Evaporation Measurements Research Articles

Modeling water fluxes through containerized soilless substrates using HYDRUS

AbstractContainerized crop production can enhance plant health and ensure environmental sustainability, yet proper management requires improved understanding of water fluxes and storage within soilless substrates. Numerical simulation tools developed to simulate water movement in porous media, such as HYDRUS‐3D, may help to quantify effective hydraulic properties of soilless substrates but have not yet been tested in this capacity. Therefore, this study had three main objectives: (a) to assess the accuracy of HYDRUS‐3D for simulating water flow through peat‐ and bark‐based soilless substrates by comparing measured and modeled drainage and water storage; (b) to determine sensitivity of model outputs to individual hydraulic parameters; and (c) to compare model parameterization using three laboratory characterization methods (instantaneous profile sorption, instantaneous profile desorption, and evaporation) vs. inverse modeling with HYDRUS. The results showed that the modeled water contents and drainage timing and amounts were most sensitive to saturated volumetric water content (θs) and least sensitive to saturated hydraulic conductivity (Ks). With regard to parameterization methods, the inverse modeling approach provided the most accurate water balance simulations for both substrates, followed by the sorption method. These two methods estimated lower peak water contents and greater drainage compared with simulations parameterized using desorption and evaporation measurements. Overall, the study results showed that the Richards equation, as calculated using HYDRUS, can provide accurate simulations of water flux through containers when properly calibrated, though sorption‐derived parameters may suffice when model optimization is impractical.

Development of mass-transfer evaporation model for Lake Nasser, Egypt

Abstract Evaporation from free water surface is considered a very important constituent in both the energy and hydrologic cycles. Precise measurement of evaporation from the free water surface is almost impossible. This is why we need a calculation model for free water evaporation. In this study, a simple mass-transfer evaporation model was developed to be applicable over Lake Nasser in the hyper-arid region located in the south of Egypt. Measured meteorological data (2011–2014) at two stations, Aswan and Abu-Simbel, were used to calculate free water surface evaporation using Priestly–Taylor equation. Priestly–Taylor equation was used because it is the most appropriate equation for Lake Nasser evaporation according to the literature. Results from this model were used to develop a simple mass-transfer evaporation model. The statistical analysis for both calibration and validation periods were very good. The slope of the regression line is about 0.9, with a coefficient of determination of 0.98. The t value is 0.6, at p value of 0.544, which is much greater than 0.05. The developed model could be used with confidence at Aswan meteorological station or on the average of the two meteorological stations, while it should be used carefully on Abu-Simbel meteorological station.

Estudio del proceso de evaporación en el Salar Tres Quebradas por medio de medidas in situ y datos de satélite

<p>The calculation of evaporation (<em>Ev</em>) is a fundamental process on the planning of investment for nonmetallic mining in salt flats. Dispose to reliable estimates of evaporation allows to reduce one of the main uncertainties of the flow models in this type of basin. This paper focuses on the calculation of <em>Ev</em> in the Tres Quebradas salt flat, Catamarca (Argentina), applying Priestley-Taylor model whit satellite data. Study area comprises the Tres Quebradas and Verde lagoons, and a central evaporite zone. Satellite data (CERES and OLI-LandSat 8), meteorological information, brine density measurements, evaporation measurements, and spectral signatures to calculations were used. The lagoons evaporation was estimated and by means of a Class A evaporation pan validated. The evaporation control in evaporite zones also was studied using a phreatic level function. <em>Ev</em> values of 1302 mm year<sup>–1</sup> and 1249 mm year<sup>–1</sup> for the Tres Quebradas and Verde lagoons were obtained, respectively, similar to Class A evaporation pan values measured. In the case of evaporite zones, an average annual value of 152 mm year<sup>–1</sup> was estimated, regulated by the phreatic level. In summary, an average annual of system water loss by evaporation of 1.31±0.32 m<sup>3</sup> s<sup>–1</sup> was obtained, where more than 80% corresponds to the Tres Quebradas and Verde lagoons, and the rest to the central evaporite zone. The results achieved are consistent and will be used as input data in the numerical flow modeling to the estimation of the lithium brine reserve of the salt flats.</p>

