While large‐scale terrestrial evapotranspiration (ET) information is essential for our understanding of the Earth's water and energy cycles, substantial differences exist in current global ET ...products due partly to uncertainties in soil‐ and vegetation‐related parameters and/or precipitation forcing. Here a calibration‐free complementary relationship (CR) model, driven purely by routine meteorological forcing (air and dew‐point temperature, wind speed, and net radiation), mainly from ERA5, was employed to estimate global ET rates during 1982–2016. Modeled ET agrees favorably with (a) monthly eddy‐covariance measurements of 129 global FLUXNET sites, and; (b) water‐balance‐derived ET of 52 basins at the multiyear mean and annual scales. Additional evaluations demonstrate that the CR is very competitive, in comparison with other 12 widely used global ET products. The 35‐years mean global land ET rate from the CR is 500 ± 6 mm yr−1 (72.3 ± 0.9 × 103 km3 yr−1) with more than 70% of the land area exhibiting increasing annual ET rates over the study period. Globally, CR ET significantly increased at a rate of 0.31 mm yr−1 during 1982–2016, suggesting a 2.2% increase in global land ET over last 35 years. Model inter‐comparisons indicate that global annual CR ET values and their trend are close to the median of not only the 12 ET products chosen but also that of 20 CMIP6 models. Since this calibration‐free CR model requires no precipitation (except in sea‐shore deserts for a subsequent ET correction), vegetation or soil data, it could be incorporated into complex hydrological and/or climate models, thereby facilitating large‐scale hydrological and climate simulations.
Key Points
A global, 30‐years‐plus complementary relationship evapotranspiration (ET) product is developed and validated at the plot and basin scales
This new ET product, derived from a minimal number of inputs without vegetation or soil data, may improve upon previous global ET estimates
Global terrestrial ET rates increased significantly during 1982–2016, particularly in the Northern Hemisphere
Monthly evapotranspiration (ET) rates for 1979–2015 were estimated by the latest, calibration‐free version of the complementary relationship (CR) of evaporation over the conterminous United States. ...The results were compared to similar estimates of three land surface models (Noah, VIC, Mosaic), two reanalysis products (National Centers of Environmental Protection Reanalysis II, ERA‐Interim), two remote‐sensing‐based (Global Land Evaporation Amsterdam Model, Penman‐Monteith‐Leuning) algorithms, and the spatially upscaled eddy‐covariance ET measurements of FLUXNET‐MTE. Model validations were performed via simplified water‐balance derived ET rates employing Parameter‐Elevation Regressions on Independent Slopes Model precipitation, United States Geological Survey two‐ and six‐digit Hydrologic Unit Code (HUC2 and HUC6) discharge, and terrestrial water storage anomalies from Gravity Recovery and Climate Experiment, the latter for 2003–2015. The CR outperforms all other multiyear mean annual HUC2‐averaged ET estimates with root‐mean‐square error = 51 mm/year, R = 0.98, relative bias of −1%, and Nash‐Sutcliffe efficiency = 0.94, respectively. Inclusion of the Gravity Recovery and Climate Experiment data into the annual water balances for the shorter 2003–2015 period does not have much effect on model performance. Similarly, the CR outperforms all other models for the linear trend of the annual ET rates over the HUC2 basins. Over the significantly smaller HUC6 basins where the water‐balance validation is more uncertain, the CR still outperforms all other models except FLUXNET‐MTE, which has the advantage of possible local ET measurements, a benefit that clearly diminishes at the HUC2 scale. As the employed CR is calibration‐free and requires only very few meteorological inputs, yet it yields superior ET performance at the regional scale, it may serve as a diagnostic and benchmarking tool for more complex and data intensive models of terrestrial evapotranspiration rates.
Key Points
Nine gridded ET products were evaluated against water‐balance estimates of the mean—and linear trend in—annual ET rates over HUC2 and HUC6 basins of the conterminous United States
The calibration‐free CR with only minimal meteorological data requirement performed the best overall
Due to its performance, data efficiency, and simple structure the calibration‐free CR could serve as a benchmarking and diagnostic tool for more complex models
•Long-term mean TP-averaged annual ET is 353±24 mm, with 64% from soil evaporation.•Annual ET from TP increased significantly during 1982–2016.•Precipitation enhancement is the dominant driver of ...increase in TP-averaged ET.•The dominant drivers of ET trend are spatially heterogeneous over TP.•Vegetation change plays a less important role than climatic factors in ET trend.
