Daily Evaporation Rate Research Articles

Simulated water fluxes during the growing season in semiarid grassland ecosystems under severe drought conditions

summary To help improve understanding of how changes in climate and land cover affect water fluxes, water budgets, and the structure and function of regional grassland ecosystems, the Grassland Landscape Productivity Model (GLPM) was used to simulate spatiotemporal variation in primary water fluxes. The study area was a semiarid region in Inner Mongolia, China, in 2002, when severe drought was experienced. For Stipa grandis steppe, Leymus chinensis steppe, shrubland, and croplands, the modeled total, daily and monthly averaged, and maximum evapotranspiration during the growing season and the modeled water deficits were similar to those measured in Inner Mongolia under similar precipitation conditions. The modeled temporal variations in daily evaporation rate, transpiration rate, and evapotranspiration rate for the typical steppes also agreed reasonably well with measured trends. The results demonstrate that water fluxes varied in response to spatiotemporal variations in environmental factors and associated changes in the phenological and physiological characteristics of plants. It was also found that transpiration and evapotranspiration (rather than precipitation) were the primary factors controlling differences in water deficit among land cover types. The results also demonstrate that specific phenomena occur under severe drought conditions; these phenomena are considerably different to those occurring under normal or well-watered conditions. The findings of the present study will be useful for evaluating day-scale water fluxes and their relationships with climate change, hydrology, land cover, and vegetation dynamics. 2014 Published by Elsevier B.V.

The impact of taro (Colocasia esculenta) cultivation on the total evaporation of aCyperus latifoliusmarsh

Total evaporation (ET) is one of the major components of the water budget of a wetland. Very little research has been conducted on the loss of water to the atmosphere from different wetland vegetation types occurring in southern Africa. This study on the ET of taro (locally known as madumbe) and sedge within the Mbongolwane wetland was conducted to assess the potential impact of madumbe cultivation on the hydrology of the wetland. Sugarcane planted on the contributing catchment outside the wetland was the other crop examined. Two field campaigns were conducted in November 2009 and January 2010 during the growing season of the madumbe crop to quantify ET rates in the Mbongolwane wetland and from sugar cane in the surrounding catchment. ET was measured over two vegetation types in the wetland, namely: madumbe (Colocasia esculenta); sedge (Cyperus latifolius) with some reeds (Phragmites australis); and sugarcane in adjacent terrestrial areas. ET from the madumbes ranged from 1.0 to 6.0 mm day−1. The daily average ET rates in November 2009 were 3.5 and 4.9 mm for the madumbe and sedge sites, respectively, and 4.0 mm for sugarcane grown in the catchment. The daily average ET rates in January 2010 were 3.3 and 3.7 mm for the madumbes and sedge sites, respectively, and 2.4 mm for the sugarcane site. The daily ET was therefore lower at the madumbe site in November 2009 and in January 2010 compared to the sedge site. An average crop factor of 0.6 was obtained from this study during the growth stage of the madumbes. Copyright © 2012 John Wiley & Sons, Ltd.

The energy and water balance of a Eucalyptus plantation in southeast Brazil

The eddy covariance method was used to measure energy and water balance of a plantation of Eucalyptus ( grandis × urophylla ) hybrids over a 2 year period. The average daily evaporation rates were 5.4 (±2.0) mm day −1 in summer, but fell to 1.2 (±0.3) mm day −1 in winter. In contrast, the sensible heat flux was relatively low in summer but dominated the energy balance in winter. Evaporation accounted for 80% and 26% of the available energy, in summer and winter respectively. The annual evaporation was 82% (1124 mm) and 96% (1235 mm) of the annual rainfall recorded during the first and second year, respectively. Daily average canopy and aerodynamic conductance to water vapour were in the summer 51.9 (±38.4) mm s −1 and 84.1 (±25.6) mm s −1 , respectively; and in the winter 6.0 (±10.5) mm s −1 and 111.6 (±24.6) mm s −1 , respectively.