Approaches to scheduling water allocations to kikuyugrass grown on a water repellent soil in a drying-climate

Water allocation is a principal planning method for managing water supplies to agricultural and horticultural land in drying climates. Regulatory bodies often establish the water allocation amount, but its distribution during the irrigation season is left to the land manager’s discretion. We evaluated approaches to best manage water allocations to a warm-season turfgrass [Pennisetum clandestinum (Holst. Ex Chiov)] grown on a free-draining sand prone to surface (0–25 mm) soil water repellence in a Mediterranean climate in south-western Australia under ‘deficit irrigation’, in a two-year field study. The three factorial experiment consisted of three levels for each treatment applied to plots (10 m2) of kikuyugrass: water allocation (5000, 6250 or 7500 kL ha−1 yr−1), irrigation schedule, and soil wetting agent rate (nil, recommended ‘label’ rate, double recommended ‘label’ rate), and was replicated three times. The irrigation schedules were based on historical net evaporation at the site, and then refined monthly using in-season net evaporation data or measurements of soil water content. Kikuyugrass growth and color was adequate when irrigated using the current regional water allocation (7500 kL ha−1 yr−1) under a low wear situation and to a lesser extent when the water allocation was lowered to 6250 kL ha−1 yr−1. Application of a soil wetting agent diminished water repellence and improved kikuyugrass color for 7500 or 6250 kL ha−1 yr−1 water allocations. Distributing a water allocation based on historical monthly net evaporation rates was a simple and effective scheduling approach to maintaining a warm-season turfgrass.

Measurement of evaporation of hydrocarbon droplets by laser absorption spectroscopy

Concentration measurements of evaporated hydrocarbon species by infrared laser absorption spectroscopy at a monodisperse droplet chain are presented. A droplet generator was installed within a flow channel and operated with cyclohexane, iso-octane, n-heptane, n-pentane and 1-butanol. The flow channel was flushed with a laminar flow of air at different temperatures. The absorption of a HeNe laser beam at $$\lambda = 3.39\,\upmu \hbox {m}$$ traversing through the flow channel at varying distances from the droplet chain was exploited to determine the vapor concentrations of the hydrocarbons. Measurements of the absorption cross sections in a heated gas cell ($$T = 300$$–773 K) enabled the quantification of the absorption signals from the droplet chain. Vapor concentrations were determined in planes perpendicular to the droplet chain. From the increase of vapor concentration between the planes, the evaporation rate could be determined. The evaporation rates were measured in dependence of co-flow temperature, droplet velocity, droplet generation frequency and droplet spacing. In the investigated temperature range of the air (313–430 K) the evaporation rates increased linearly with temperature. The order of the fuels with respect to evaporation rates corresponded with the boiling points of the individual fuels. In addition to the presentation of the results, the paper discusses the performance of vapor concentration measurements by laser absorption spectroscopy at droplet chains which has not been tested before in such a configuration. Particular attention was paid to the spatial resolution of the measurement. The results are well suited to validate models and numerical simulations.

A study of the drying behaviour of various types of hydrated hydroxypropyl cellulose (HPC) and their mixtures with drugs of different solubility using DSC