While terrestrial evapotranspiration (ET) from the Tibetan Plateau (TP) plays a key role in modulating water storage change in the Asian Water Tower, the magnitude, trend, and drivers of ET remain poorly understood in this region due partially to sparse ground measurements. This study used a water-carbon coupled biophysical model, Penman-Monteith-Leuning Version 2 (PML_V2), to characterize the variations in ET across TP during 1982–2016 and its drivers. Model parameters of PML_V2 were calibrated against ground-observed data from 14 eddy-covariance flux towers. Plot- and basin-scale validations demonstrate that the PML_V2 is robust enough in simulating both magnitude and trend in ET. The 35-year mean annual ET rates decrease from the southeastern to the northwestern TP, leading to a TP-averaged value of 353 ± 24 mm yr−1. Soil evaporation is the main component (64%) of ET, followed by plant transpiration (31%) and canopy evaporation (5%). From 1982 to 2016, TP-averaged ET increased significantly with a rate of 1.87 ± 0.25 mm yr−2 (p < 0.001) due primarily to precipitation enhancement. Spatially, precipitation is the dominant driver that controls ET trend over most parts of TP except certain regions in the southeastern and eastern TP, where net radiation and temperature do so instead, respectively. This is because 68% of the TP area is dryland with the aridity index < 0.65. While LAI appears less important than climate factors over much of TP, its relative contribution to ET trend exceeds 20% in many parts of eastern TP, indicating that vegetation change played a nonnegligible role in regulating annual ET variations over certain regions where LAI varied substantially. Our results are of vital importance for facilitating the understanding of hydrological processes over the Asian Water Tower.
Dietary amino acids (AAs) are not only absorbed and metabolized by enterocytes but also available to the microbiota in the gut in mammals. In addition to serving as the materials for protein ...synthesis, AAs can act as precursors for numerous metabolic end products in reactions involving the intestinal mucosa and microbiota. After penetrating the epithelial barrier, microbial metabolites can enter and accumulate in the host circulatory system, where they are sensed by immune cells and then elicit a wide range of biological functions via different receptors and mechanisms. Some intestinal bacteria can also synthesize certain AAs, implying that the exchange of AAs between hosts and microorganisms is bidirectional. Changes in AA composition and abundance can affect AA‐metabolizing bacterial communities and modulate macrophages and dendritic cells via toll‐like receptors (TLRs), autoinducer‐2 (AI‐2), and NOD‐like receptors (NLRs), and also regulate the gut‐microbiome‐immune axis via aryl hydrocarbon receptor (AhR), serotonin/5‐hydroxytryptamine (5‐HT), and other signaling pathways, all of which play critical roles in regulating the intestinal mucosal immunity and microbiota directly or indirectly, contributing to intestinal homeostasis. Therefore, the current findings of the effects of certain functional AAs on the gut‐microbiome‐immune axis are reviewed, illustrating signaling pathways of tryptophan (Trp), glutamine (Gln), methionine (Met), and branched‐chain AAs (BCAAs) in the intestinal barrier and regarding immunity via crosstalk with their receptors or ligands. These findings have shed light on the clinical applications of dietary AAs in improving gut microbiota and mucosal immunity, therefore benefiting the gut as well as local and systemic health.
The emergence of multimedia data has enriched people’s lives and work and has penetrated into education, finance, medical, military, communications, and other industries. The text data takes up a ...small space, and the network transmission speed is fast. However, due to its richness, the multimedia data makes it occupy an ample space. Some high-definition multimedia information even reaches the GB level, and the multimedia data network transmission is relatively slow. Compared with the traditional scalar data, the multimedia data better describes the characteristics of the transaction, but at the same time, the multimedia data itself has a large capacity and must be compressed. Nodes of wireless multimedia sensor networks have limited ability to process data. Traditional data compression schemes require high processing power of nodes and are not suitable for sensor networks. Therefore, distributed video codec scheme in recent years becomes one of the hot multimedia sensor network technologies, which is a simple coding scheme, coding complexity of decoding performance. In this paper, distributed video codec and its associated knowledge based on the study present a distributed video coding scheme and its improvements. Aiming at the problem that the traditional distributed video coding scheme cannot accurately decode the motion severe region and the boundary region, a distributed video coding algorithm based on gradient-domain ROI is proposed, which can enhance the coding efficiency of the severe motion region and improve the decoded image while reducing the code rate and quality, ultimately reducing sensor node energy consumption.
