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1 
The influence of the diurnal variation of stability on potential evaporationEk, Michael Bryan 10 December 1982 (has links)
A method of calculating surface evapotranspiration by separately
including the effects of vegetation and atmospheric evaporative demand
under the condition of nonlimiting soil moisture is presented. A
literature survey is conducted to determine the effects of plants on
evapotranspiration.
To represent the atmospheric evaporative demand, the original
potential evaporation equation of Penman (1948) is utilized and then
modified to include the effect of atmospheric stability using turbulent
exchange coefficients formulated by Louis et al. (1982). The
original and modified Penman expressions are compared for different
asymptotic cases. Using boundary layer data from the Wangara experiment
(Clarke et al., 1971), the diurnal variations of the original
and modified Penman equations are compared. The daily total potential
evaporation using linearized and integrated forms of the original and
modified expressions are also compared. Finally, the nonlinear effects
of averaging both the original and modified expressions are
examined. It is found that including the diurnal variations of stability
in the modified expression causes large hourly differences with
the original expression under nonneutral conditions, while daily
averages of the two compared fairly well. The diurnal variation of
the surface moisture flux appears to be much larger than predicted
by the original Penman expression. However, the original Penman expression
remains a reasonable estimate of the 24hour total potential
evaporation. / Graduation date: 1983

2 
PenmanMonteith surface resistance for hybrid poplar treesButler, Dana Anthony 21 April 2000 (has links)
The application of the widely used PenrnanMonteith evapotranspiration
equation to hybrid poplar trees is impossible without a valid surface resistance.
The increase in applications of dripirrigated hybrid poplar trees for wood chip
stock and veneer production, as well as bioremediation, constitutes a need for
estimating the evapotranspiration of these trees. To the author's knowledge, there
are no published estimates of surface resistance for poplar trees.
Six years of weekly soil moisture content for dripirrigated, hybrid poplar
trees were used in a water balance to compute evapotranspiration. The weekly data
were adjusted with reference evapotranspiration data to compute a daily
evapotranspiration. Only data that represent fully leaved hybrid poplars are used in
this study and the data were screened for the effects of drainage. Additional
parameters applied in this study include solar radiation, temperature, wind speed
and relative humidity taken at a nearby AGRIMET Weather Station.
The results of this study indicate that surface resistance values cannot be
described as a function of meteorological data within the constraints of the current
experiment design. The graph of poplar evapotranspiration versus surface
resistance shows that for a given evapotranspiration there can be multiple rs values.
This scatter is the influence of parameters other than rs within the PenmanMonteith
model. The use of an instrument to directly measure the surface
resistance is recommended in further studies. / Graduation date: 2000

3 
An experimental investigation of the evaporation rate from stationary water pools into moving airFarley, Beth Ann 12 1900 (has links)
No description available.

4 
Evaluation and verification of conservation and similarity approaches for estimating regional evapotranspirationDavis, Luke Howell 08 1900 (has links)
No description available.

5 
Estimating bank storage and evapotranspiration using soil physical and hydrological techniques in a gaining reach of the San Pedro River, ArizonaWhitaker, Martha Patricia Lee. January 2000 (has links)
Bank storage is defined as a volume of water that periodically infiltrates a river's banks during increases in stream stage. It is a potentially critical variable for accurately modeling the water budget in semiarid riparian systems, but is particularly difficult to assess and quantify. It is especially essential for understanding groundwater/surfacewater interactions. In collaboration with other projects, a fieldscale vadose monitoring effort took place in the San Pedro Riparian National Conservation Area (SPRNCA), Arizona. The San Pedro River flows north from Mexico into the United States, and SPRNCA is a 60 km stretch of U.S.protected ecosystem north of the border. In addition to a progressive climate of ecological conservation, hydrological research that leads to an improved understanding of the water budget will ultimately improve the prospects for improved water policy decisions. Soil moisture, stream stage, and soil tension data were collected for over 8 consecutive months in both 1997 and 1998, and the data were used as input into a software program called HYDRUS2D (§imiinek et al. 1996), which models twodimensional, variably saturated flow. Fieldcollected data and subsequent modeling efforts suggest that the effects of bank storage were estimated to contribute approximately 8.5% of the river's total flow for 147 days in 1997. Accordingly, bank storage and its effects should be considered in future waterbalance simulations of streamaquifer interaction, and of the San Pedro River in particular. In addition, model estimates of root water uptake match favorably with other estimates of evapotranspiration in the cottonwoodwillow forest gallery of the SPRNCA.

