Evaluating the seasonal non-stationarity in the Wei River Basin

Due to the impact of changing climate and human activities on hydrology, non-stationary research is becoming more popular. In the Wei River Basin, which is the largest tributary of the Yellow River, non-stationary has been studied for decades and has found non-stationary signals in discharge and precipitation records. However, these studies have mainly focused on the annual time series and ignored the seasonal signal.

In this study, to investigate the non-stationarity more comprehensively, two non-stationary tests have been applied including the Mann-Kendall test and the Heuristic segmentation algorithm. These tests were applied to runoff time series from 12 catchments and catchment averaged precipitation and temperature time series derived from 114 meteorological stations. Like other studies, our results, show that on the annual timescale, non-stationary signals (multiple change points and decreasing trends) are found in the runoff time series on most catchments along the mainstem, while the runoff time series of the Beiluo catchment does not show any non-stationarity signal. However, our results show that there is clearly a seasonal difference with change points occurring at contrasting times. Among all time series, about 40% show only single nonstationary signals (trend or change point), while the remainder exhibit multiple signals indicating the importance of using multiple tests. While the results show that non-stationary signals exist in all time series, further work is needed to quantify if or to what level are meteorological variables the driver of non-stationary signals in the runoff time series.