Investigating the decadal water level variability in Lake Uluabat, Türkiye: a complexity-based assessment of...

This study examines the long-term variations in the water-level time series of Lake Uluabat, located in western Türkiye, over the past six decades. Despite the decline in lake water level in recent years, the scarcity of reliable information remains a major problem in understanding this phenomenon. To overcome this limitation, monthly water-level observations spanning from October 1960 to September 2019 (708 months) were analyzed to explore temporal dynamics in trend, homogeneity, stationarity, frequency, persistence, entropy, and the reconstructed phase-space geometry. The analyses were conducted for the entire period (1960-2019) and six decadal intervals (i.e., 1960-1969, 1970-1979, 1980-1989, 1990-1999, 2000-2009, and 2010-2019) to identify regime shifts and decade-scale variability. The so-called autocorrelation function, mutual information, probability distributions, return period, and dimensional analysis were performed. Also, the teleconnections between lake-level fluctuations and 19 large-scale atmospheric-oceanic oscillation indices were investigated. Results indicated a persistent but gradually descending downward trend, accompanied by a rise in system entropy and short-term dependencies. This indicates increased complexity and dependence on external factors. So in a nutshell, the recent lake water-level properties indicate reduced degree of functionality and self-dependency of the hydrological regime. Yet, the temporal teleconnection between lake water level and the climatic oscillations showed stability. This indicates that the climate and the anthropogenic factors have a direct effect on the lake water level states, although in this case, the latter seems to have the upper hand.