Alpine grassland in the Tibetan Plateau
This study used Noah-MP to simulate the energy fluxes net radiation (Rn), latent (λE) and sensible (H) heat fluxes in two typical alpine ecosystems in the ...Tibetan Plateau. The effectivenesses of new parameterization schemes for the roughness length for heat transfer and the root distribution were evaluated. By further using multi-scenario modeling, the responses of land evapotranspiration (ET), soil evaporation (Es) and vegetation transpiration (Tr) to changes in precipitation, solar radiation and air temperature were investigated.
The default Noah-MP largely overestimates (underestimates) Rn and λE, but tends to underestimate (overestimate) H in alpine meadow (alpine steppe). After incorporating two newly-developed parameterization schemes, the accurancy of Noah-MP has been improved in alpine meadow for Rn and λE, while in alpine steppe only H has been improved. The ET, Es and Tr in alpine meadow are more sensitive to decreasing precipitation than that to increasing precipitation. In alpine steppe, ET and Es increase with increasing precipitation, while Tr responds weakly to changes in precipitation; The effect of temperature change on ET appears weak in both ecosystems. However, Tr shows negative responses to increased temperature and such responses in alpine steppe are more remarkable than those in alpine meadow, suggesting the former may be more vulnerable to future warming than the latter.
•New zoh and root distribution parameterization schemes developed for Noah-MP.•Noah-MP has been largely improved in alpine meadow, especially for Rn and λE.•Error in H in alpine steppe is mitigated, but little change is seen for Rn and λE.•Quantifying responses of ET to varying meteorological conditions in two ecosystems.
•The end date of snow cover has significantly advanced in most parts of Eurasia.•Decline of snow cover persistence period in Central Asia and western Tibetan Plateau.•Snow-free breaks mainly occurred ...in the Tibetan Plateau and Central Asia.
Changes in the extent and amount of snow cover in Eurasia are of great interest because of their vital impacts on the global climate system and regional water resource management. This study investigated the spatial and temporal variability of the snow cover extent (SCE) and snow water equivalent (SWE) of the continental Eurasia using the Northern Hemisphere Equal-Area Scalable Earth Grid (EASE-Grid) Weekly SCE data for 1972–2006 and the Global Monthly EASE-Grid SWE data for 1979–2004. The results indicated that, in general, the spatial extent of snow cover significantly decreased during spring and summer, but varied little during autumn and winter over Eurasia in the study period. The date at which snow cover began to disappear in spring has significantly advanced, whereas the timing of snow cover onset in autumn did not vary significantly during 1972–2006. The snow cover persistence period declined significantly in the western Tibetan Plateau as well as partial area of Central Asia and northwestern Russia, but varied little in other parts of Eurasia. “Snow-free breaks” (SFBs) with intermittent snow cover in the cold season were principally observed in the Tibetan Plateau and Central Asia, causing a low sensitivity of snow cover persistence period to the timings of snow cover onset and disappearance over the areas with shallow snow. The averaged SFBs were 1–14 weeks during the study period and the maximum intermittence could even reach 25 weeks in certain years. At a seasonal scale, SWE usually peaked in February or March, but fell gradually since April across Eurasia. Both annual mean and annual maximum SWE decreased significantly during 1979–2004 in most parts of Eurasia except for eastern Siberia as well as northwestern and northeastern China. The possible cross-platform inconsistencies between two passive microwave radiometers may cause uncertainties in the detected trends of SWE here, suggesting an urgent need of producing a long-term, more homogeneous SWE product in future.