6 
Suburban evapotranspiration estimates in Vancouver from energy balance measurementsKalanda, Brian Douglas January 1979 (has links)
This study is concerned with the energy balance of a suburban area of south central Vancouver and in particular with the role of evapotranspiration in this balance. In the late summer  early fall of 1977 a measurement program was conducted to determine the energy balance components using the Bowen ratio  energy balance approach. The Bowen ratio was obtained from differential psychrometric measurements taken above mean rooflevel. Net radiation was measured directly and the volumetric heat storage was parameterized in terms of net radiation.
The results indicate that the Bowen ratio  energy balance approach is applicable to suburban environments. An error analysis developed for the reversing psychrometer system indicates that the errors in the turbulent fluxes were typically 10  20%. The turbulent latent heat flux was always a significant and often the dominant energy sink for this 'surface'. This is shown to be largely due to soil moisture replenishment by precipitation and irrigation (especially lawn sprinkling). The turbulent fluxes tended to be inphase with net radiation during the day. This appears to be a result of the decreasing importance of nonradiative controls (especially the vapour pressure deficit) on evapotranspiration as the land use changes from rural to heavily urbanized. Sustained periods of positive turbulent fluxes were recorded at night, however the Bowen ratio was predominantly negative indicating that only one turbulent flux was positive. The data do not reveal any dependence on wind direction. The influence (if any) of the
sea breeze could not be isolated. The equilibrium evapotranspiration rate often closely approximated the measured evapotranspiration. / Arts, Faculty of / Geography, Department of / Graduate

7 
A comparative evaluation of residual energy balance, Penman, and PenmanMonteith estimates of daytime variation of evapotranspirationOrtegaFarias, Samuel Orlando 28 September 1993 (has links)
Graduation date: 1994

8 
Sensible heat flux and evaporation for sparse vegetation using temperaturevariance and a dualsource model.Abraha, Michael Ghebrekristos. January 2010 (has links)
The high population growth rate and rapid urbanization that the world is experiencing today has aggravated the competition for the already scarce resource ¡V water ¡V between the agricultural sector and the other economic sectors. Moreover, within the agricultural sector, water is increasingly being used for commercial plantations as opposed to growing food crops, threatening food security. Therefore, it is very important that this scarce resource is managed in an efficient and sustainable manner, for now and future use. This requires understanding the process of evaporation for accurate determination of wateruse from agricultural lands. In the past, direct measurements of evaporation have proven difficult because of the cost and complexity of the available equipments, and level of expertise involved. This justifies a quest for relatively simple, accurate and inexpensive methods of determining evaporation for routine field applications. Estimation of sensible heat flux (H) from high frequency air temperature measurements and then calculating latent energy flux (ƒÜE) and hence evaporation as a residual of the shortened surface energy balance equation, assuming that closure is met, is appealing in this sense. Concurrent net irradiance (Rn) and soil heat flux (G) measurements can be conducted with relative ease for use in the energy balance equation. Alternately, evaporation can also be mathematically modelled, using single or multilayer models depending on vegetation cover, from less expensive routine meteorological observations. Therefore, the ultimate objective of this study is to estimate and model H and ƒÜE, and thereby evaporation, accurately over sparsely vegetated agricultural lands at low cost and effort. Temperaturevariance (TV) and surface renewal (SR) methods, which use highfrequency (typically 2 to 10 Hz) air temperature measurements, are employed for estimation of H. The TV method is based on the Monin and Obukhov Similarity Theory (MOST) and uses statistical measures of the high frequency air temperature to estimate H, including adjustments for stability. The SR method is based on the principle that an air parcel near the surface is renewed by an air parcel from above and, to determine H, it uses higher order air temperature differences between two consecutive sample measurements lagged by a certain time