Estimates Of Lake Evaporation Research Articles

Hydrological Modeling of the Cambamba Watershed in Angola Using the HEC-HMS Model

When evaluating the impact of climate change on water resources in river basins it is crucial to accurately estimate the availability of water and such can be attained through hydrological modeling of the basin. The studies of the Hydrological Modeling System (HEC-HMS) for the Cambamba River Basin in Angola has been calibrated and validated for the prediction of its hydrologic response. Due to the complexity of Hydrologic models, a good calibration of the model should be established, therefore, improving its skills and effectiveness. A combination of both the energy budget and a physically-based rainfall-runoff model, which are used for the estimation of lake evaporation, were applied in the lake water balance model. Soil storage, as well as groundwater storage coefficient, are essential parameters for estimating the simulated streamflow. For an adequate performance evaluation of the model which entails the simulation of the streamflow on Cambamba watershed and quantification of water availability, The Nash-Sutcliffe model efficiency criterion; root mean square error; percentage error in volume PEV; and percentage error in peak PEP, were implemented. Model performance is improved by using semiannual parameter sets that consider the change in hydrological conditions, as evaluated in this study. Key words: HEC-HMS, watershed, rainfall-runoff, flood hazards

A Comparison of the Diurnal Variation in Lake Surface Temperature for the Five Major Lakes of the Savannah River Basin

Satellite measurements of lake surface temperature can benefit several environmental applications such as estimation of lake evaporation, predictions of lake overturning, and meteorological forecasts. Using a one-dimensional lake simulation that incorporates satellite measurements of lake surface temperature, the average diurnal variation in lake surface temperature was obtained. The satellite measurements were obtained from the MODIS instrument aboard the Aqua and Terra satellites. Herein the functional form for the diurnal variation in surface temperature is presented for each of the five major lakes in the Savannah River Basin, which are located in South Carolina and Georgia: Lakes Jocassee, Keowee, Hartwell, Russell, and Thurmond. Differences in the diurnal variation in surface temperature between each of these lakes are identified and potential explanations for these differences are presented.

Evaluation of ten methods for estimating evaporation in a small high-elevation lake on the Tibetan Plateau

To quantify lake evaporation and its variations in time, ten methods for estimating evaporation at a temporal resolution of 10 days over a small high-elevation lake in the Nam Co lake basin of the Tibetan Plateau (TP) were evaluated by using eddy covariance (EC) observation-based reference datasets. After examination of the consistency of the parameters used in the different methods, the ranking of the methods under different conditions are shown to be inconsistent. The Bowen ratios derived from meteorological data and EC observations are consistent, and it supports a ranking of energy-budget-based methods (including the Bowen ratio energy budget, Penman, Priestley-Taylor, Brutsaert-Stricker and DeBruin-Keijman methods) as the best when heat storage in the water can be estimated accurately. The elevation-dependent psychometric constant can explain the differences between the Priestley-Taylor and DeBruin-Keijman methods. The Dalton-type methods (Dalton and Ryan-Harleman methods) and radiation-based method (Jensen-Haise) all improve significantly after parameter optimization, with better performance by the former than the latter. The deBruin method yields the largest error due to the poor relationship between evaporation and the drying power of the air. The good performance of the Makkink method, with no significant differences before and after optimization, indicates the importance of solar radiation and air temperature in estimation of lake evaporation. The Makkink method was used for long-term evaporation estimation due to lack of water temperature observations in lakes on the TP. Lastly, long-term evaporation during the open-water period (April 6 to November 15 from 1979 to 2015) were obtained; the mean bias was only 6%. A decreasing-increasing trend in lake evaporation with a turning point in 2004 was noted, and this trend corresponds to the published decreasing-increasing trend in reference evapotranspiration on the Tibetan Plateau and can be explained by variations in related meteorological variables.

Simulation of Pan Evaporation and Application to Estimate the Evaporation of Juyan Lake, Northwest China under a Hyper-Arid Climate

