Detection of abrupt shift and non-parametric analyses of trends in runoff time series in the Dez river basin

Abstract

The present study aims to investigate the homogeneity of runoff time series and also to review the existence of trends in Tale Zang hydrometric station (the hydrometric station at the inflow into the Dez reservoir) runoff, using 61 years (1956–2016) daily recorded data. The Pettit test, which is a common method in investigating the homogeneity of time series, was used to identify change points. Both Mann-Kendall and auto-correlated Mann-Kendall tests were applied to analyze the existence or non-existence of trends in each annual, seasonal, and monthly time series observed in a runoff. In time series, significant trends at the 95% level of confidence were recognized, upper and lower limit values were presented for Sen's slope and it was tested for the increasing or decreasing trends in nature. Based on the results of this study, the significant change point at the 95% level of confidence was recognized in the annual, spring, summer, autumn, March, May, June, July, August, September, and October data sets in 1997,1997, 1999, 1997, 1999, 1999, 1999, 1997, 2000, 2007 and 2008, respectively. Analyzing the existence of a trend at the 95% level of confidence indicated that in spring, and in March, September, and October, for both Mann-Kendall and auto-correlated Mann-Kendall tests, the trend is significant and additive until the change point. HIGHLIGHTS Investigating the changes in long term runoff time series at the Tale Zang hydrometric station for the first time.; Investigating the magnitude of the change point or trend at the 95% level of confidence.; Studying the existence or nonexistence of trends before and after the change point of confidence.; Determining the upper and lower limits of Sen's slope.; Assisting water resource planners to make appropriate decisions.;

Keywords

• non-parametric test
• pettit test
• runoff
• sen's slope