interval. Single and doublelayer models that are based on energy and resistance combination theory were also used to estimate evaporation and H from sparse vegetation. Single and doublelayer models that were extended to include inputs of radiometric temperature in order to estimate H were also used. The transmission of solar irradiance to the soil beneath in sparse canopies is variable and depends on the vegetation density, cover and apparent position of the sun. A threedimensional radiation interception model was developed to estimate this transmission of solar irradiance and was used as a submodule in the doublelayer models. Estimations of H from the TV (HTV), SR (HSR) and doublelayer models were compared against H obtained from eddy covariance (HEC), and the modelled ƒÜE (single and doublelayer) were compared with that obtained from the shortened energy balance involving HEC. Besides, longterm ƒÜE calculated from the shortened energy balance using HTV and HSR were compared with those calculated using HEC. Unshielded and naturallyventilated finewire chromelconstantan thermocouples (TCs), 75 ƒÝm in diameter, at different heights above the ground over sparse Jatropha curcas trees, mixed grassland community and bare fallow land were used to measure air temperature. A threedimensional sonic anemometer mounted at a certain height above the ground surface was also used to measure virtual temperature and wind speed at all three sites. All measurements were done differentially at 10Hz frequency. Additional measurements of Rn, G and soil water content (upper 60 mm) were also made. The Jatropha trees were planted in a 3m plant and interrow spacing in a 50 m ¡Ñ 60 m plot with the surrounding plots planted to a mixture of Jatropha trees and Kikuyu grass. Average tree height and leaf area index measurements were taken on monthly and bimonthly basis respectively. An automatic weather station about 10 m away from the edge of the Jatropha plot was also used to obtain solar irradiance, air temperature and relative humidity, wind speed and direction and precipitation data. Soil water content was measured to a depth of 1000 mm from the surface at 200 mm intervals. Soil and foliage surface temperatures were measured using two nadirlooking infrared thermometers with one mounted directly above bare soil and the other above the trees. The threedimensional solar irradiance interception model was validated using measurements conducted on different trees and planting patterns. Solar irradiance above and below tree canopies was measured using LI200 pyranometer and tube solarimeters respectively. Leaf area density (LAD) was estimated from LAI, canopy shape and volume measurements. It was also determined by scanning leaves using either destructive sampling or tracing method. The performance of the TV method over sparse vegetation of J. curcas, mixed grassland community and fallow land was evaluated against HEC. Atmospheric stability conditions were identified using (i) sensor height (z) and Obukhov length (L) obtained from EC and (ii) air temperature difference between two thermocouple measurement heights. The HTV estimations, adjusted and not adjusted for skewness (actual and estimated) of air temperature (sk), for unstable conditions only and for all stability conditions were used. An improved agreement in terms of slope, coefficient of determination (r2) and root mean square error (RMSE), almost over all surfaces, was obtained when the temperature difference rather than the z/L means of identifying stability conditions was used. The agreement between the HTV and HEC was improved for estimations adjusted for actual sk than not adjusted for sk. Improved agreement was also noted when HTV was adjusted using estimated sk compared to not adjusting for sk over J. curcas. The TV method could be used to estimate H for surfaces with varying homogeneity with reasonable accuracy. Longterm wateruse of a fetchlimited sparse vegetation of J. curcas was determined as a residual of the shortened surface energy balance involving HTV and HSR and compared with those estimated using HEC. Concurrent measurements of Rn and G were also performed. The longterm wateruse of J. curcas trees calculated from the shortened surface energy balance involving HTV and HSR agreed very well when compared with those obtained from HEC. The seasonal HTV and HSR also agreed very well when compared with HEC. Changes in structure of the canopy and environmental conditions appeared to influence partitioning of the available energy into H and ƒÜE. The seasonal total evaporation for the EC, TV and SR methods amounted to 626, 