Possibility of mapping physiographic zones by thermal survey from space

Physiographic zones of the Earth are “major units of the geographic (landscape) sphere, which give way to each other in a regular and definite order depending mainly on the ratio of heat and moisture” [1]. The rise in the Earth’s annual mean temperature recorded for the instrumental observation period [2] may provoke variations in the global distribution of the heat/moisture ratio and, as a consequence, in displacement of the position and configuration of physiographic zones. The variations may be accompanied by negative socioeconomic impacts. To minimize the negative consequences, it is expedient to carry out a timely forecasting based on data of the space monitoring of physiographic zones. Such monitoring requires analysis of a giant body of data. Therefore, it is necessary to elaborate automatic methods for the mapping of these zones by using satellite-borne survey. Currently, several quantitative criteria (indices) have been suggested to identify physiographic zones, e.g., Budyko’s radiational aridity index [3], which characterizes the ratio between the annual radiation balance and annual precipitation. The space version of this method is limited by the need for obtaining continuous yearlong series of observations over elements of the radiation balance of the day surface and atmospheric precipitation. Cloudiness prevents the recording of such continuous series. Therefore, we have studied the possibility of applying another method for monitoring the position of physiographic zones, namely mapping of the thermal inertia of the Earth’s surface based on a satellite-borne thermal survey data [4‐11]. 1 1 Thermal inertia p is the resistance of a surface to heating (or cooling) under the influence of a periodic heat source. p = ( λ · c · ρ ) 1/2 , J/(m 2 · s 1/2 · K) = 1 TIU, where λ is the thermal conductivity factor, W/(m · K); c is specific heat, J/(kg · K), and ρ is density, kg/m 3 . The method we applied for the remote mapping of thermal inertia (TI); daily mean evaporation rate (ER) from the Earth’s surface, mm/day; and heat flux (HF), W/m 2 involved the mathematical model of the daily variation of the Earth’s surface temperature (ESTs) [10], which took into account basic factors affecting the EST formation. The model has the following assumptions: the metrological conditions and concentration of optically active gases in the atmosphere within the whole area under study are identical; emittance, albedo of the Earth, and TI do not vary during the whole period of the satellite-borne thermal survey. To determine TI and ER, we carried out the thermal multispectral space survey for 3‐10 days under stable meteorological conditions in the absence of rainfall in order to characterize the daily EST dynamics more completely. Moreover, mapping of TI and ER was based on the following parameters of routine expedited meteorological observations over parameters involved in the mathematical EST model: total solar radiation; air temperature, moisture, and wind velocity at a height of 2 m above the surface; atmospheric pressure; and cloudiness. To solve the inverse problem, we performed mathematical EST modeling for all possible combinations of TI, ER, HF, and albedo, i.e., the “library” of ideal ESTs. Then, the measured EST values were compared to ideal values. The TI and ER values sought were deduced from the assigned fitting criterion of measured and ideal EST values. Algorithm errors of solving the inverse problem are given in the table.

Efficiency of shading materials in reducing evaporation from free water surfaces

The aim of this study was to characterize the influence of various shading materials on the evaporation rate from a Class-A pan and on its driving variables. Hourly evaporation measurements from two pans, one uncovered and the other covered with different types of shading meshes, were carried out under summer conditions, along with measurements of air temperature and humidity, water temperature, solar global radiation and wind speed. Single and double-layered polyethylene meshes of different colours and a single layered aluminized mesh were tested. The aerodynamic and shading effects responsible for the evaporation reduction, as well as the additional processes of condensation and water recovery, were analyzed and discussed. In all cases, shading the pan induced a significant decrease of the daily evaporation rate, ranging from 50% for the aluminized screen to near 80% for the coloured-polyethylene meshes. The latter materials combined an efficient aerodynamic effect (decrease of about 70% of the mass transfer coefficient) with a strong diminution of surface-to-air water vapour gradient. The condensation over the meshes was far for being negligible for the black polyethylene meshes, reaching up to 15–20% of the daily evaporation losses. It was concluded that the choice of the shading material should be based on criteria related to porosity and optical properties, but also to the capacity of the material in enhancing the condensation process during the night and collecting the condensed water. The extrapolation of the results to the case of agricultural water reservoirs was discussed, and an economic analysis was carried out to assess the viability of shading covers under the conditions of water use and pricing prevailing in Southern Spain.

