Journal of Environmental Biology

Analysis of the climate variability on Lake Nasser evaporation

based on the Bowen ratio energy budget method

 

Author Details

 

Mohamed Elsawwaf (Corresponding author)

Hydraulics Laboratory, Department of Civil Engineering, Katholieke Universiteit Leuven, Kasteelpark

Arenberg 40, 3001 Heverlee

Water Resources Research Institute, National Water Research Center, El-Qanater El-Khiria. 13621, 

Egypt

e-mail: ahmed_karem40@yahoo.com

Patrick Willems

Hydraulics Laboratory, Department of Civil Engineering, Katholieke Universiteit Leuven, Kasteelpark

Arenberg 40, 3001 Heverlee, Belgium

 

Publication Data

Paper received:

25 October 2010

 

Revised received:

05 July 2011

 

Accepted:

30 July 2011

 

Abstract

Variations in lake evaporation have a significant impact on the energy and water budgets of lakes. Understanding these variations and the role of climate is important for water resources management as well as predicting future changes in lake hydrology as a result of climate change. This study presents a comprehensive, 10-year analysis of seasonal, intraseasonal, and interannual variations in lake evaporation for Lake Nasser in South Egypt. Meteorological and lake temperature measurements were collected from an instrumented platform (Raft floating weather station) at 2 km upstream of the Aswan High Dam. In addition to that, radiation measurements at three locations on the lake: Allaqi, Abusembel and Arqeen (respectively at 75, 280 and 350 km upstream of the Aswan High Dam) are used. The data were analyzed over 14-day periods from 1995 to 2004 to provide bi-weekly energy budget estimates of evaporation rate. The mean evaporation rate for lake Nasser over the study period was 5.88 mm day^-1, with a coefficient of variation of 63%. Considerable variability in evaporation rates was found on a wide range of timescales, with seasonal changes having the highest coefficient of variation (32%), followed by the intraseasonal (28%) and interannual timescales (11.6%; for summer means). Intraseasonal changes in evaporation were primarily associated with synoptic weather variations, with high evaporation events tending to occur during incursions of cold, dry air (due, in part, to the thermal lag between air and lake temperatures). Seasonal variations in evaporation were largely driven by temperature and net energy advection, but are out-of-phase with changes in wind speed. On interannual timescales, changes in summer evaporation rates were strongly associated with changes in net energy advection and showed only moderate connections to variations in temperature or humidity.

 

Key words

Lake Nasser, Energy budget, Climate variability, Bowen ratio energy budget (BREB)

 

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