Investigating the relationship between physical characteristics of watersheds and nonlinearity of daily streamflow processes

Abstract

Using time series models is one of the practical methods for simulation and prediction of hydrological data. But often, without examining linear or nonlinear system, common linear time-series models are used. And it is expected that streamflow nonlinearity is heavily influenced by physiographic characteristics of the watershed. In this study, using BDS test, nonlinearity of daily streamflow was examined, then its relationship with the watershed slope and area of hydrometric stations was examined. ADF test was used to test stationarity of data time series. The results of ADF test revealed that with the elimination of non-stationarity factors, streams' flow series become stationary. Also, BDS test results showed that flow was nonlinear. In examining the relationship between streamflow nonlinearity and watershed area, the results revealed that despite R2 = 0.91, nonlinearity of flow was in the significant relationship with the third power area. Regarding the relationship between streamflow nonlinearity and watershed slope, no significant relationship was found. It should be noted that the relationship between these two parameters and the intensity of nonlinearity is the novelty of this article.