Energy Fluxes of an Open Water Area in a mid-Latitude Prairie Wetland

Concurrent measurements of the surface energy balance components (net radiation, heat storage, and sensible and latent heat fluxes) were made in three communities (open water, Phragmites australis, Scirpus acutus) in a wetland in north-central Nebraska, U.S.A., during May-October, 1994. The Bowen ratio – energy balance method was used to calculate latent and sensible heat fluxes. This paper presents results from the open water area. The heat stored in water (G) was found to play a major role in the energy exchange over the water surface. During daytime, G consumed 45–60% of Rn, the net radiation (seasonally averaged daytime G was about 127 W m−2). At night, G was a significant source of energy (seasonally averaged nighttime G was about -135 Wm−). The diurnal pattern of latent heat flux (λ E) did not follow that of Rn. On some days, λ E was near zero during midday periods with large Rn. The diurnal variability in λ E seemed to be significantly affected by temperature inversions formed over the cool water surface. The daily evaporation rate (E) ranged from 2 to 8 mm during the measurement period, and was generally between 70 and 135% of the equilibrium rate.

Amounts of winter or summer rain triggering germination and ‘the point of no return’ of seedling desiccation tolerance, of some Hordeum spontaneum local ecotypes in Israel.

In this study we observed an important interrelationship between the ability of Hordeum spontaneum C. Koch (Poaceae) seeds to germinate after a small rainfall in winter and the dehydration tolerance of young seedlings after one, two or three weeks in dry conditions. In winter, local ecotypes of H. spontaneum started to germinate after only 10 mm of ‘rain’, when temperatures were mild, daily evaporation rates were low, and soil water content was 5.8%. In summer, however, germination was not triggered until at least 50 mm of ‘rain’ was received, at higher temperatures, evaporation rates and soil water content. The ‘point of no return’ is the earliest stage of germination or after germination at which dehydration will cause the death of the seedling and it depends on the duration in a dry environment, root length before desiccation and on the ecotype. Seedlings were stored in dry conditions for one, two or three weks and then rewetted. A higher percentage of seedlings which had developed roots of 5–20 mm long before desiccation, developed adventitious roots than that of seedlings with roots 1–4 or 40–50 mm long before desiccation. The strategy of regulating germination according to different amounts of rainfall, depending on the season, and seedling drought tolerance, are important survival adaptations in arid and semi-arid regions. These adaptations may enable the young seedlings to overcome drought periods between rainfalls.

DIURNAL EVAPORATION FROM FRESH AND HYPERSALINE SHALLOW PONDS IN A HOT, DRY ENVIRONMENT

A numerical procedure is developed to evaluate the diurnal trend of evaporation from a shallow freshwater pond and a hypersaline pond, both of which are 2 m deep and encountering identical meteorological forcings. Evaporation from both water bodies is calculated using Penman-Brutsaert formulation in which atmospheric buoyancy is calculated based on the semi-empirical theory of Monin-Obukhov formulation. A new iterative procedure is presented in this paper to solve for the water temperature. The present model attains a rapid convergence and compares favorably with temperature and evaporation observations obtained for a hypersaline pond and deep sunken pans. Calculations show that the average daily evaporation rates from the hypersaline pond during January and July are 0.5 and 6.4 mm day-1. Corresponding values for the freshwater pond are 2.4 and 10.45 mm day-1, respectively. Salinity suppresses evaporation strongly during winter because of its coupling effects on net radiation and saturation vapor pressure. During summer, energy availability accounts for 74% and 64% of total diurnal evaporation from the hypersaline pond and freshwater, respectively. In winter, however, the aerodynamic term accounts for about 80% of evaporation from both water bodies. Heat storage/release within the underlying sediments appears to be negligibly small and may be neglected with very little loss of accuracy when formulating the energy balance of shallow lakes. [Key words: evaporation, buoyancy, hypersaline solutions, Dead Sea, energy balance.]