The objective of this research was to interpret the drying behaviour of hydrated hydroxypropyl cellulose (HPC) types HF, MF, LF and their blends (1:1 w/w) composed of drugs with low solubility as salicylic acid and high solubility as sodium salicylate. Polysaccharides differed significantly in their molecular mass and viscosity. The evaporation measurements were carried out using differential scanning calorimetry. The dry mass normalized dependency of vaporization enthalpy (ΔH) and respective contents of water Wc (water fraction in the dry mass of sample) ΔH = f(Wc) were linear. The sought values of water associated with the evaporation process (Nev) were calculated after extrapolation ΔH to 0. The obtained data confirmed earlier results that Nev values are not directly related to molecular weight of the polymer, because they were equal to 0.11 g g−1 for all raw types of HPC. Poorly soluble salicylic acid slightly increased the Nev content to 0.11–0.15 g g−1. A higher increase in the Nev content was observed for matrices composed of sodium salicylate and was ranging from 0.16 to 0.27 g g−1. For all types of raw HPC, it was concluded that beside the non-freezing water bound to sorption sites, there is a part of water restricted in temporary pores. In the case of studied mixtures, the non-freezing water consists mostly of water molecules interacting with sorption sites not trapped in pores. A slightly higher content of Nev calculated for HPC and sodium salicylate mixtures could be explained by the fact of stronger interaction between the dissociated ion pair of sodium salicylate and water molecules.

PSIII-36 Increased viscosity enhances water intake and reduces risk of calcium oxalate stone formation in cats

Abstract The control of liquid intake in cats is especially of interest as there is a significant risk of urinary tract stone formation due to their high urinary solute density. Calcium oxalate stone formation is not easily mitigated by dietary manipulation. This study investigated if increasing water viscosity (282 vs 2.9 centipoise; means throughout are viscous water followed by control cats) improved voluntary intake of water and calcium oxalate stone risk. Twelve cats (7 neutered males, 5 spayed females) from 3 to 8 years of age with an average weight 4.7 kg were monitored for 4 months. Each cat spent 2 months consuming viscous water and two months consuming normal water in a crossover design. Water consumption was measured through loss of weight from each pet’s water bowl with an additional bowl of the consumed viscosity placed in the room for evaporative loss measurements. A urine calcium oxalate titrimetric test (COT) was performed to evaluate the risk of calcium oxalate stone formation. In brief, the [Ca+2]/(added Oxalate-2) ratio is calculated (per liter). An increasing index value denotes samples at greater risk of calcium oxalate crystallization. The ratio represents the concentration of ionized calcium and the amount of oxalate that is added to initiate crystallization. The results showed that cats drinking viscous water had a significant increase in water consumption (79.9 vs 65.6 grams P = 0.014). There was a reduction in urine specific gravity (1.042 vs 1.052 P = 0.016), fractional excretion of calcium (0.197 vs 0.280 P = 0.036), urinary calcium concentration (49.8 vs 61.8 ppm P < 0.01) and in stone risk as measured by COT (35.5 vs 82.4 P = 0.029). In conclusion, these data show that there is an increased intake of water when cats are offered water with increased viscosity and increased viscosity was associated with an improvement in measurements of oxalate stone risk.

Partitioning evapotranspiration and its long-term evolution in a dry pine forest using measurement-based estimates of soil evaporation

The future of forests and their productivity in dry environments will depend on both water availability through precipitation and ecosystem and plant water use characteristics. It is increasingly recognized that better understanding water use patterns and their response to change depends on our ability to partition evapotranspiration (ET). Here, we use chamber-based direct measurements of soil evaporation (Es) in a semi-arid Pinus halepensis forest to partition ET to Es and tree transpiration (Et), to assess the daily and seasonal changes and to compare annual-scale values with measurements carried out at the same site ten years earlier. The ecosystem is characterized by a high annual Es/ET ratio of 0.26, and an Et/ET of 0.63. Es diminished in the long dry season, but as much as 74 ± 5% of the residual flux was due to the re-evaporation of nighttime moisture adsorption, which may provide critical protection from soil drying. Over the 10 years observation period concurrent increase in the transpiration ratio (TR=Et/ET; +29%) and in leaf area index (LAI; +44%) were observed, with the ratio of TR/LAI remaining constant at ~0.31, and with persistently closed hydrological balance (ET/P of 0.94–1.07). The observed Et/ET values are similar to the estimated global mean values, but are attained at a much higher aridity index (5.5) than the mean one, demonstrating the potential for expanding forestation into dry regions.

