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Estimating evaporation from standard meteorological data continues to be an active area of research and practical application. Here we report on recent progress in using standard meteorology data to estimate potential, reference a...
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Estimating evaporation from standard meteorological data continues to be an active area of research and practical application. Here we report on recent progress in using standard meteorology data to estimate potential, reference and actual evaporation from terrestrial landscapes as well as evaporation from lakes and reservoirs. We also address recent enhancements to standard methodologies through use of remote sensing and data-driven procedures. From our report we observe that remote sensing offers significant potential for mapping spatial variations in evaporation. There has been limited progress in estimating actual evaporation via the complementary relationship, whereas applications of the Penman-Monteith and related equations incorporating actual surface resistance term(s) have dominated the recent literature.
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Oceanic evaporation via the East Asian Monsoon (EAM) has been regarded as the major source of precipitation over China, but a recent study estimated that terrestrial evaporation might contribute up to 80% of the precipitation in t...
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Oceanic evaporation via the East Asian Monsoon (EAM) has been regarded as the major source of precipitation over China, but a recent study estimated that terrestrial evaporation might contribute up to 80% of the precipitation in the country. To explain the contradiction, this study presents a comprehensive analysis of the contribution of oceanic and terrestrial evaporation to atmospheric moisture and precipitation in China's major river basins. The results show that from 1980 to 2010, the mean annual atmospheric moisture (precipitable water) over China was 13.7 mm, 39% of which originates from oceanic evaporation and 61% from terrestrial evaporation. The mean annual precipitation was 737 mm, 43% of which originates from oceanic evaporation and 57% from terrestrial evaporation. Oceanic evaporation makes a greater contribution to atmospheric moisture and precipitation in the East Asian Monsoon Region in South and East China than terrestrial evaporation does. Particularly, for the Pearl River and southeastern rivers, oceanic evaporation contributes approximately 65% of annual precipitation and more than 70% of summer precipitation. Meanwhile, terrestrial evaporation contributes more precipitation in northwest China due to the westerly wind. For the northwestern rivers, terrestrial evaporation from the Eurasian continents contributes more than 70% of precipitation. There is a linear relation between mean annual precipitation and the contribution of oceanic evaporation to precipitation, with a correlation coefficient of 0.92, among the ten major river basins in China.
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Given the importance of terrestrial evaporation (ET) for the water cycle, a fundamental understanding of the water quantity involved in this process is required. As recent observations reveal a widespread ET intensification across...
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Given the importance of terrestrial evaporation (ET) for the water cycle, a fundamental understanding of the water quantity involved in this process is required. As recent observations reveal a widespread ET intensification across the world, it is important to evaluate regional ET variability. The specific objectives of this study are the following: (1) to assess annual and monthly ET trends across Poland, and (2) to reveal seasons and regions with significant ET changes. This study uses the ET estimates acquired from the Global Land Evaporation Amsterdam Model (GLEAM) dataset allowing for multi-year analysis (1980–2020). The Mann–Kendall test and the Sen’s slope were applied to estimate the significance and magnitude of the trends. The results show that a rising temperature, along with small precipitation increase, led to the accelerated ET of 1.36 mm/y. This was revealed by increased transpiration and interception loss not compensated by a decrease in bare soil evaporation and sublimation. The wide-spread higher water consumption especially occurred during the summer months of June, July, and August. Comparing the two subperiods of 1980–2020, it was found that in 2007–2020, the annual ET increased by 7% compared to the reference period of 1980–2006. These results can serve as an important reference for formulating a water resources management strategy in Poland.
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Terrestrial evaporation is essential to the global hydrological cycle and climate systems. It is a complicated energy and mass transfer process that involves radiation, conduction, diffusion, convection, and surface-atmosphere int...
