Lake Evaporation: A Model Study

Reliable evaporation data are an essential requirement in any water and/or energy budget studies. This includes operation and management of both urban and agricultural water resources. Evaporation from large, open water surfaces such as lakes and reservoirs may influence many agricultural and irrigation decisions. In this study evaporation from Bear Lake in the states of Idaho and Utah was measured using advanced research instruments (Bowen Ratio and Eddy Correlation). Actual over-lake evaporation and weather data measurements were used to understand the mechanism of evaporation in the lake, determine lake-related parameters (such as roughness lengths, heat storage, net radiation, etc.), and examine and evaluate existing lake evaporation methods. This enabled the development of a modified and flexible model incorporating the tested methods for hourly and daily best estimates of lake evaporation using nearby simple land-based weather data and, if available, remotely sensed data. Average evaporation from Bear Lake was about 2 mm/day during the summer season (March-October) of this two-year (1993-1994) study. This value reflects the large amount of energy consumed in heating the water body of the lake. Moreover, evaporation from the lake was not directly related to solar radiation. This observation was clear during nighttime when the evaporation continued with almost the same rate as daytime evaporation. This explains the vital role of heat storage in the lake as the main driving energy for evaporation during nighttime and daytime cloudy sky conditions. When comparing over-lake and nearby land-based weather parameters, land-based wind speed was the only weather parameter that had a significant difference of about 50% lower than over-lake measurements. other weather parameters were quite similar. The study showed that evaporation from the lake can be accurately estimated using Penman-type equations if related parameters such as net radiation, heat storage, and aerodynamic effect are evaluated properly to reflect conditions over the lake. Using other methods may lead to unacceptable errors

Evaporation Estimation of Rift Valley Lakes: Comparison of Models

Evapotranspiration (ET) accounts for a substantial amount of the water flux in the arid and semi-arid regions of the World. Accurate estimation of ET has been a challenge for hydrologists, mainly because of the spatiotemporal variability of the environmental and physical parameters governing the latent heat flux. In addition, most available ET models depend on intensive meteorological information for ET estimation. Such data are not available at the desired spatial and temporal scales in less developed and remote parts of the world. This limitation has necessitated the development of simple models that are less data intensive and provide ET estimates with acceptable level of accuracy. Remote sensing approach can also be applied to large areas where meteorological data are not available and field scale data collection is costly, time consuming and difficult. In areas like the Rift Valley regions of Ethiopia, the applicability of the Simple Method (Abtew Method) of lake evaporation estimation and surface energy balance approach using remote sensing was studied. The Simple Method and a remote sensing-based lake evaporation estimates were compared to the Penman, Energy balance, Pan, Radiation and Complementary Relationship Lake Evaporation (CRLE) methods applied in the region. Results indicate a good correspondence of the models outputs to that of the above methods. Comparison of the 1986 and 2000 monthly lake ET from the Landsat images to the Simple and Penman Methods show that the remote sensing and surface energy balance approach is promising for large scale applications to understand the spatial variation of the latent heat flux

Reintroducing radiometric surface temperature into the Penman-Monteith formulation

Here we demonstrate a novel method to physically integrate radiometric surface temperature (TR) into the Penman-Monteith (PM) formulation for estimating the terrestrial sensible and latent heat fluxes (H and λE) in the framework of a modified Surface Temperature Initiated Closure (STIC). It combines TR data with standard energy balance closure models for deriving a hybrid scheme that does not require parameterization of the surface (or stomatal) and aerodynamic conductances (gS and gB). STIC is formed by the simultaneous solution of four state equations and it uses TR as an additional data source for retrieving the “near surface” moisture availability (M) and the Priestley-Taylor coefficient (α). The performance of STIC is tested using high-temporal resolution TR observations collected from different international surface energy flux experiments in conjunction with corresponding net radiation (RN), ground heat flux (G), air temperature (TA), and relative humidity (RH) measurements. A comparison of the STIC outputs with the eddy covariance measurements of λE and H revealed RMSDs of 7–16% and 40–74% in half-hourly λE and H estimates. These statistics were 5–13% and 10–44% in daily λE and H. The errors and uncertainties in both surface fluxes are comparable to the models that typically use land surface parameterizations for determining the unobserved components (gS and gB) of the surface energy balance models. However, the scheme is simpler, has the capabilities for generating spatially explicit surface energy fluxes and independent of submodels for boundary layer developments

Calculation of Real Evapotranspiration by the Application of Metric Method on Landsat-8 Data

