppe, we present an in-depth analysis of grazing effects on N dynamics, including the balance of N gains and losses, and N cycling. N pools and fluxes were simultaneously quantified on three grassland sites of different long-term grazing intensities. Dust deposition, wind erosion, and wet deposition were the predominant but most variable processes contributing to N losses and gains. Heavy grazing increased the risk of N losses by wind erosion. Hay-making and sheep excrement export to folds during nighttime keeping were important pathways of N losses from grassland sites. Compared to the...

N balance and cycling of Inner Mongolia typical steppe: a comprehensive case study of grazing effects

The goal of this study is to characterize the sensible ( H ) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50–100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decomposition of the turbulence data enables a spatial discretization of 90 m of the flux measurements. For a total of 8446 flux observations during 12 flights, MODIS land surface temperature (LST) and enhanced vegetation index (EVI) in each flux footprint are determined. Boosted regression trees are then used to infer an environmental response function (ERF) between all flux observations ( H , LE) and biophysical (LST, EVI) and meteorological drivers. Numerical tests show that ERF predictions covering the entire Xilin River catchment (a3670 km 2 ) are accurate to ≤18% (1 σ). The predictions are then summarized for each land cover type, providing individual estimates of source strength (36 W m −2 H −2 , 46 W m −2 −2 ) and spatial variability (11 W m −2 H −2 , 14 W m −2 LE −2 ) to a precision of ≤5%. Lastly, ERF predictions of land cover specific Bowen ratios are compared between subsequent flights at different locations in the Xilin River catchment. Agreement of the land cover specific Bowen ratios to within 12 p 9% emphasizes the robustness of the presented approach. This study indicates the potential of ERFs for (i) extending airborne flux measurements to the catchment scale, (ii) assessing the spatial representativeness of long-term tower flux measurements, and (iii) designing, constraining and evaluating flux algorithms for remote sensing and numerical modelling applications.

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Spatially explicit regionalization of airborne flux measurements using environmental response functions

/pdf/spatial-resolution-and-regionalization-of-airborne-flux-41ysiu0fth.pdf

Spatial resolution and regionalization of airborne flux measurements using environmental response functions

The purpose of this work is to research the spill and diffusion characteristics of liquid hydrogen in confined cabin with air supplying and vent. The spill and diffusion behavior of liquid hydrogen in the confined cabin with air supplying and vent was simulated using Fluent software. The feasibility of the model was verified by the experimental results. The research results show that the numerical simulation model can simulate to predict the diffusion process of liquid hydrogen well and has application value for engineering. The diffusion cloud after the spill of liquid hydrogen is gathering at the top and slowly spread to the surrounding which is different from the open environment. The process of liquid hydrogen spill can be divided into three stages, among which the concentration of cloud clusters changes sharply in the spilling stage. Low wind speed can affect the inclination angle of the diffuse cloud, and it is concluded that wind speed is also the main factor affecting the movement of the diffusion cloud. The research results are expected to provide a reference for standard formulation and design of liquid hydrogen applications.

X. H. Zheng

Papers

N balance and cycling of Inner Mongolia typical steppe: a comprehensive case study of grazing effects

Spatially explicit regionalization of airborne flux measurements using environmental response functions

Spatial resolution and regionalization of airborne flux measurements using environmental response functions

Numerical Simulation of Liquid Hydrogen Spilling in the Confined Cabin with Air Supplying and Vent