Quantifying the contribution of riparian total evaporation to streamflow transmission losses: Preliminary investigations along the Groot Letaba river

The Groot Letaba River, situated in the semi-arid north-eastern region of South Africa is an example of a river system in which the uncertainty associated with transmission losses (TL) has limited the effective management of environmental water requirement (EWR) flows. TL along the river significantly impacts EWR flows, as it is often the case that specified EWR releases are not adequately received further downstream. Due to the limited understanding of the magnitude of TL, as well as the dominant contributing processes to TL within the region, it remains a challenge to operate the river using downstream targets far from the source of operations. In an attempt to address this knowledge gap, detailed characterizations of hydrological processes were performed along the lower reaches of the river, which centred around the estimation of riparian total evaporation and quantifying the rapport between surface and subsurface water flow processes. Riparian total evaporation was estimated using the satellite-based surface energy balance system model, soil water evaporation measurements and open water evaporation estimates. Losses from the river to the adjacent aquifer were determined from the continuous monitoring of the groundwater phreatic surface and characterization of aquifer hydraulic properties. The results of these investigations indicated that present flows within the system are likely to be insufficient to satisfy gazetted median and extreme low flow targets. Overall, the study details key hydrological processes influencing TL along the river. It should, however, be noted that these observations only provide an understanding of the system over a limited observation period.

Effect of Decreased Temperature on the Evaporation of α-Pinene Secondary Organic Aerosol Particles

Interplay of volatility distribution and particle viscosity governs the gas-to-particle partitioning dynamics of atmospheric secondary organic aerosol (SOA) constituents. Temperature-induced shifts in both particle volatility distribution and viscosity can influence the evaporation behavior of atmospheric SOA particles. However, knowledge of the particle evaporation at low temperatures is still limited. Here, we combined the isothermal evaporation measurements and processes modelling to explore the evaporation of α-pinene ozonolysis (αpinO3) and photooxidation (αpinOH) SOA particles under a series of relative humidity (RH) at two different temperatures. Experimental results revealed that the particle evaporation was hindered at low temperature, in agreement with the temperature dependence of the effective saturation vapor concentration and the possible temperature impact on the particle viscosity. Both αpinO3 and αpinOH SOA particles showed similar evaporation rates at 80% RH when particles were in a liqu...

Measurement of transient evaporation of an ethanol droplet stream with phase rainbow refractometry and high-speed microscopic shadowgraphy

Quantifying the evaporation rate of droplets is of great importance in many applications and this is especially true if the evaporation occurs in a rapidly changing environment, such that models describing evaporation under steady state conditions are no longer valid. To achieve such information from experiments, the phase rainbow refractometry (PRR) technique has recently be shown to be capable of simultaneously measuring temperature, size, and size variation at the nanometer scale, quantities essential for quantifying transient evaporation rates. The present study examines the use of the PRR technique to characterize the evaporation of monodispersed droplets in a droplet stream injected into ambient air. This is combined with high-speed microscopic shadowgraphy, yielding as measured quantities droplet diameter, diameter change, temperature evolution, velocity and computed transient evaporation rate of the droplet stream. The accuracy and resolution of the measurements are evaluated by comparison with theoretical values and values measured with alternative means. Furthermore, the results are used to investigate how the evaporation rate is modified by interaction among droplets in the droplet stream and how these rates differ from evaporation rates predicted for isolated droplets, using the well proven Abramzon and Sirignano model. Finally, the evaporation rate, including the influence of droplet interaction, is shown to be in line with correlations suggested by Virepinte; refinement to this correlation is proposed.