Desorption and the two Stages of Drying of Natural Tallgrass Prairie

During the First ISLSCP (International Satellite Land Surface Climatology Project) Field experiment (FIFE) the first stage of drying (with the atmosphere controlling) in these natural grasslands occurred when the soil was moist with a volumetric soil moisture content SM >27% after rainfall. Both at the local scale and at the regional scale, once SM in the top 10 cm of the soil dropped below about 17% and its vertical gradient started to exceed about 1.1%/cm at 5 cm, the cumulative daily evaporation rate could be taken to be proportional to the square root of time, t½, which is not unlike a second stage of drying (with the soil moisture content controlling). Between these two drying stages, there was a transition period which lasted from several days to 2 weeks depending on the soil moisture conditions and on the season. The longer transition periods were observed under conditions of lower net radiation and of higher soil moisture content at depths in excess of, say, 50 cm. The present findings of gradual transitions from the first stage to a desorptive second stage of drying for a surface covered with grass (which can extract water from greater depths) are in contrast to earlier findings of relatively abrupt transitions for bare soil.

Measured and Simulated Surface Soil Drying

AbstractThe USDA initiated the Wind Erosion Prediction System (WEPS) to develop improved technology for predicting wind erosion. A HYDROLOGY submodel has been developed for WEPS to simulate the soil energy and water balances. This study was conducted to evaluate the performance of the HYDROLOGY submodel in predicting surface soil drying. Water content was measured gravimetrically in a bare 5‐ by 30‐m plot for 14 d after irrigation during July and August 1991. The plot was located 5 m directly north of a bare weighing lysimeter at the USDA‐ARS Conservation and Production Research Laboratory at Bushland, TX. Hourly samples were taken from depth increments of 0 to 2, 2 to 6, 6 to 10, 10 to 30, and 30 to 50 mm. Furthermore, soil cores were taken to 900 mm at 6‐h intervals. Water content was also measured daily at the lysimeter and between the lysimeter and gravimetric sampling plot using a neutron probe to 2.1 m. The submodel accurately predicted that no deep percolation occurred throughout the simulation period. Simulation results agreed well with the measured daily evaporation rates from the lysimeter (r2 = 0.96). Furthermore, the submodel reasonably estimated the soil water content profiles, particularly the status of soil water at the soil‐atmosphere interface. The mean absolute error, which describes the average absolute deviation between measured and simulated soil water contents, was 0.015 m3 m−3. The HYDROLOGY submodel of WEPS shows a potential to accurately simulate soil water dynamics, as needed for wind erosion modeling. The submodel successfully predicts the changes in water content at the soil surface, which relate to the susceptibility of the soil to wind erosion.

Evaluation of hydrologic parameters in a semiarid rangeland using remotely sensed spectral data

A study was conducted to determine the relation between remotely sensed spectral data and measurements of vegetation‐related hydrologic parameters in a semiarid rangeland in southeast Arizona. Throughout the measurement periods, ranging from June to September 1990, eight sites in the U.S. Department of Agriculture's Agricultural Research Service Walnut Gulch experimental watershed were monitored for water and energy fluxes and other meteorological and biological parameters. Corresponding spectral data were acquired with ground‐based radiometers, low‐altitude aircraft‐mounted instruments, and Landsat thematic mapper sensors. Spectral indices were derived from measurements of surface reflectance, based on their response to variations in hydrologic parameters and sensitivity to unrelated variables, such as solar zenith angle and soil differences. A soil‐adjusted vegetation index, SAVI (derived from red and NIR reflectance factors), was found to be highly correlated with the temporal changes in vegetation cover and biomass, but less successful in discriminating spatial differences in cover and biomass across the watershed. Significant relations were found between the surface‐air temperature (Ts‐Ta) difference and measurements of soil moisture content, though the shape differed from that previously published for bare soil. The relation between daily evaporation rate and measurements of (Ts‐Ta) and daily net radiation was similar to that derived previously for irrigated pasture and dryland shortgrass in France but differed from that derived for irrigated wheat. These results emphasized the strengths and limitations of the use of spectral data for estimation of hydrologic characteristics of sparsely vegetated sites and suggested a need for reevaluation of common empirical relations between remotely sensed measurements and surface characteristics for application to rangeland areas.

