Surface Energy Balance of Fresh and Saline Waters: AquaSEBS

Ahmed Abdelrady,Zoltán Vekerdy,Mhd Salama,Joris Timmermans

doi:10.3390/rs8070583

Abstract

Current earth observation models do not take into account the influence of water salinity on the evaporation rate, even though the salinity influences the evaporation rate by affecting the density and latent heat of vaporization. In this paper, we adapt the SEBS (Surface Energy Balance System) model for large water bodies and add the effect of water salinity to the evaporation rate. Firstly, SEBS is modified for fresh-water whereby new parameterizations of the water heat flux and sensible heat flux are suggested. This is achieved by adapting the roughness heights for momentum and heat transfer. Secondly, a salinity correction factor is integrated into the adapted model. Eddy covariance measurements over Lake IJsselmeer (The Netherlands) are carried out and used to estimate the roughness heights for momentum (~0.0002 m) and heat transfer (~0.0001 m). Application of these values over the Victoria and Tana lakes (freshwater) in Africa showed that the calculated latent heat fluxes agree well with the measurements. The root mean-square of relative-errors (rRMSE) is about 4.1% for Lake Victoria and 4.7%, for Lake Tana. Verification with ECMWF data showed that the salinity reduced the evaporation at varying levels by up to 27% in the Great Salt Lake and by 1% for open ocean. Our results show the importance of salinity to the evaporation rate and the suitability of the adapted-SEBS model (AquaSEBS) for fresh and saline waters.

Highlights

Evaporation from large water bodies, including inland waters, has a dominant role in the hydrological cycle [1,2]
Surface Energy Balance System (SEBS) is a one-source physical model which is applicable on a large scale, as it incorporates the physical state of the surface and the aerodynamic resistances for daily evaporation estimation [6]
AquaSEBS model was developed based on the SEBS surface energy balance model to estimate the heat fluxes over fresh and saline water bodies

Summary

Introduction

Evaporation from large water bodies, including inland waters, has a dominant role in the hydrological cycle [1,2]. Accurate monitoring of this evaporation is of high importance. This evaporation greatly varies due to large variations in ocean water characteristics, such as turbidity and salinity [1]. Saline water has lower evaporation rates than fresh water, regardless of the chemical composition of the salt. This reduced evaporation leads to an increase in the energy available for the warming up of the water, and, to the energy transfer from the water surface to the atmosphere by other processes, such as sensible heat [8]

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Conclusion