Long-Term Trends in Annual Runoff and the Impact of Meteorological Factors in the Baiyangdian Watershed
The nonparametric Mann-Kendall method was used to detect long-term trends and determine the significant level of annual runoff observed at hydrologic stations in the Baiyangdian watershed. The Hurst exponent method was applied to analyze the sustainability of trends in annual runoff, which was then combined with the results of the Mann-Kendall test to examine characteristics of future trends in annual runoff. It was found that in general the upper reaches of the Baiyangdian watershed showed a more statistically significant decreasing trend in annual runoff than the lower reaches. The β value of annul runoff for the upper reaches was significantly smaller than that for the low reaches, which may be due to a larger magnitude of annual runoff in the lower reaches. The significant level and sustainability of the decreasing trend of the Shahe watershed located in the south of the Baiyangdian watershed were relatively less than those of the Tanghe and Jumahe watershed. This indicates that the annual runoff of the Shahe watershed exhibited a slower decreasing trend than the other two watersheds. The overall trend of annual runoff was decreasing and may maintain a consistently decreasing trend in the future, which can not only explain why watersheds and lakes across the Baiyangdian watershed are drying up but also be helpful for forecasting possible changes in runoff. These findings are beneficial in improving the understanding of the hydrological cycle and water resources management. The Pettitt change-point statistical method was used to determine hydrologic change points in annual runoff time series. The mean annual runoff before and after the change point were calculated, respectively. Comparison between them shows that the former was significantly larger than the later. An analysis focused on runoff change rates before and after the change year illustrates that the marked runoff change between the two periods may be influenced mainly by climate change in the Shahe watershed, while the essential factor dominating the annual runoff in the Jumahe watershed may be human activities. Subsequently, the authors compared air temperature and mean annual precipitation before and after the change point in the entire Baiyangdian watershed. Results indicate that the mean air temperature has increased about 1℃, which may play an important role in changing the evapotranspiration. Less precipitation may result in a reduction in the surface runoff, given a possible reduction in evapotranspiration. Mean annual precipitation decreased by about 56.6 mm when periods before the change year were compared with those after the change year. The decreased precipitation may be important to the significant reduction in surface runoff
NETL
NSTL
万方数据
维普