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Terrestrial evaporation is essential to the global hydrological cycle and climate systems. It is a complicated energy and mass transfer process that involves radiation, conduction, diffusion, convection, and surface-atmosphere interactions. The energetic and diffusive controls on evaporation were combined in the contemporary theory (e.g. the Penman-Monteith equation), in which surface-atmosphere interfacial transfer coefficients were adopted and parameterized semi-empirically or empirically to achieve a solution to evaporation. The solution achieved through this parameterization leaves unsolvable uncertainty. Thus, the theory of evaporation remains diagnostic rather than predictive. Here we show that terrestrial evaporation can be predicted without parameterization. Terrestrial evaporation, as a mechanical and thermodynamic process, follows Hamilton's principle in the macro-state. With surface temperature as a generalized coordinate of the Hamiltonian, and incorporating equilibrium evaporation, we present a nonparametric solution in a simple analytical form. We used observational data collected at 26 eddy covariance sites to test the effectiveness and the generality of the solution. Results showed good agreements between the estimated and the observed values, by an absolute difference of 10.3 +/- 20.2 W m(-2) for latent heat flux (evaporation) and -11.8 +/- 21.0 W m(-2) for sensible heat flux, for all the tested sites. Further examination demonstrated that the proposed approach achieved the performance compatible to the Penman-Monteith approach. We anticipate our analysis to be a starting point for more sophisticated investigation into the complex nature of terrestrial evaporation. Its simplicity should have potential value in applications, in addition to contributing to fundamental theory. Crown Copyright (c) 2012 Published by Elsevier B.V
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Study Region Arid and semi-arid regions of Northwest China (NWC) Study Focus Water scarcity poses a significant challenge to the development of NWC. Although the climate is getting warmer and wetter in NWC, there is a clear intens...
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Study Region Arid and semi-arid regions of Northwest China (NWC) Study Focus Water scarcity poses a significant challenge to the development of NWC. Although the climate is getting warmer and wetter in NWC, there is a clear intensification in the trend of regional hydrological aridification. However, the connection between these factors continues to remain elusive to our comprehension. This study investigated the impacts of vegetation changes on terrestrial water storage (TWS) and explored their underlying causes using the Lund-Potsdam-Jena (LPJ) Dynamic Global Vegetation Model based on long-term hydrometeorological data, TWS anomaly data, and Normalized Difference Vegetation Index (NDVI) data. New Hydrological Insights for the Region This study unveils a significant upsurge in NDVI and actual evaporation (E) within NWC during 1982–2019, with distinct prominence observed in cultivated regions. This heightened E emerges as a central driver behind the reduction in surface soil water, root zone soil water, and the continuous decline of TWS across the NWC. The research discerns the amplified E, influenced by both climatic and human activities, as a key contributor to the diminution of TWS within the region. Notably, the contribution of cultivated land E exhibits consistent expansion, while grassland E remains pivotal in TWS reduction. Transpiration (Et) and bare-soil evaporation (Eb) surface as the predominant elements of terrestrial E. The degradation of grasslands leads to intensified Eb, thereby further augmenting E.
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We evaluate a new approach to estimate regional evapotranspiration (ET) across a montane, Mediterranean climate gradient in the San Jacinto and Santa Rosa Mountains of Southern California. Spatially distributed evaporative fractio...