Because of its nature, lake evaporation (EL) is rarely measured directly. The most common method used is to apply a pan coefficient (Kp) to the measured pan evaporation (Ep). To reconstruct the long sequence dataset of Ep, this study firstly determined the conversion coefficients of Ep of two pans (φ20 and E601, each applied to a different range of years) measured synchronously at the nearest meteorological station during the unfrozen period through 1986 to 2001, and then Ep was estimated by the PenPan model that developed to the Class A pan and applied to quantify the EL of the Juyan Lake, located in the hyper-arid area of northwest China. There was a significantly linear relationship between the E601 and φ20 with the conversion coefficients of 0.60 and 0.61 at daily and monthly time scales, respectively. The annual Ep based on monthly conversion coefficients was estimated at 2240.5 mm and decreased by 6.5 mm per year, which was consistent with the declining wind speed (U) during the 60 years from 1957 to 2016. The Ep simulated by the PenPan model with the modified net radiation (Rn) had better performance (compared to Ep measured by E601) than the original PenPan model, which may be attributed to the overestimated Rn under the surface of E601 that was embedded in the soil rather than above the ground similar to the Class A and φ20. The measured monthly EL and Ep has a significantly linear relationship during the unfrozen period in 2014 and 2015, but the ratio of Ep to EL, i.e., Kp varied within the year, with an average of 0.79, and was logarithmically associated with U. The yearly mean EL with full lake area from 2005 to 2015 was 1638.5 mm and 1385.6 mm, calculated by the water budget and the PenPan model with the modified Rn, respectively; the latter was comparable to the surface runoff with an average of 1462.9 mm. In conclusion, the PenPan model with the modified Rn has good performance in simulating Ep of the E601, and by applying varied Kp to the model we can improve the estimates of lake evaporation.

Attributes of Lake Okanagan evaporation and development of a mass transfer model for water management purposes

Understanding the water budget of the valley lakes in the water-stressed Okanagan region of British Columbia is important for allocating resources to maximize social well-being, environmental quality and the economy. However, high uncertainty in existing estimates of lake evaporation prevents sound water resource decision making. To address this uncertainty, buoy- and shore-based eddy covariance and meteorological instrumentation were deployed on the largest of the valley lakes, Lake Okanagan, for approximately 3 years. The objectives were to address the uncertainty in existing Lake Okanagan evaporation estimates by describing seasonal cycles and annual rates and the meteorological attributes controlling evaporation, and developing an accurate and useful model suitable for water managers and policy makers. Results indicate that two sites on Lake Okanagan experienced average annual evaporation of 725 and 835 mm over the study period. The difference can be attributed to spatial differences in surface water temperatures, vapour pressure gradients and atmospheric stability across the lake. Good relationships were found between evaporation rates measured with the eddy covariance systems and meteorological conditions at the offshore buoys, specifically between wind speed and the surface–atmospheric vapour pressure differences. From these relationships, a mass transfer model was developed. Accounting for the seasonal cycle in atmospheric stability increased the accuracy of monthly and annual evaporation estimates from this mass transfer model, but it remains inappropriate to predict daily or hourly evaporation. The study period included years that were climatically typical, so the evaporation observations could represent values close to the long-term mean, but this is unknown. The findings of this study highlight that long-term observations of the atmosphere consistently conditioned to the lake surface are needed for water managers and decision makers to have sound data and information on lake evaporation.

Surface Meteorological Observations over Lake Malawi/Nyasa

Over-lake surface meteorology is essential for the estimation of lake evaporation and for the forcing of lake water quality and circulation models. A roving meteorological station was mounted aboard the research vessel, R/V Usipa, on Lake Malawi/Nyasa. Ship velocity and position were recorded, thus permitting winds to be corrected aboard the moving platform. This type of data is particularly sparse for tropical lakes. Of the eight full-lake cruises over the period from February, 1997 to May 1999, four yielded usable data comprising 3,316 30-min averages but restricted mainly to the wet season. In addition to winds, air temperatures, relative humidities, and water temperatures were recorded. Similar parameters were measured concurrently at up to four fixed locations on the shoreline providing a basis for comparison. An examination of the longest running series of winds and air temperatures showed no obvious interannual differences in wind speed and air temperature. Based on wind spectra, winds were divided into a diurnal component and a longer term smoothed component by digital filtering. Analysis of the shipboard winds shows an unexpectedly strong diurnal wind field in the open lake which appears to be dominated by the diurnal atmospheric circulation along the eastern shoreline. This effect is likely due to the interaction between southeast trade winds and the diurnal wind field. The long-term smoothed winds vary along the longitudinal axis of the lake, being weakest at the extremities and strongest in the middle. Calculations of an average evaporation rate based on observed meteorological data from all temporal scales using three methods resulted in a mean of 6.4 ± 1 mm/d. Diurnal meteorological fluctuations accounted for 36% of the total evaporation.