640 and 674 mm respectively with a total rainfall of 690 mm. Footprint analysis also revealed that greater than 80% of the measured flux during the day originates from within the surface of interest. The TV and SR methods, therefore, offer a relatively lowcost means for longterm estimation of H, and ƒÜE, hence the total evaporation, using the shortened surface energy balance along with measurements of Rn and G. Evaporation and biomass production estimations from tree crops requires accurate representation of solar irradiance transmission through the canopy. A relatively simple threedimensional, hourly timestep treecanopy radiation interception model was developed and validated using measurements conducted on isolated trees, hedgerows and tree canopies arranged in tramline mode. Measurements were obtained using tube solarimeters placed 0.5 m from each other starting from the base of a tree trunk in four directions, along and perpendicular to the row up to midway between trees and rows. Modelsimulations of hourly radiant transmittance were in good agreement with measurements with an overall r2 of 0.91; Willmott.s index of agreement of 0.96; and general absolute standard deviation of 17.66%. Agreement between modelestimations and measurements, however, was influenced by distance and direction of the node from the tree trunk, sky conditions, symmetry of the canopy, and uniformity of the stand and leaf distribution of the canopy. The model could be useful in planning and management applications for a wide range of tree crops. PenmanMonteith (PM) equation and the Shuttleworth and Wallace (SW) model, representing single and dualsource models respectively, were used to determine the total evaporation over a sparse vegetation of J. curcas from routine automatic weather station observations, resistance parameters and vegetation indices. The threedimensional solar irradiance interception model was used as a submodule in the SW model. The total evaporation from the sparse vegetation was also determined as a residual of the shortened surface energy balance using measurements of Rn, G and HEC. The PM equation failed to reproduce the .measured. daily total evaporation during periods of low LAI, with improved agreement with increased LAI. The SW model, however, produced total evaporation estimates that agreed very well with the .measured. with a slope of 0.96, r2 of 0.91 and RMSE of 0.45 mm for a LAI ranging from 0 (no leaves) to 1.83 m2 m2. The SW model also estimated soil evaporation and plant transpiration separately, and about 66 % of the cumulative evaporation was attributed to soil evaporation. These findings suggest that the PM equation should be replaced by the SW model for surfaces that assume a range of LAI values during the growing season. The H was estimated using (i) SW model that was further developed to include surface radiometric temperature measurements; (ii) onelayer model, but linked with a twolayer model for estimation of excess resistance, that uses surface radiometric temperature; and (iii) the SW model (unmodified). The agreement between modelled and measured H, using 10min data, was in general reasonably good with RMSE (W m2) of 45.11, 43.77 and 39.86 for the three models respectively. The comparative results that were achieved from (iii) were not translated into the daily data as all models appeared to have a tendency to underestimate H. The resulting RMSEs for the daily H data for the three models were (MJ m2) 1.16, 1.17 and 1.18 respectively. It appears that similar or better agreement between measured and estimated H can be forged without the need for surface radiometric temperature measurements. The study showed, in general, that high frequency air temperature measurements can be used to estimate H with reasonable accuracy using the simple and relatively lowcost TV and SR methods. Moreover, these methods can be used to calculate ƒÜE, hence ET, as a residual of the shortened surface energy balance equation along with measurements of Rn and G assuming that energy balance closure is met. The simple and lowcost nature of these methods makes replication of measurements easier and their robust nature allows longterm measurements of energy fluxes. The study also showed that H and ƒÜE can be modeled using energy and resistance combination equations with reasonable accuracy. It also reiterated that the SWtype models, which treat the plant canopy and soil components separately, are more appropriate for estimation of H and ƒÜE over sparse vegetation as opposed to the PMtype models. / Thesis (Ph.D.)University of KwaZuluNatal, Pietermaritzburg, 2010.