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We evaluate a new approach to estimate regional evapotranspiration (ET) across a montane, Mediterranean climate gradient in the San Jacinto and Santa Rosa Mountains of Southern California. Spatially distributed evaporative fraction (EF) measurements were made monthly from October 2008 to September 2009 at 54 locations across an elevational gradient using a mobile measurement platform, called the Regional Evaporative Fraction Energy Balance (REFEB) method. We used these measurements and the Enhanced Vegetation Index (EVI) from MODerate resolution Imaging Spectroradiometer (MODIS) observations to derive EF at a regional scale. We converted EF to monthly ET using remote-sensing based observations of available energy. We compared the REFEB ET estimates, along with modified Priestly-Taylor (PT) ET estimates driven by MODIS data against four eddy covariance (EC) towers and eight gauged catchments. Both of the satellite-based ET estimates were highly correlated with tower ET observations (r2=0.66 for REFEB and 0.95 for PT). The PT MODIS approach overestimated ET compared to precipitation estimates and stream gauge measurements, while REFEB ET was moderately lower than PT ET. The annual regional REFEB ET (193 mm) was 87 mm less than precipitation (280 mm). REFEB ET underestimated EC tower ET (regression slope=0.78, p<0.001). Regional PT ET (288 mm) exceeded precipitation by 8 mm and significantly overestimated EC tower ET (regression slope=1.43, p<0.001). The relationship between precipitation and ET is not linear, with a break around 290 mm/year, at which point ET becomes nearly constant at 200-300 mm/year with increasing precipitation. This causes a break in the precipitation-runoff relationship, with a disproportionate increase in runoff when precipitation exceeds 290 mm/year. REFEB provides a viable method to estimate regional ET, which is applicable to areas that are poorly constrained by other remote sensing approaches.Digital Object Identifier http://dx.doi.org/10.1016/j.agrformet.2012.07.004
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Iron isotopic compositions measured in chondrules from various chondrites vary between delta Fe-57/Fe-54 = +0.9% and -2.0%, a larger range than for igneous rocks. Whether these compositions were inherited from chondrule precursors...
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Iron isotopic compositions measured in chondrules from various chondrites vary between delta Fe-57/Fe-54 = +0.9% and -2.0%, a larger range than for igneous rocks. Whether these compositions were inherited from chondrule precursors, resulted from the chondrule-forming process itself or were produced by later parent body alteration is as yet unclear. Since iron metal is a common phase in some chondrules, it is important to explore a possible link between the metal formation process and the observed iron isotope mass fractionation. In this experimental study we have heated a fayalite-rich composition under reducing conditions for heating times ranging from 2 min to 6 h. We performed chemical and iron isotope analyses of the product phases, iron metal and silicate glass. We demonstrated a lack of evaporation of Fe from the silicate melt in similar isothermal experiments performed under non-reducing conditions. Therefore, the measured isotopic mass fractionation in the glass, ranging between -0.32% and +3.0%, is attributed to the reduction process. It is explained by the faster transport of lighter iron isotopes to the surface where reduction occurs, and is analogous to kinetic isotope fractionation observed in diffusion couples [Richter, F.M., Davis, A.M., Depaolo, D.J., Watson, E.B., 2003. Isotope fractionation by chemical diffusion between molten basalt and rhyolite. Geochim. Cosmochim. Acta 67, 3905-3923]. The metal phase contains 90 99.8% of the Fe in the system and lacks significant isotopic mass fractionation, with values remaining similar to that of the starting material throughout. The maximum iron isotope mass fractionation in the glass was achieved within 1 h and was followed by an isotopic exchange and re-equilibration with the metal phase (incomplete at similar to 6 h). This study demonstrates that reduction of silicates at high temperatures can trigger iron isotopic fractionation comparable in its bulk range to that observed in chondrules. Furthermore, if metal in Type I chondrules was formed by reduction of Fe silicate, our observed isotopic fractionations constrain chondrule formation times to approximately 60 min, consistent with previous work. (c) 2006 Elsevier Inc. All rights reserved.
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The dynamics of radiative energy partitioning on drying terrestrial surfaces reflects the strong coupling between evaporation and surface temperature that shapes latent and sensible heat fluxes. We used a new pore-scale analytical...
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The dynamics of radiative energy partitioning on drying terrestrial surfaces reflects the strong coupling between evaporation and surface temperature that shapes latent and sensible heat fluxes. We used a new pore-scale analytical model that explicitly links evaporative fluxes with temperature dynamics of drying surfaces. Model predictions were in good agreement with measured evaporation rates and surface temperature variations observed during drying of a homogeneous sand surface. The model was extended to heterogeneous surfaces by considering responses of representative elements of a complex surface and weighing relative contributions to formulate area-averaged fluxes. Notwithstanding the small scale basis of the model, the fully coupled surface energy balance provides a physically-based framework for predicting the Bowen ratio and the Priestley-Taylor alpha (Priestley and Taylor, 1972) for a range of boundary conditions using readily available input variables (radiation, air temperature, etc.). Analyses show that a is not constant (typically assumed as alpha = 1.26), it decreases with surface drying and increasing net radiation, and increases with increasing wind speed. The physically-based predictability offers new opportunities for generalization of algorithms that rely on remotely sensed surface temperature to estimate surface fluxes. (C) 2014 Elsevier B.V. All rights reserved.