There is growing recognition that composition and metabolic activity of the gut microbiota can be modulated by the dietary proteins which in turn impact health. The amino acid composition and ...digestibility of proteins, which are influenced by its source and amount of intake, play a pivotal role in determining the microbiota. Reciprocally, it appears that the gut microbiota is also able to affect protein metabolism which gives rise to the view that function between the microbiota and protein can proceed in both directions. In response to the alterations in dietary protein components, there are significant changes in the microbial metabolites including short chain fatty acids (SCFAs), ammonia, amines, gases such as hydrogen, sulfide and methane which are cytotoxins, genotoxins and carcinogens associated with development of colon cancer and inflammatory bowel diseases. A suitable ratio between protein and carbohydrate or even a low protein diet is recommended based on the evidence that excessive protein intake adversely affects health. Supplying high and undigested proteins will encourage pathogens and protein-fermenting bacteria to increase the risk of diseases. These changes of microbiota can affect the gut barrier and the immune system by regulating gene expression in relevant signaling pathways and by regulating the secretion of metabolites. The objective of this review is to assess the impact of dietary proteins on microbiota composition and activity in the gastrointestinal tract. Attention should be given to the dietary strategies with judicious selection of source and supplementation of dietary protein to benefit gut health.
Ectopic expression of a single neural transcription factor NeuroD1 can reprogram reactive glial cells into functional neurons both in vitro and in vivo, but the underlying mechanisms are not well ...understood yet. Here, we used RNA‐sequencing technology to capture the transcriptomic changes at different time points during the reprogramming process. We found that following NeuroD1 overexpression, astroglial genes (ACTG1, ALDH1A3, EMP1, CLDN6, SOX21) were significantly downregulated, whereas neuronal genes (DCX, RBFOX3/NeuN, CUX2, RELN, SNAP25) were significantly upregulated. NeuroD family members (NeuroD1/2/6) and signaling pathways (Wnt, MAPK, cAMP) as well as neurotransmitter receptors (acetylcholine, somatostatin, dopamine) were also significantly upregulated. Gene co‐expression analysis identified many central genes among the NeuroD1‐interacting network, including CABP7, KIAA1456, SSTR2, GADD45G, LRRTM2, and INSM1. Compared to chemical conversion, we found that NeuroD1 acted as a strong driving force and triggered fast transcriptomic changes during astrocyte‐to‐neuron conversion process. Together, this study reveals many important downstream targets of NeuroD1 such as HES6, BHLHE22, INSM1, CHRNA1/3, CABP7, and SSTR2, which may play critical roles during the transcriptomic landscape shift from a glial profile to a neuronal profile.
•ETwb of 56 large river basins (1983–2016) are derived from multi-source datasets.•Gauge undercatch in precipitation is corrected to mitigate underestimation of ETwb.•The 12 ETwb time-series are ...merged using Bayesian-based three-cornered hat method.•The uncertainty in ETwb is due primarily to the uncertainty in precipitation.
A thorough validation of global terrestrial evapotranspiration (ET) models requires reliable ground-observed ET data. While the open-access eddy-covariance flux measurements are widely used for such a purpose, they have certain drawbacks, and thus, other alternative publicly available reference datasets are urgently needed. Using remote sensing and ground-based observational data, this study provides water-balance-based evapotranspiration (ETwb) estimates for 56 large (>105 km2) river basins of the world over the 1983–2016 period. For each basin, the observed runoff and four different precipitation (Prec) data sources were combined with three types of terrestrial water storage change (dS) estimates, yielding altogether 12 annual ETwb time-series. An optimally merged ETwb time-series was eventually produced using the Bayesian-based three-cornered hat method. The relative uncertainty in the ETwb estimates is less than 10 % in most basins and it stems primarily from the uncertainty in Prec. In summary, this new ETwb dataset has the following advantages: i) The gauge undercatch in Prec was corrected, thus mitigating the well-known general underestimation of ETwb in mid- and high-latitudes; ii) Multiple Prec and dS datasets were combined to account for the uncertainty in the water balance approach, thereby enabling the quantification of the uncertainty in ETwb and its sources, and; iii) The ETwb dataset stretches more than three decades, making it appropriate for evaluating long-term trends in global ET models. This ETwb dataset is publicly available (https://data.tpdc.ac.cn/en/data/e010cd0d-0881-4e7e-9d63-d36992750b04) and may serve as a benchmarking tool to calibrate/validate large-scale ET models for an improved understanding of regional- and/or global-scale ET processes.
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