Abstract
In this paper, the water level fluctuations of eight Ethiopian Rift Valley lakes were analyzed for their hydrological stability in terms of water level dynamics and their controlling factors. Long-term water balances and morphological nature of the lakes were used as bases for the analyses. Pettit’s homogeneity test and Mann–Kendall trend analysis were applied to test temporal variations of the lake levels. It is found that the hydrological stability of most of the Ethiopian Rift Valley lakes is sensitive to climate variability. In terms of monotonic trends, Lake Ziway, Hawassa, Abaya and Beseka experienced significant increasing trend, while Ziway, Langano and Chamo do not. In addition, homogeneity test revealed that Lake Hawassa and Abaya showed significant upward shift around 1991/1992, which was likely caused by climate anomalies such as the El Niño / Southern Oscillation (ENSO) phenomena. Lake Abiyata is depicted by its significant decreasing monotonic trend and downward regime shift around 1984/1985, which is likely related to the extended water abstraction for industrial consumption.
Highlights
Water level variability of a given lake results from water exchange characteristics within its watershed [1]
This study aims to investigate the hydrological nature of Main Ethiopian Rift Valley lakes by assessing their long-term water balances; their morphological characteristics; and analyzing their time series data of water level records
Assuming the fundamental similarity of all lakes, the study adopted four different approaches to estimate the natural responses of the lakes. These techniques of characterizing the lake level regime are suggested by Szesztay [32] based on long-term water balances; Litinskaya [33] based on morphological nature of lakes; Pettit [34] to test for the occurrences of significant regime shift (Homogeneity test); and Mann [35] and Kendall [36] test for monotonic trend test
Summary
Water level variability of a given lake results from water exchange characteristics within its watershed [1]. Lake levels fluctuate naturally in response to climatic and hydrological factors within natural amplitudes [2] as far as they are undisturbed by external forces such as climate anomalies or anthropogenic factors. The seasonal and annual water level fluctuation of lakes is a common phenomenon in every lake. Such fluctuations are usually due to the differences between precipitation and evaporation at specific season [4]. These dynamics are controlled by the balance between inputs and outputs of water, which are in turn controlled by the hydrological processes [5]
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