Detecting determinism and nonlinearity in river-flow time series

The temporal evolution of river-flow dynamics is investigated using methods from nonlinear time series analysis. After a discussion on the possible sources of nonlinear deterministic components, different methods for the detection of nonlinear and deterministic components in river flow time series are illustrated and the application to three river-flow time series from basins of different dimensions and characteristics is presented. All the results of different nonlinear techniques show noticeable evidence of determinism and nonlinearity at high discharge values, while at low discharge values, and especially during recessions, the series seem to be the result of a mostly linear dynamics. The complexity of the dynamics and the degree of nonlinearity are also discussed in relation to the basin dimensions and the kind of hydroclimatic regime.