EVAPORATION MEASUREMENTS AND PREDICTIONS FROM SOILS UNDER CROP CANOPIES

ABSTRACT Daily evaporation rates were measured with two sizes of lysimeters: (1) mini-lysimeters, 15 cm Inside Diameter (I.D.) and 20 cm long; and (3) micro-lysimeters 7.6 cm I.D. and 6 cm long. The field studies were conducted in the semi-arid climate of west central Nebraska and the sub-humid climate of eastern Nebraska. Silt loam, fine sand, and silty clay loam soils were used in the experiment. Crop roots were excluded from the lysimeters. The micro-lysimeters were refilled daily with soil in the field plot. The following day they measured evaporation. Since the micro-lysimeters most closely matched the field soil water, their measured evaporation rates provided validation for the mini-lysimeters, which were filled with undisturbed soil once each season. Soil water contents in the mini-lysimeters were matched to the surrounding field soil after major wetting events; however, the mini-lysimeters became wetter than the surrounding soil which was subject to water extraction by crops. For sprinkler irrigated com with full canopy cover of the soil, the evaporation rates from the mini-lysimeters averaged 0.2 mm/da more than the micro-lysimeters. Evaporation rates from the mini-lysimeters were compared with predictions from the combination of two energy based models. The Ritchie (1972) model calculated the net radiation at the soil surface under a crop canopy. The Idso (1979) model took this information plus air and soil surface temperatures to predict evaporation. There wasn't any on-site calibration of the model components. Idso's model would need further calibration to cover the range of soils in this study. The low values for net radiation at the soil surface under dense shading may lead to under prediction of evaporation from these models.

Model for predicting evaporation from a row crop with incomplete cover

A model is presented for calculating the daily evaporation rate from a crop surface. It applies to a row crop canopy situation in which the soil water supply to the plant roots is not limited and the crop has not come into an advanced stage of maturation or senescence. The crop evaporation rate is calculated by adding the soil surface and plant surface components (each of these requiring daily numbers for the leaf area index), the potential evaporation, the rainfall, and the net radiation above the canopy. The evaporation from the soil surface Es is calculated in two stages: (1) the constant rate stage in which Es is limited only by the supply of energy to the surface and (2) the falling rate stage in which water movement to the evaporating sites near the surface is controlled by the hydraulic properties of the soil. The evaporation from the plant surfaces Ep is predicted by using an empirical relation based on local data, which shows how Ep is related to Eo through the leaf area index. The model was used to obtain the total evaporation rate E = Es + Ep of a developing grain sorghum (Sorghum bicolor L.) canopy in central Texas. The results agreed well with values for E measured directly with a weighing lysimeter.

Dryland Evaporative Flux in a Subhumid Climate: III. Soil Water Influence1

AbstractThis investigation was conducted to determine the relationship between evaporative rates of field‐grown cotton (Gossypium sp.) and grain sorghum [Sorghum bicolor (L.) Moench] and the soil water status for use in predicting evaporation on watersheds.Soil water content and soil water matric potential of Houston Black clay were measured throughout complete growing seasons for cotton and grain sorghum concurrently with measurements of the daily evaporation rate. Evaporation rates were independent of the soil water status until soil water was depleted beyond a threshold value. This threshold, termed the lower limit for potential evaporation (LLE0), was reached when approximately 18.2 cm of water had been removed from a soil profile initially wet. Another 6.5 cm of soil water was extracted at a decreasing rate before evaporation practically stopped. Evaporation rates after the LLE0 threshold was reached were practically independent of the energy available for evaporation and depended on the rooting distribution and the water movement to the roots. An analysis of the soil water transmission characteristics after the threshold LLE0 was reached showed that practically all the water extracted by plant roots was moving from the volume of soil immediately surrounding the roots. This result points out the need for growing crops with deep, dense root systems in dryland for maximum utilization of stored soil water.