Simulations of the Summer Hydrometeorological Processes of Lake Kinneret

Lake Kinneret is a 168-km2 lake located in northern Israel. It provides about 50% of the drinking water consumed in this arid country. To manage correctly this vital water resource, it is essential to understand the various hydrometeorological processes that affect its water budget and, in particular, its evaporation. The complexity of the terrain in this region (varying from ≈2800 m to ≈−410 m within a short distance), combined with different types of soil and ground covers surrounding the lake, results in complicated microscale and mesoscale atmospheric motions, including sea, lake, and land breezes, as well as anabatic and katabatic winds. The Regional Atmospheric Modeling System (RAMS), a state-of-the-art nonhydrostatic model with two-way interactive multigrid nesting and four-dimensional data assimilation capabilities, was used, together with observations collected near the western and eastern shores of the lake, to study these processes. It was configured with two nested grids centered in the middle of the lake: 1) a coarse grid with 4 km × 4 km grid elements representing a 264 km × 240 km domain including Mount Hermon, the Dead Sea, the Golan Heights, and the Mediterranean coast; and 2) a fine grid with 1 km × 1 km grid elements covering a 42 km × 50 km domain. Two three-day periods in the summers of 1992 and 1993, during which hydrometeorological observations were available, were simulated. To account for synoptic conditions, the National Centers for Environmental Prediction–National Center for Atmospheric Research mandatory-level reanalyses produced every 6 h for these periods were assimilated by the model. The strength and timing of the various atmospheric motions that develop in that region and their interactions significantly affect the hydrometeorological processes of the lake, which are subject to important diurnal and spatial variations of wind intensity and direction, temperature, humidity, and fluxes. Since these processes have a strong feedback on the lake hydrodynamics and thermal structure, it is concluded that the development of a coupled lake–atmosphere model is needed to provide good estimates of lake evaporation when lake water surface temperatures are not available. Here, it is demonstrated that RAMS performs properly, given the particular complexity of the Lake Kinneret system and the uncertainty inherent in observations above turbulent water.

Estimation of lake evaporation from standard meteorological measurements: application to four Australian lakes in different climatic regions

A simple net heat model is presented for estimating monthly lake (or reservoir) evaporation using the Penman formulation with standard meteorological data: air and water-surface temperature, relative humidity, wind speed and sunshine hours. The model comprises simple expressions for the net solar and terrestrial radiation fluxes, or the net all-wave flux, at the water's surface, and for heat storage. The model is applied to four Australian lakes in semi-arid tropical, warm temperate, mediterranean and alpine climatic regions. The model predictions are found to agree well with mean monthly evaporation measurements for the four lakes. The net heat model was used with the Priestley- Taylor formulation, which does not require wind measurements, and its predictions were found to also agree well with the observations.

The Effect of Weather Variability on the Energy Balance of a Lake in the Hudson Bay Lowlands, Canada

Evaporation is an important component of the water balance of lakes in the Hudson Bay Lowlands, but the amount of summer evaporation in this area is not well known. Hourly summertime estimates of evaporation, from a small tundra lake near Churchill, Manitoba, are compared to equilibrium evaporation estimates of the Penman model. For the entire measurement period a = 1.35. For individual days a ranges from 1.0 to 2.0 and for individual hours from 1.0 to 4.0. Local advection is primarily responsible for the large fluxes of latent heat. The latent heat flux exceeds available radiant energy over the summer, with temperature inversions occurring over the lake on the majority of days. The advective enhancement of lake evaporation responds to daily weather variations. The classification of these variations will improve operational estimates of lake evaporation.

Practical Estimates of Lake Evaporation

Abstract Practical estimates of lake evaporation must rely on data that can be observed in the land environment. This requires the ability to take into account the changes in the temperature and humidity that occur when the air passes from the land to the lake environment. The complementary relationship between potential and areal evapotranspiration provides such a capability and is used herein, in combination with an approximate technique for taking into account subsurface heat storage changes, as the basis for formulating the complementary relationship lake evaporation (CRLE) model. Because it has a realistic basis, the CRLE model can utilize routine climatological data observed in the land environment to provide estimates of lake evaporation anywhere in the world with no need for locally calibrated coefficients. This potential is demonstrated by comparing model estimates with published water budget estimates for sixteen lakes in North America and one lake in East Africa.

Operational estimates of lake evaporation

The complementary relationship between areal and potential evapotranspiration takes into account the changes in the temperature and humidity of the air as it passes from a land environment to a lake environment. Minor changes convert the latest version of the complementary relationship areal evapotranspiration (CRAE) models to a complementary relationship lake evaporation (CRLE) model. The ability of the CRLE model to produce reliable estimates of annual lake evaporation from monthly values of temperature, humidity and sunshine duration (or global radiation) observed in the land environment with no locally optimized coefficients is tested against comparable water-budget estimates for 11 lakes in North America and Africa. Maps of annual lake evaporation and annual net reservoir evaporation (i.e. the difference between lake evaporation and areal evapotranspiration) for the part of Canada to the east of the Pacific Divide and for the southern U.S.A. are presented. An approximate routing technique, which takes into account the effects of depth and salinity on the seasonal pattern of monthly lake evaporation, is formulated and tested against comparable water-budget estimates for 10 lakes in North America and Africa. The results indicate that the CRLE model, with its associated routing technique, is much superior to the other techniques in current use that rely on climatological or pan observations in the land environment.