In geological remote sensing approaches for estimating evapotranspiration, METRIC method is among the most modern and precise approaches that many positive experiments have been reported regarding its applicability. In this study, the value of actual evapotranspiration (ET) occurred in Marvdasht farmlands, Fars province, Iran, was calculated instantaneously (hourly) and daily (24 hours), at 24 April 2017 using METRIC method and Lansat-8 data. In order to accuracy assessment of the results, estimated values were compared to the values calculated with Penman Monteith method in places that covers by alfafa crop. Our observations showed that ET values obtained via METRIC model on average, have 0.51mm difference in estimations, comparing to the Penman Manteith method

Estimation Of Evapotranspiration Based On Local Meteorological Data, For Penang Island

Evapotranspiration (ET) constitute a large portion of hydrological cycle which is stabilizing energy balance at the surface as a consequence of change energy flux between land surface and atmosphere. Usually, rate of evaporation obtain from Meteorological services while data of evapotranspiration is rarely available. In this study, Surface Energy Balance Systems (SEBS) has been utilized to measure turbulent flux and evaporative fraction in order to estimate rate of evapotranspiration using remotely sensed data and meteorological observation. SEBS required three datasets. First data sets is meteorology observation consist of wind speed, air pressure, relative humidity and air temperature

An Intercomparison of Satellite-Based Daily Evapotranspiration Estimates under Different Eco-Climatic Regions in South Africa

Knowledge of evapotranspiration (ET) is essential for enhancing our understanding of the hydrological cycle, as well as for managing water resources, particularly in semi-arid regions. Remote sensing offers a comprehensive means of monitoring this phenomenon at different spatial and temporal intervals. Currently, several satellite methods exist and are used to assess ET at various spatial and temporal resolutions with various degrees of accuracy and precision. This research investigated the performance of three satellite-based ET algorithms and two global products, namely land surface temperature/vegetation index (TsVI), Penman–Monteith (PM), and the Meteosat Second Generation ET (MET) and the Global Land-surface Evaporation: the Amsterdam Methodology (GLEAM) global products, in two eco-regions of South Africa. Daily ET derived from the eddy covariance system from Skukuza, a sub-tropical, savanna biome, and large aperture boundary layer scintillometer system in Elandsberg, a Mediterranean, fynbos biome, during the dry and wet seasons, were used to evaluate the models. Low coefficients of determination (R2) of between 0 and 0.45 were recorded on both sites, during both seasons. Although PM performed best during periods of high ET at both sites, results show it was outperformed by other models during low ET times. TsVI and MET were similarly accurate in the dry season in Skukuza, as GLEAM was the most accurate in Elandsberg during the wet season. The conclusion is that none of the models performed well, as shown by low R2 and high errors in all the models. In essence, our results conclude that further investigation of the PM model is possible to improve its estimation of low ET measurements

Closure in Surface Flux Estimation by Energy Balance Model: Comparison of Priestly-Taylor and Penman-Monteith Computations for a Tropical Site in Ibadan

Increasing demand to further understand complexity in surface energy flux partitioning necessitates the adaptation of numerous estimation methods to fit the site of observation. This is useful for reducing the uncertainty in physically measurable parameters especially those in tropical regions with high human interference in the atmospheric boundary layer. In this study, we used computations from two methods - the Priestley-Taylor (PT) and the Penman-Monteith (PM), based on the Energy Balance model to ascertain closure performance in the surface flux estimations. The study was carried out at the Nigerian Meteorological Experiment III site (7.38oN and 3.93oE, 224.2m) located in Ibadan, Southwest Nigeria. Thirty days of a year (2006) dataset were examined using the Bowen ratio (BR) energy balance model to validate the PT and PM methods. The systems were examined across daily and diurnal cycles to better understand the differences in energy partitioning. Results showed that both systems generally favored latent heat flux compared to sensible heat flux perhaps due to above-normal rainfall during the period. The PM method performed better than the PT method with a period average for the sensible heat and latent heat fluxes as 32.05 Wm-2 and 67.66 Wm-2 respectively, accounting for 29.22% and 61.39% of the total net radiation. The PT method underestimates the sensible heat flux by as much as 19.70 Wm-2 compared to the PM method, with a period average of 12.36 Wm-2 representing 11.26% of total net radiation. The PM method also gives a period average Bowen ratio estimate of 0.55, consistent with the standard range for grasslands. The study suggests that the performance of the PM method is related to its response to heat and water vapor transfer over humid regions and would contribute to further research on land-surface interactions over the tropics. Finally, we propose that the measurement of available energy, net radiation, and ground heat flux should be separated for different collocated systems in order to reduce the forcing of closure and aid in proper partitioning of the fluxes. Keywords: surface energy flux, energy balance model, Priestly-Taylor, Penman-Monteith, West Africa, latent heat, sensible heat, NIMEX_3 DOI: 10.7176/JEES/11-5-05 Publication date:May 31st 202