THE ATMOSPHERIC WATER BALANCE AND THE HYDROLOGY OF LARGE RIVER BASINS1

ABSTRACTThe concept of using the atmospheric water balance technique in the study of the hydrology of large (greater than 105km2) river basins is described. The atmospheric water balance technique consists of determining the spacial and time distributions and fluxes of water vapor through the atmospheric volume overlying the basin. The quantity precipitation minus evaporation at the earth's surface is determined as a residual of the computation. A review of the results of various experiments employing this technique is provided.The incorporation of the technique in a study of the hydrology of a large river basin is demonstrated by showing the results of a study of the hydrometeorology of the Upper Colorado River Basin. The example covers the study of eleven winter seasons, November through April, 1957–1968.The seasonal accumulation of water over the basin as determined by the atmospheric water balance is highly correlated with annual runoff. Correlation coefficient r = .8. The daily evaporation rate during dry days varies by a factor of two over the winter season, and is shown to be related to the incoming solar radiation intensity.

Evaporation Rates of Capillary-Watered Tomatoes in an East-West Glasshouse

SummaryCapillary-watered beds 71 ft. long, 25 in. wide and 7 in. deep were installed at six positions across the width of the west half of a tenth-acre, east-west orientated, vinery glasshouse in order to measure the spatial variation in the daily evaporation rates of a tomato crop. Each bed was equipped with a separately metered water supply so that, assuming there was no drainage or leakage, a daily change in meter reading represented the loss by evaporation.From planting out in early March until mid-April there was little variation in daily evaporation rates across the width of the house. The variation increased as the crop grew in height and was greatest on bright sunny days and least on dull cloudy days. Maximum variation was registered on a bright sunny day in early May when the southernmost bed lost 23% more, and the northern beds from 5 to 11% less, than the mean daily evaporation rate.The extent of the variation in space and time emphasized the difficulty of determining when and how much water to apply to surface-irrigated crops and the advantage of capillary watering in supplying each plant with its precise requirement.

The heat balance of class A evaporation pan

The heat balance of a U.S. Weather Bureau class A evaporation pan located near Tucson, Arizona, was calculated for selected periods during the interval July 26–31, 1963. The method used required two pans, one of which was insulated on the side and bottom to prohibit heat transfer through these surfaces. For 10 of the 14 observation periods, heat transferred into the uninsulated pan via the side or bottom accounted for 29% of the total heat added to the pan. In the remaining periods, 6% of the heat leaving the pan was transferred through the side or bottom. Elimination of this heat transfer in the insulated pan resulted in an average daytime water temperature 2°C lower than that in the standard pan and a reduction of the daily evaporation rate by 28%. The data show the necessity of taking into account the heat transfer through the walls of the pan, especially when evaporation of natural water bodies is estimated from pan evaporation data. The heat balance method described offers one way in which the magnitude of this heat transfer can be determined. (Key words: Evaporation; lakes; meteorology; hydrology.)

Comparison of the Physical Factors of Habitats

Theoretically, the differentiation between the floras or faunas of two habitats should be an expression of the differences which obtain in their physical factors, including among such physical factors those which are due to the reactional effects of organisms on the environment. When these factors are measured, however, the variability which is found (either from place to place or from time to time) in any habitat is often so great as to be a source of despair to the ecologist who is seeking to interpret biological consequences in terms of physical causes. Most ecologists now probably realize that, because of the great variability which may be found in one and the same habitat with respect to any physical factor which may be under consideration for two or more habitats which are being compared, a few measurements in each are practically valueless as a basis for generalization concerning the nature or magnitude of the differences between them. Except in the more extreme cases, in which differences are so great as to be obvious without the making of actual measurements, trustworthy conclusions concerning differentiation in the physical conditions of two environments must depend upon the comparison of large series of simultaneous measurements. Such comparisons are essentially statistical in nature. They may in many cases be most advantageously made by methods long employed in biometric work but heretofore little used in ecological work. Let us take two or more stations in which simultaneous measurements of some environmental variable have been made for N days. The method of comparison ordinarily employed by ecologists is to plot the magnitudes of the variables in the two stations as ordinates on the axis of time throughout the period of time during which the measurements were made. Thus diagram i shows the daily evaporation rate at four stations near Bemidji, Minnesota, for the month of August, I926. Notwithstanding the enormous variability in each of the stations, the diagram shows clearly that the evaporation rate in the open burn is conspicuously higher than in any other habitat, and that there are clearly marked differences between certain other habitats. It also shows that there is a tendency for the evaporation rates in these habitats to vary together, higher