9 
Sensible heat flux under unstable conditions for sugarcane using temperature variance and surface renewal.Nile, Eltayeb Sulieman. January 2010 (has links)
Increased pressure on the available limited water resources for agricultural production has a significant impact on sugarcane production. Routine monitoring of evaporation with reliable accuracy is essential for irrigation scheduling, for more efficient use of the available water resources and for management purposes. An indirect method for estimating evaporation involves measuring the sensible heat flux (H) from which latent energy flux and hence total evaporation can be calculated, as a residual using the shortened energy balance from measurements of net irradiance and soil heat flux. Various methods for measuring H may include Bowen ratio energy balance, eddy covariance (EC), flux variance (FV), optical scintillation, surface renewal (SR) and temperature variance (TV). Each method has its own advantages and disadvantages, in terms of method theoretical assumptions, accuracy, complexity, cost, fetch requirements and power consumption. The TV and SR methods are inexpensive and reasonably simple with a reduced power requirement compared to other methods since they require high frequency air temperature data which is obtained by using an unshielded naturallyventilated typeE finewire thermocouple at a single point above the canopy surface. The TV method is based on the MoninObukhov similarity theory (MOST) and uses the mean and standard deviation of the air temperature for each averaging period. Currently, there are two TV methods used for estimating sensible heat flux (HTV) at subhourly time intervals, one includes adjustment for stability, and a second that includes adjustment for air temperature skewness. Another method used to estimate sensible heat flux from the mean and standard deviation of air temperature is based on MOST and uses spatial secondorder air temperature structure function. For the TV method adjusted for stability and the method based on MOST that uses a spatial secondorder air temperature structure function, the MoninObukhov atmospheric stability parameter () is needed. The parameter can be estimated from EC measurements or alternatively estimated independently using an iteration process using horizontal wind speed measurements. The TV method including adjustment for air temperature skewness requires the mean and standard deviation of the air temperature and air temperature skewness for each averaging time period as the only input. The SR method is based on the coherent structure concept. Currently, there are various SR models method for estimating sensible heat flux. These include an ideal SR analysis model method based on an air temperature structure function analysis, the SR analysis model with a finite microfront period, combined SR with Ktheory and combined SR model method based on MOST. The ideal SR analysis model based on an air temperature structure function analysis should be calibrated to determine the SR weighting factor (). The other SR approaches require additional measurements such as crop height and horizontal wind speed measurements. In all of the SR approaches, air temperature time lags are used when calculating the air temperature structure functions. In this study, the performance of TV and SR methods were evaluated for estimation of sensible heat and latent energy fluxes at different heights for air temperature time lags of 0.4 and 0.8 s for daytime unstable conditions against EC above a sugarcane canopy at the Baynesfield Estate in KwaZuluNatal, South Africa. For all methods, latent energy flux (LE) and hence evaporation was estimated as a residual from the shortened energy balance equation using H estimates and net irradiance and soil heat flux density measurements. The ideal SR analysis model method based on an air temperature structure function analysis approach was calibrated and validated against the EC method above the sugarcane canopy using nonoverlapping data sets for daytime unstable conditions during 2008. During the calibration period, the SR weighting factor was determined for each height and air temperature time lag. The magnitude of ranged from 0.66 to 0.55 for all measurement heights and an air temperature time lag of 0.8 s. The value increased with a decrease in measurement height and an increase in air temperature time lag. For the validation data set, the SR sensible heat flux (HSR) estimates corresponded well with EC sensible heat flux (HEC) for all heights and both air temperature time lags. The agreement between HSR and HEC improved with a decrease in measurement height for the air temperature time lag of 0.8 s. The best HSR vs HEC comparisons were obtained at a height of 0.20 m above the crop canopy using = 0.66 for an air temperature time lag of 0.8 s. The residual estimates of latent energy flux by SR and EC methods were in good agreement. The LESR at a height of 0.20 m above the canopy yielded the best comparisons with LEEC estimated as a residual. The performance of the TV method, including adjustment for stability, and / Thesis (Ph.D.)University of KwaZuluNatal, Pietermaritzburg, 2010.

