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Title: AGGREGATION AND SAMPLING IN DETERMINISTIC CHAOS: IMPLICATIONS FOR CHAOS IDENTIFICATION IN HYDROLOGICAL PROCESSES

Author
item SALAS, J - COLORADO STATE UNIVERSITY
item KIM, H - INHA UNIVERSITY
item BURLANDO, P - ETH HOENGGERBERG
item Green, Timothy

Submitted to: Nonlinear Processes in Geophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2005
Publication Date: 6/7/2005
Citation: Salas, J.D., Kim, H.S., Burlando, P., Green, T.R. 2005. Aggregation and sampling in deterministic chaos: implications for chaos identification in hydrological processes. Agronomy Abstracts. Nonlinear Processes in Geophysics, 12, 557-567, 2005.

Interpretive Summary: A review of the literature reveals conflicting results regarding the existence and inherent nature of chaos in hydrological processes such as precipitation and streamflow, i.e. whether they are chaotic (low-dimensional deterministic) or stochastic. In this paper, we examine the effects that certain types of transformations, such as aggregation and sampling, may have on the identification of the dynamics of the underlying system. First, we investigate the dynamics of daily streamflows for two rivers in Florida, one with strong surface and groundwater storage contributions and the other with a lesser basin storage contribution. The river with the stronger basin storage contribution departs significantly from the behavior of a chaotic system, while the departure is less significant for the river with the smaller basin storage contribution. We pose the hypothesis that the chaotic behavior depicted in continuous precipitation fields or small time-step precipitation series becomes less identifiable as the aggregation (or sampling) time step increases. Similarly, because streamflows result from a complex transformation of precipitation that involves accumulating and routing excess rainfall throughout the basin and adding surface and groundwater flows, the end result may be that streamflows at the outlet of the basin depart from chaotic behavior. We also investigate the effect of aggregation and sampling using series derived from the Lorenz equations and show that, as the aggregation and sampling scales increase, the chaotic behavior deteriorates.

Technical Abstract: A review of the literature reveals conflicting results regarding the existence and inherent nature of chaos in hydrological processes such as precipitation and streamflow,i.e. whether they are low dimensional chaotic or stochastic.This issue is examined further in this paper, particularly the effect that certain types of transformations, such as aggregation and sampling, may have on the identification of the dynamics of the underlying system. First, we investigate the dynamics of daily streamflows for two rivers in Florida, one with strong surface and groundwater storage contributions and the other with a lesser basin storage contribution. Based on estimates of the delay time, the delay time window, and the correlation integral, our results suggest that the river with the stronger basin storage contribution departs significantly from the behavior of a chaotic system, while the departure is less significant for the river with the smaller basin storage contribution. We pose the hypothesis that the chaotic behavior depicted on continuous precipitation fields or small time-step precipitation series becomes less identifiable as the aggregation (or sampling) time step increases. Similarly, because streamflows result from a complex transformation of precipitation that involves accumulating and routing excess rainfall throughout the basin and adding surface and groundwater flows, the end result may be that streamflows at the outlet of the basin depart from low dimensional chaotic behavior. We also investigate the effect of aggregation and sampling using series derived from the Lorenz equations and show that, as the aggregation and sampling scales increase, the chaotic behavior deteriorates and eventually ceases to show evidence of low dimensional determinism.