The Falling Lake Victoria Water Level: GRACE,TRIMM and CHAMP Satellite Analysis of the Lake Basin |
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Authors: | Joseph L Awange Mohammad A Sharifi Godfrey Ogonda Jens Wickert Erik W Grafarend Monica A Omulo |
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Affiliation: | (1) Western Australia Center of Geodesy &; The Institute for Geoscience Research, Department of Spatial Sciences, Curtin University of Technology, Bentley, Australia;(2) Surveying and Geomatics Engineering Department, Faculty of Engineering, University of Tehran, Tehran, Iran;(3) Institute of Navigation, Stuttgart University, Geschwister-Scholl Str. 24D, 70174 Stuttgart, Germany;(4) Department 1: Geodesy and Remote Sensing, GeoForschungsZentrum Potsdam (GFZ), Telegrafenberg, 14473 Potsdam, Germany;(5) Department of Geodesy and Geoinformatics, Stuttgart University, Geschwister-Scholl Str. 24D, 70174 Stuttgart, Germany;(6) Department of Environment, Maseno University, Private Bag, Maseno, Kenya |
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Abstract: | In the last 5 years, Lake Victoria water level has seen a dramatic fall that has caused alarm to water resource managers.
Since the lake basin contributes about 20% of the lakes water in form of discharge, with 80% coming from direct rainfall,
this study undertook a satellite analysis of the entire lake basin in an attempt to establish the cause of the decline. Gravity
Recovery And Climate Experiment (GRACE), Tropical Rainfall Measuring Mission (TRMM) and CHAllenging Minisatellite Payload
(CHAMP) satellites were employed in the analysis. Using 45 months of data spanning a period of 4 years (2002–2006), GRACE
satellite data are used to analyse the variation of the geoid (equipotential surface approximating the mean sea level) triggered
by variation in the stored waters within the lake basin. TRMM Level 3 monthly data for the same period of time are used to
compute mean rainfall for a spatial coverage of .25°×.25° (25×25 km) and the rainfall trend over the same period analyzed.
To assess the effect of evaporation, 59 CHAMP satellite’s occultation for the period 2001 to 2006 are analyzed for tropopause
warming. GRACE results indicate an annual fall in the geoid by 1.574 mm/year during the study period 2002–2006. This fall
clearly demonstrates the basin losing water over these period. TRMM results on the other hand indicate the rainfall over the
basin (and directly over the lake) to have been stable during this period. The CHAMP satellite results indicate the tropopause
temperature to have fallen in 2002 by about 3.9 K and increased by 2.2 K in 2003 and remained above the 189.5 K value of 2002.
The tropopause heights have shown a steady increase from a height of 16.72 m in 2001 and has remained above this value reaching
a maximum of 17.59 km in 2005, an increase in height by 0.87 m. Though the basin discharge contributes only 20%, its decline
has contributed to the fall in the lake waters. Since rainfall over the period remained stable, and temperatures did not increase
drastically to cause massive evaporation, the remaining major contributor is the discharge from the expanded Owen Falls dam. |
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Keywords: | Lake Victoria Water balance Tropopause temperature Rainfall CHAMP GRACE TRMM |
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