A linear/non-linear hybrid time-series model to investigate the depletion of inland water bodies
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A linear/non‑linear hybrid time‑series model to investigate the depletion of inland water bodies Babak Zolghadr‑Asli1 · Maedeh Enayati1 · Hamid Reza Pourghasemi2 · Mojtaba Naghdyzadegan Jahromi3 · John P. Tiefenbacher4 Received: 26 August 2020 / Accepted: 3 November 2020 © Springer Nature B.V. 2020
Abstract Changing climate and human interference with natural phenomena are causing unprecedented changing patterns in hydro-climatic variables. These changes can manifest as dynamic changes of the stochastic properties of the datasets over time, which pose challenges for conventional time-series modeling. These datasets are dynamic in nature, even when trend and seasonality components are eliminated. Shrinking lakes are among the most notable examples of hydro-climatic-driven phenomena. This study demonstrates a framework that can capture the underlying dynamic and non-stationary structure of such environments using a case study of Maharlou Lake, Iran. To that end, a hybrid time-series model was developed to account for volatility in the data [i.e., SARIMA (1,1,2) × (1,1,2)12/ GARCH(1,0)]. A series of statistical tests (i.e., augmented Dickey–Fuller test, the LjungBox test, the heteroskedasticity test, and the two-sample Kolmogorov–Smirnov test) were used to create, calibrate, and assess the model in the 95% confidence interval. The results indicate the decline and depletion of the lake. This reduction manifests as a general downward trend and a widening gap between the lake’s intra-annual fluctuations. The changes could be an alarming signal, as this saline lake could be mimicking the tragic fate of similar inland water bodies like Lake Urmia or the Aral Sea. Keywords Time-series analysis · SARIMA · GARCH · Shrinking lakes · Augmented Dickey–Fuller test · Ljung-Box test · Heteroskedasticity test · Kolmogorov–Smirnov test
1 Introduction In terms of volume, 44% of all the lakes are categorized as large and saline (Messager et al. 2016). Recent reports, however, indicate that Earth’s saline lakes are shrinking at an alarming rate, and the number of such cases is increasing rapidly (Jones and Fleck 2020). This epidemic could jeopardize habitats and economic benefits that are associated with these lakes and may ultimately threaten human health as well (Wurtsbaugh et al. 2017). While each of these reported cases is unique and, as such, it is difficult to pinpoint specific * Babak Zolghadr‑Asli [email protected] Extended author information available on the last page of the article
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causes that would explain them all (Khazaei et al. 2019), several reasons have been offered to explain this phenomenon. In some cases, the degradation of some lakes has been linked to human interference [e.g., Alemaya and Hora-Kilole Lakes, Ethiopia (Lemma 2003), Dead Seas, West Bank (Yechieli et al. 2006), Ebinur Lake, China (Zhang et al. 2015), and Lake Corangamite, Australia (Timms 2005)]. The Aral Sea, Kazakhstan, which suffered a 74% reduction in surface area due to water diver
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