10 
Heat and energy exchange above different surfaces using surface renewal.Mengistu, Michael Ghebrekidan. January 2008 (has links)
The demand for the world’s increasingly scarce water supply is rising rapidly, challenging its availability for agriculture and other environmental uses, especially in water scarce countries, such as South Africa, with mean annual rainfall is well below the world’s average. The implementation of effective and sustainable water resources management strategies is then imperative, to meet these increasingly growing demands for water. Accurate assessment of evaporation is therefore crucial in agriculture and water resources management. Evaporation may be estimated using different micrometeorological methods, such as eddy covariance (EC), Bowen ratio energy balance (BR), surface renewal (SR), flux variance (FV), and surface layer scintillometry (SLS) methods. Despite the availability of different methods for estimating evaporation, each method has advantages and disadvantages, in terms of accuracy, simplicity, spatial representation, robustness, fetch, and cost. Invoking the shortened surface energy balance equation for which advection and stored canopy heat fluxes are neglected, the measurement of net irradiance, soil heat flux, and sensible heat flux allows the latent energy flux and hence the total evaporation amount to be estimated. The SR method for estimating sensible heat, latent energy, and other scalars has the advantage over other micrometeorological methods since it requires only measurement of the scalar of interest at one point. The SR analysis for estimating sensible heat flux from canopies involves high frequency air temperature measurements (typically 2 to 10 Hz) using 25 to 75 ìm diameter finewire thermocouples. The SR method is based on the idea that parcel of air near a surface is renewed by an air parcel from above. The SR method uses the square, cube, and fifth order of two consecutive air temperature differences from different time lags to determine sensible heat flux. Currently, there are three SR analysis approaches: an ideal SR analysis model based on structure function analysis; an SR analysis model with finite microfront period; and an empirical SR analysis model based on similarity theory. The SR method based on structure function analysis must be calibrated against another standard method, such as the eddy covariance method to determine a weighting factor á which accounts for unequal heating of air parcels below the air temperature sensor height. The SR analysis model based on the finite microfront time and the empirical SR analysis model based on similarity theory need the additional measurement of wind speed to estimate friction velocity. The weighting factor á depends on measurement height, canopy structure, thermocouple size, and the structure function air temperature lag. For this study, á for various canopy surfaces is determined by plotting the SR sensible heat flux SR H against eddy covariance EC H estimates with a linear fit forced through the origin. This study presents the use of the SR method, previously untested in South Africa, to estimate sensible heat flux density over a variety of surfaces: grassland; Triffid weed (Chromolaena odorata); Outeniqua Yellow wood (Podocarpus Falcatus) forest; heterogeneous surface (Jatropha curcas); and open water surface. The sensible heat flux estimates from the SR method are compared with measurements of sensible heat flux obtained using eddy covariance, Bowen ratio, flux variance, and surface layer scintillometer methods, to investigate the accuracy of the estimates. For all methods used except the Bowen ratio method, evaporation is estimated as a residual using the shortened energy balance from the measured sensible heat and from the additional measurements of net irradiance and soil heat flux density. Sensible heat flux SR H estimated using the SR analysis method based on air temperature structure functions at a height of 0.5 m above a grass canopy with a time lag r = 0.5 s, and á =1 showed very good agreement with the eddy covariance EC H , surface layer scintillometer SLS H , and Bowen ratio BR H estimates. The halfhourly latent energy flux estimates obtained using the SR method SR ë E at 0.5 m above the grass canopy for a time lag r = 0.5 s also showed