Predicting soil water balance for irrigated and non-irrigated lucerne on stony, alluvial soils

•Efficient use of irrigation is essential for minimising environmental impacts of agriculture, particularly on stony soils which are vulnerable to nitrogen leaching. Models of soil water balance are essential tools for effective agricultural water management. Here we use the soil water flow model HYDRUS-1D to predict evaporation, total 1.5 m soil profile water content, and drainage at 1.5 m soil depth for irrigated and non-irrigated lucerne (Medicago sativa L.) on stony, alluvial soils in central South Island, New Zealand. Modelled estimates were compared against measurements of evaporation by eddy covariance, profile soil water content from soil moisture sensors, and drainage from lysimeters from 1 October 2016 to 1 July 2018 at each site. Cumulative evaporation and drainage were within 4% of measurements and short-term variations were well predicted for non-irrigated lucerne. Under irrigation, modelled cumulative evaporation and drainage overestimated measurements by 6 and 24% respectively. This overestimation must be viewed within the context of uncertainties related to the measurements, particularly given non-closure of the measured water balance related to spatial variability and inherent biases in the measurement methods. Model inputs and concept are likewise sources of uncertainty. Total water content predicted for the 1.5 m depth soil profile was 40–50% greater than the measured volume for both non-irrigated and irrigated lucerne, although short term variations were well predicted, suggesting that further research is needed on estimation of soil hydraulic parameters which represent water storage in these stony, alluvial soils. Our results highlight the value of well-measured sites, such as those of the current study, for evaluating the quality of soil hydrological predictions.

Multi-station artificial intelligence based ensemble modeling of reference evapotranspiration using pan evaporation measurements

In this study, different Artificial Intelligence (AI) techniques including Feed Forward Neural Network (FFNN), Adaptive Neuro Fuzzy Inference System (ANFIS), Support Vector Regression (SVR), empirical models including Hargreaves and Samani (HS), Modified Hargreaves and Samani (MHS), Makkink (MK), Ritchie (RT) and conventional Multilinear Regression (MLR), were employed to model Reference Evapotranspiration (ET0) in fourteen stations from several climatic regions in Turkey, Cyprus, Iraq, Iran and Libya. For this purpose, 12 parameters of monthly climate data were collected and used as input parameters to the models. The parameters were subjected to quality assurance tests to ensure their validity and acceptability. The study was conducted in three sections: (i) Sensitivity analysis was conducted to determine the dominant inputs. (ii) Single models were trained and their performances were accessed on the basis of ET0 derived from pan evaporation method. (iii) Finally, three ensemble methods of simple averaging, weighted averaging and neural ensemble were applied in strategy 1 (for AI models) and strategy 2 (for empirical models) to improve the predicting performance. The results revealed that depending on the climate of the regions, pan evaporation, solar radiation, temperatures and surface pressure are the most dominant parameters, empirical and MLR models could be employed to achieve the valuable results, AI based models are superior in performance to the other models, also promising improvement in ET0 modeling could be achieved by ensemble modeling. The results of this study affirmed that the provided ensemble approaches can increase the performance of single models in the verification phase up to 22%, for strategy 1 and 55%, for strategy 2. Also, the results demonstrated that AI based ensemble modeling is preferable to empirical ensemble modeling.

Method to Measure Area Specific Resistance and Chromium Migration Simultaneously from Solid Oxide Fuel Cell Interconnect Materials

AbstractChromium evaporation is identified as a major degradation mechanism in solid oxide fuel cell (SOFC) stacks. The major chromium source is the commonly used stainless steel interconnects, thus raising a need for protective coatings on the interconnect steel. Ex situ characterization methods of protective coatings involve chromium evaporation measurements, area specific resistance (ASR) measurements and long‐term exposure tests. To replicate stack conditions, commonly used ASR measurement setups should be further developed. This work presents an improved characterization method for steels and coatings and aims to be an extension to state‐of‐the‐art characterization methods. The studied steel samples, bare or coated, are placed adjacent to palladium foils with a screen‐printed lanthanum‐strontium‐cobalt (LSC) layer and the resistivity over the pair is measured. The method offers similar contact materials, chromium migration mechanisms, electrical contacts and chemical interactions, as seen in stacks. Further, it enables post‐test chromium migration analysis with electron microscopy. Demonstration of the method validated that protective coatings hindered both oxidation and chromium migration from the substrate steels. The presented method could aid in accelerating protective coating development.

