Low-frequency sea level changes in the Caspian Sea: long-term and seasonal trends

Abstract

The analysis of seasonal and long-term changes of the Caspian Sea level examined from historical long time tide gauge data in order to consider the influence of climate factors on sea level changes in this lake system using spectral analysis method. The major peak at spectra corresponds to the annual cycle and semiannual oscillations peak is located at next vigorous. Effects of different global and regional factors on lake level changes are investigated by signal processing methods. Results show that annual cycle of Siberian High and Volga River discharge have the considerable effects on the Caspian Sea level changes in global and regional scales, respectively. Analyzing of seasonal cycle revealed that Volga river discharge is significant on sea level fluctuations by 1-month lag in northern and central sub-basins and 2 months delay for southern sub-basin. The results of long-term cycle show ascending trend of evaporation in Caspian central sub-basin, which it is the main driver of decreasing trend of the Caspian Sea level since 1990s.