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Terrestrial evaporation is an essential variable in the climate system that links the water, energy and carbon cycles over land. Despite this crucial importance, it remains one of the most uncertain components of the hydrological ...
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Terrestrial evaporation is an essential variable in the climate system that links the water, energy and carbon cycles over land. Despite this crucial importance, it remains one of the most uncertain components of the hydrological cycle, mainly due to known difficulties to model the constraints imposed by land water availability on terrestrial evaporation. The main objective of this study is to assimilate satellite soil moisture observations from the Soil Moisture and Ocean Salinity (SMOS) mission into an existing evaporation model. Our over-arching goal is to find an optimal use of satellite soil moisture that can help to improve our understanding of evaporation at continental scales. To this end, the Global Land Evaporation Amsterdam Model (GLEAM) is used to simulate evaporation fields over continental Australia for the period September 2010-December 2013. SMOS soil moisture observations are assimilated using a Newtonian Nudging algorithm in a series of experiments. Model estimates of surface soil moisture and evaporation are validated against soil moisture probe and eddy-covariance measurements, respectively. Finally, an analogous experiment in which Advanced Microwave Scanning Radiometer (AMSR-E) soil moisture is assimilated (instead of SMOS) allows to perform a relative assessment of the quality of both satellite soil moisture products. Results indicate that the modelled soil moisture from GLEAM can be improved through the assimilation of SMOS soil moisture: the average correlation coefficient between in situ measurements and the modelled soil moisture over the complete sample of stations increased from 0.68 to 0.71 and a statistical significant increase in the correlations is achieved for 17 out of the 25 individual stations. Our results also suggest a higher accuracy of the ascending SMOS data compared to the descending data, and overall higher quality of SMOS compared to AMSR-E retrievals over Australia. On the other hand, the effect of soil moisture data assimilation on the evaporation fields is very mild, and difficult to assess due to the limited availability of eddy-covariance data. Nonetheless, our continental scale simulations indicate that the assimilation of soil moisture can have a substantial impact on the estimated dynamics of evaporation in water-limited regimes. Progressing towards our goal of using satellite soil moisture to increase understanding of global land evaporation, future research will focus on the global application of this methodology and the consideration of multiple evaporation models. (C) 2015 Elsevier B.V. All rights reserved.
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Flat evaporator loop heat pipes with good thermal performance and compact volume have been widely used in electronic device applications. A flat-disk evaporator loop heat pipe made of aluminum alloy was designed for terrestrial ap...
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Flat evaporator loop heat pipes with good thermal performance and compact volume have been widely used in electronic device applications. A flat-disk evaporator loop heat pipe made of aluminum alloy was designed for terrestrial application in this paper. R1233zd(E) was selected as the working fluid for its ultra-low toxicity and environmentally friendly. The pumping force of the system, driving the working fluid circulation, was generated by the sintered capillary wick made from nickel powder. Considering the requirements for electronics and the capillary limit of the wick together, the target temperature was below 75 degrees C and the effective heat transfer length was set as 790 mm. With a heat sink temperature of -10 degrees C, it could dissipate the heat of 190 W (11.43 W/cm2). The performance investigation under bad external conditions was also carried out. A relatively broad operating range between the heat load of 10 W (0.60 W/cm2) and 130 W (7.82 W/cm2) was observed with a 30 degrees C heat sink temperature. However, slight temperature overshoot occurred during the start-up test but the system was able to self-regulate and stabilize quickly. Moreover, the variable heat load test, imitating the heat-dissipating demand for actual electronic devices, demonstrated that this system responded fast and operation failure did not happen. The minimum thermal resistance of the evaporator and the total LHP was 0.134 degrees C/W and 0.197 degrees C/W, respectively.
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