The utility of thermal satellite images and land-based meteorology to estimate evaporation from large lakes

Evaporation measurements over lakes are limited by physical constraints, logistics and financial demands. Thermal satellite images and land-based meteorology can be combined to derive evaporation rates from large lakes. The Dead Sea is a large hypersaline lake that can be used to examine the utility of thermal satellite images along with land-based meteorology to assess evaporation rates. Sea surface tmperature was retrieved for a 12-month period using band 10 onboard Landsat 8. Monthly SST was combined with nearby land-based meteorology to estimate evaporation from the sea surface using a mass transfer method and two variations of the Penman procedure. The Mass transfer gave an annual evaporation rate of 1005 mm whereas the Penman and the Priestley-Taylor methods gave 1308 and 1140 mm, respectively. These values are commensurate with extensive field measurement and theoretically derived evaporation values. Analysis shows a tradeoff between wind speed increase over the smoother lake surface and the drop in the saturation water vapor pressure deficit across the lake-atmosphere boundary. Wind speed has profound effects on evaporation differences during the warm season but diminish appreciably in the cold season when the vapor pressure deficit is small. Thermal images were able to resolve the presence of large pockets of cool water over the Dead Sea resulting from freshwater input. Modifications to evaporation caused by freshwater input to a hypersaline lake are investigated from a thermodynamic perspective. The alteration to evaporation depends on the simultaneous departure of surface temperature and the activity of the brine.

Graphene Oxide Carburization Enhanced Ionization Efficiency for TIMS Isotope Ratio Analysis of Uranium at Trace Level.

Isotope analysis of trace uranium is important in nuclear safeguards and nuclear forensics, which requires the analytical methodologies with high sensitivity, accuracy, and precision. As one of the most powerful techniques in isotopic measurement, thermal ionization mass spectrometry (TIMS) usually suffers from its relatively low sensitivity in ultratrace measurements. To overcome this limitation, we have developed a new filament carburization technique for TIMS, with graphene oxide (GO) as the ionization enhancer. A high and steady ionization efficiency of ∼0.2% for uranium was achieved in single-filament mode, which was 10× the classical double-filament method. With total evaporation (TE) measurements, this method was validated with certified reference materials (CRMs) at the picogram level, and the relative uncertainties for n(235U)/ n(238U) were as low as the ∼1% level. The enhancement mechanism of GO's promoting effect on uranium ionization was attributed to the uniform microstructure facilitating energy transfer and formation of carbides. This approach provides an alternative simple and rapid method for trace uranium isotope analysis with high sensitivity and excellent repeatability. Filament carburization and uranium loading could be accomplished within 10 min. This technique has great advantage in analysis of trace uranium isotope ratios and can be applied in the researches of environmental analysis and nuclear forensics.

Estimation of monthly pan evaporation using support vector machine in Three Gorges Reservoir Area, China

Pan evaporation plays a critical role in estimating water budget and modeling crop water requirements. However, it has been measured at a very limited number of meteorological stations. Estimation of pan evaporation from measured meteorological variables offers an important alternative and drawn increasing attention in the recent years. This paper investigated the performance of support vector machine (SVM) in the estimation of monthly pan evaporation using commonly measured meteorological variables in Three Gorges Reservoir Area in China. Evaluation suggested that SVM models showed remarkable performances and significantly outperformed the empirical model. The SVM model with polynomial as kernel function outperformed that with radial basis function. In the case of unavailable measurements of pan evaporation and meteorological variables to construct the SVM model, pan evaporation can be well-estimated by SVM model developed using data at other sites. The results indicated that the SVM method would be a promising alternative over the traditional approaches for estimating pan evaporation from measured meteorological variables.

