Multiple causes of nonstationarity in the Weihe annual low-flow series

Xiong, Bin; Xiong, Lihua; Chen, Jie; Xu, Chong-Yu; Li, Lingqi

Under the background of global climate change and local anthropogenic activities, multiple driving forces have introduced various nonstationary components into low-flow series. This has led to a high demand on low-flow frequency analysis that considers nonstationary conditions for modeling. In this study, through a nonstationary frequency analysis framework with the generalized linear model (GLM) to consider time-varying distribution parameters, the multiple explanatory variables were incorporated to explain the variation in low-flow distribution parameters. These variables are comprised of the three indices of human activities (HAs; i.e., population, POP; irrigation area, IAR; and gross domestic product, GDP) and the eight measuring indices of the climate and catchment conditions (i.e., total precipitation inline-formulaP, mean frequency of precipitation events inline-formulaλ, temperature inline-formulaT, potential evapotranspiration (EP), climate aridity index AIinline-formulaEP, base-flow index (BFI), recession constant inline-formulaK and the recession-related aridity index AIinline-formulaK). This framework was applied to model the annual minimum flow series of both Huaxian and Xianyang gauging stations in the Weihe River, China (also known as the Wei He River). The results from stepwise regression for the optimal explanatory variables show that the variables related to irrigation, recession, temperature and precipitation play an important role in modeling. Specifically, analysis of annual minimum 30-day flow in Huaxian shows that the nonstationary distribution model with any one of all explanatory variables is better than the one without explanatory variables, the nonstationary gamma distribution model with four optimal variables is the best model and AIinline-formulaK is of the highest relative importance among these four variables, followed by IAR, BFI and AIinline-formulaEP. We conclude that the incorporation of multiple indices related to low-flow generation permits tracing various driving forces. The established link in nonstationary analysis will be beneficial to analyze future occurrences of low-flow extremes in similar areas.

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Xiong, Bin / Xiong, Lihua / Chen, Jie / et al: Multiple causes of nonstationarity in the Weihe annual low-flow series. 2018. Copernicus Publications.

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