Rasoul Jani - Department of Technical and Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.*Corresponding author
Mohammad Ali Ghorbani - Department of Civil Engineering, Tabriz University, Tabriz, Iran
Abolfazl Shamsaei - Department of Technical and Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

Adequate knowledge of rainfall behavior is important for proper planning and management of water resources and design of environment. In this study chaotic behavior of monthly rainfall in the Ramsar during January 1970 - December 2000 is investigated. The methods and indicators of chaos theory (power spectrum, average mutual information, false nearest neighbours, correlation dimension and largest Lyapunov exponents) were applied. The value of power spectrum (0.64)indicate that chaotic (fractal) behavior to the rainfall time series. The optimal delay time (4 month) and embedding dimension (13) are obtained from average mutual information and false nearest neighbours techniques, respectively. Optimal values are then used for the estimation of the correlation dimension and the largest Lyapunov exponent for inspecting possible signatures of chaotic dynamics. The low correlation dimension (2.82) suggest the presence of low-dimensional chaos; also imply that the rainfall dynamics are dominantly governed by three variables. The positive largest Lyapunov exponent value (0.0135) indicate a signature of chaos. These results give a positive indication towards considering rainfall as a chaotic system .

Chaos theory, Correlation dimension, Lyapunov exponent, Power spectrum, Ramsar