Initial operation of the recoil mass spectrometer EMMA at the ISAC-II facility of TRIUMF

The Electromagnetic Mass Analyser (EMMA) is a new vacuum-mode recoil mass spectrometer currently undergoing the final stages of commissioning at the ISAC-II facility of TRIUMF. EMMA employs a symmetric configuration of electrostatic and magnetic deflectors to separate the products of nuclear reactions from the beam, focus them in both energy and angle, and disperse them in a focal plane according to their mass/charge (m/q) ratios. The spectrometer was designed to accommodate the gamma-ray detector array TIGRESS around the target position in order to provide spectroscopic information from electromagnetic transitions. EMMA is intended to be used in the measurement of fusion evaporation, radiative capture, and transfer reactions for the study of nuclear structure and astrophysics. Its complement of focal plane detectors facilitates the identification of recoiling nuclei and subsequent recoil decay spectroscopy. Here we describe the facility and report on commissioning efforts.

On Condensation and Evaporation Mechanisms in Disordered Porous Materials.

Sorption isotherm measurement is a standard method for characterizing porous materials. However, such isotherms are generally hysteretic, differing between condensation and evaporation. Quantitative measurement of pore diameter distributions requires proper identification of the mechanisms at play, a topic which has been and remains the subject of intensive studies. In this paper, we compare high-precision measurements of condensation and evaporation of helium in Vycor, a prototypical disordered porous glass, to a model incorporating mechanisms on the single pore level through a semimacroscopic description and collective effects through lattice simulations. Our experiment determines both the average of the fluid density through volumetric measurements and its spatial fluctuations through light scattering. We show that the model consistently accounts for the temperature dependence of the isotherm shape and of the optical signal over a wide temperature range as well as for the existence of thermally activated relaxation effects. This demonstrates that the evaporation mechanism evolves from pure invasion percolation from the sample's surfaces at the lowest temperature to percolation from bulk cavitated sites at larger temperatures. The model also shows that the experimental lack of optical signals during condensation does not imply that condensation is unaffected by network effects. In fact, these effects are strong enough to make most pores to fill at their equilibrium pressure, a situation deeply contrasting the behavior for isolated pores. This implies that, for disordered porous materials, the classical Barrett-Joyner-Halenda approach, when applied to the condensation branch using an extended version of the Kelvin equation, should properly measure the true pore diameter distribution. Our experimental results support this conclusion.

Field quantification of the water footprint of an apple orchard, and extrapolation to watershed scale within a winter rainfall Mediterranean climate zone

Field scale quantifications of the water footprints (WF) of crops, based on actual measurements, provide valuable and detailed information for on-farm water use management. However, watershed-based WF assessments are more appropriate for large-scale water resources management beyond the farm boundaries. In this study, blue, green and grey WF information, using the Water Footprint Network approach up to farm gate level, was determined for an apple (Malus pumila) orchard growing under Mediterranean climate conditions in South Africa. WFblue and WFgreen were determined through measurements of transpiration, total evaporation, rainfall, irrigation and other operational water uses, and WFgrey was calculated from fertilizer applications. Combined field-scale blue/green/grey water footprint data were extrapolated to watershed scale by means of representative monthly FAO-56 type reference potential evaporation (ETo) values and crop coefficients derived from the field scale observations. Resultant water use values were converted to a volumetric equivalent by multiplying by the area under apple orchards in each watershed. The volumetric equivalents were then summed for all QCs in the Water Management Area to calculate the overall water footprint for apple production in the basin. Orchard-scale WF, taking into account all water uses and a fruit yield of 61.5 t.ha−1, was 212.1 m3. t−1, comprising 62.7% WFblue, 14.9% WFgreen and 22.5% WFgrey. Irrigation thus contributed the bulk of the WF in the apple production chain. Resultant water productivity (WP) figures for the orchard averaged 4.72 kg.m¯³. Scaling up the WF estimates to QC level gave an average value of 228.4 m3. t−1 (WP = 4.41 kg.m¯³). Accurate crop coefficients, representative weather / ETo data and reliable crop areas within each QC are critical requirements in terms of upscaling WF estimates, where the information has potential application in water allocation decisions, Water-Energy-Food (WEF) Nexus cost-benefit analyses and other water resource management decisions.