Abstract
Integration of remote sensing data sets from multiple satellites is tested to simulate water storage variation of Lake Ziway, Ethiopia for the period 2009-2018. Sixty Landsat ETM+/OLI images served to trace temporal variation of lake surface area using a water extraction index. Time series of lake levels were acquired from two altimetry databases that were validated by in-situ lake level measurements. Coinciding pairs of optical satellite based lake surface area and radar altimetry based lake levels were related through regression and served for simulating lake storage variation. Indices for extracting lake surface area from images showed 91–99 % overall accuracy. Lake water levels from the altimetry products well agreed to in-situ lake level measurements with R2 = 0.92 and root mean square error of 11.9 cm. Based on this study we conclude that integrating satellite imagery and radar altimetry is a viable approach for frequent and accurate monitoring of lake water volume variation and for long-term change detection. Findings indicate water level reduction (4 cm/annum), surface area shrinkage (0.08km2/annum) and water storage loss (20.4Mm3/annum) of Lake Ziway (2009–2018).
Highlights
Worldwide many lakes are dramatically dwindling or completely drying up as shown in Pekel et al (2016); Wurtsbaugh et al (2017) and Tan et al (2018)
The accuracy of the three water indices (NDWI, Modified NDWI (MNDWI) and Automated Water Extraction Index (AWEI)) was evaluated by use of five hundred ground control points and by inter-comparison of the lake extent extracted from the indices (Fig. 3)
Visual interpretation of lake surface area using the high resolution image (HRI) indicated that MNDWI and AWEI best distinguished the water surface from the adjacent land features
Summary
Worldwide many lakes are dramatically dwindling or completely drying up as shown in Pekel et al (2016); Wurtsbaugh et al (2017) and Tan et al (2018). Lake Urmia in Iran lost 86 % of its surface area and reached only 0.83 % of its original storage within 15 years (Jeihouni et al, 2017). In Tanzania, the surface area of Lake Manyara shrank by 94 % in a period covering only eleven years (Deus and Gloaguen, 2013). Lake Mead in USA lost nearly 40 % of its surface area within a decade (Forsythe et al, 2012). Water level of Lake Qinghai in China gradually declined over the past half of a century at a rate of 8 cm per annum (Chang et al, 2017). There is urgent need to evaluate the change of lake water storage and to provide evidence for better management of the lake
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