assessing the effect of soi and nao indices on lake urmia water level variations, application of spectral analysis

abstract the urmia lake as an important water body in the northwest of iran, recently is faced with a critical level reduction, which makes it important to evaluate the causes. in this regard understanding of the lake's behavior and assessing effect of tele-connections on lake level oscillations is necessary. this subject constructs objective of the present paper that applies the spectral analysis techniques in which a combination of multi taper method of spectral estimation and singular spectral analysis were implemented to investigate harmonic periods of the lake level. also coherency analysis between lake level time series and soi and nao indices based on cross spectral estimation were done. the results showed that water level reduction of lake urmia in recent years and the increase of water level in 1994 to 1999 cannot be simulated by periodic behavior of lake urmia. but the 4.5 year oscillations of lake urmia water level shows significant coherency with soi and nao indices and the effect of these climate forcing can explain periodic behavior of lake urmia to a high extent.