very good agreement with EC ë E and SLS ë E . The 20minute averages of SR ë E compared well with Bowen ratio BR ë E estimates. Sensible heat and latent energy fluxes over an alien invasive plant, Triffid weed (C. odorata) were estimated using SR , EC , FV and SLS methods. The performance of the three SR analysis approaches were evaluated for unstable conditions using four time lags r = 0.1, 0.4, 0.5, and 1.0 s. The best results were obtained using the empirical SR method with regression slopes of 0.89 and root mean square error (RMSE) values less than 30 W m2 at measurement height z = 2.85 and 3.60 m above the soil surface for time lag r = 1.0 s. Halfhourly SR H estimates using r = 1.0 s showed very good agreement with the FV and SLS estimates. The SR latent energy flux, estimated as a residual of the energy balance ë ESR , using time lag r = 1.0 s provided good estimates of EC ë E , FV ë E , and SLS ë E for z = 2.85 and 3.60 m. The performance of the three SR analysis approaches for estimating sensible heat flux above an Outeniqua Yellow wood stand, were evaluated for stable and unstable conditions. Under stable conditions, the SR analysis approach using the microfront time produced more accurate estimates of SR H than the other two SR analysis approaches. For unstable conditions, the SR analysis approach based on structure functions, corrected for á using EC comparisons produced superior estimates of SR H . An average value of 0.60 is found for á for this study for measurements made in the roughness sublayer. The SR latent energy flux density estimates SR ë E using SR H based on structure function analysis gave very good estimates compared with eddy covariance ( EC ë E ) estimates, with slopes near 1.0 and RMSE values in the range of 30 W m2. The SR ë E estimates computed using the SR analysis approach using the microfront time also gave good estimates comparable to EC ë E . The SR and EC methods were used to estimate longterm sensible heat and latent energy flux over a fetchlimited heterogeneous surface (J. curcas). The results show that it is possible to estimate longterm sensible heat and latent energy fluxes using the SR and EC methods over J. curcas. Continuous measurements of canopy height and leaf area index measurements are needed to determine á . The weighting factor á was approximately 1 for placement heights between 0.2 and 0.6 m above the Jatropha tree canopy. The daily sensible heat and latent energy flux estimates using the SR analysis gave excellent estimates of daily EC sensible heat and latent energy fluxes. Measurements of sensible heat and estimates of the latent energy fluxes were made for a small reservoir, using the SR and EC methods. The SR sensible heat flux SR H estimates were evaluated using two air temperature time lags r = 0.4 and 0.8 s at 1.0, 1.3, 1.9, 2.5 m above the water surface. An average á value of 0.175 for time lag r = 0.4 s and 0.188 for r = 0.8 s was obtained. The SR H and EC H estimates were small (40 to 40 W m2). The heat stored in water was larger in magnitude (200 to 200 W m2) compared to the sensible heat flux. The SR and EC latent energy fluxes were almost the same in magnitude as the available energy, due to the small values of the sensible heat fluxes. The daily evaporation rate ranged between 2.0 and 3.5 mm during the measurement period. The SR method can be used for routine estimation of sensible heat and latent energy fluxes with a reliable accuracy, over a variety of surfaces: short canopies, tall canopies, heterogeneous surface, and open water surface, if the weighting factor á is determined. Alternatively, the SR method can be used to estimate sensible heat flux which is exempt from calibration using the other two SR analysis approaches, with additional measurement of wind speed for estimating friction velocity iteratively. The advantages of the SR method over other micrometeorological methods are the relatively low cost, easy installation and maintenance, relatively low cost for replicate measurements. These investigations may pave the way for the creation of evaporation stations from which realtime and subhourly estimates of total evaporation may be obtained relatively inexpensively. / Thesis (Ph.D.)University of KwaZuluNatal, Pietermaritzburg, 2008.

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