Analysis of monthly streamflow series of the Litani River (Lebanon) by using spectral and topological methods

This study aims at investigating several dynamical parameters of the monthly variability of eight streamflow time series, recorded at different stations along the major courses and springs of the Litani River (Lebanon). The contribution of the annual periodicity to the total variance of the series depends on the geomorphological characteristics of the measuring sites. The long-term trend of five northern stations is more or less uniform, while that of the remaining southern three is characterized by a decreasing behaviour. The long-term trend of each streamflow series is, furthermore, featured by the presence of several peaks, mostly due to extreme rainfall events. Applying to the long-term trends the horizontal visibility graph, it was found that the North Atlantic Oscillation index could be a significant forcing of the complex fluctuations of the streamflows.