Spectral analysis of periodic behavior of Lake Urmia water level time series

The Urmia Lake is one of the important water bodies in the northwest of Iran that has a significant role in the economy and environment of the region. Recently, the lake is faced with a critical level reduction, which makes it important to evaluate the causes. In this regard understanding of the Lake's level behavior is necessary, which can be applied for mitigation measure to save it. This subject constructs objective of the present paper that applies the spectral analysis techniques to investigate harmonic periods of the Lake level time series. For this, a combination of Multi Taper Method of spectral estimation and Singular Spectral Analysis were implemented. The results showed significant long-term periods in time series. However due to limitation in the record length, the frequencies longer than about 20 years were applicable for the analyses. Also, comparing the reconstructed time series of harmonic series with the original time series showed that although, harmonic oscillations are effective on level behavior of the lake, but declines of the recent years are not completely describable by these periodicities.