Abstract. Under the background of global climate change and local anthropogenic activities, multiple driving forces have introduced various nonstationary components into lowflow 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 P , mean frequency of precipitation events λ, temperature T , potential evapotranspiration (EP), climate aridity index AI EP , base-flow index (BFI), recession constant K and the recession-related aridity index AI K ). 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 AI K is of the highest relative importance among these four variables, followed by IAR, BFI and AI EP . 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.

The femtosecond laser micromachining of transparent optical materials offers a powerful and feasible solution to fabricate versatile photonic components towards diverse applications. In this work, we report on a new design and fabrication of ridge waveguides in LiNbO3 crystal operating at the mid-infrared (MIR) band by all-femtosecond-laser microfabrication. The ridges consist of laser-ablated sidewalls and laser-written bottom low-index cladding tracks, which are constructed for horizontal and longitudinal light confinement, respectively. The ridge waveguides are found to support good guidance at wavelength of 4 μm. By applying this configuration, Y-branch waveguiding structures (1 × 2 beam splitters) have been produced, which reach splitting ratios of ∼1:1 at 4 μm. This work paves a simple and feasible way to construct novel ridge waveguide devices in dielectrics through all-femtosecond-laser micro-processing.

The design of stormwater drainage infrastructure in urban areas in China is based on the statistical stationary assumption of probability distribution of extreme rainfall, which is being increasingly challenged by climate change. However, quantitative assessment of the performance of urban drainage systems in response to climate change with the latest emission scenarios of the Coupled Model Intercomparison Project Phase 5 in China is quite limited. This study aims to investigate potential changes of extreme rainfall and their influence on drainage infrastructure in a representative urban area in Wuhan city, China. The Storm Water Management Model is established to investigate the response of drainage infrastructure to future design rainfall. It is found that the probability distribution of extreme rainfall for two historical sub‐periods (1961–1985 and 1986–2005) has changed, especially in the head and tail of the frequency curves. Furthermore, the design rainfall with return periods of 2, 3, 4 and 5 years increases more significantly than those of 10 and 20 years. Consequently, the incapability of the current drainage infrastructure in the study area is aggravated. Moreover, the results of SWMM modelling provide detailed information about the performance of current drainage infrastructure, which can provide technical support for future modifications of the current drainage infrastructure of the study area. © 2018 John Wiley & Sons, Ltd.

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The predictions of flood hazard over the design life of a hydrological project are of great importance for hydrological engineering design under the changing environment. The concept of a nonstationary flood hazard has been formulated by extending the geometric distribution to account for time-varying exceedance probabilities over the design life of a project. However, to our knowledge, only time covariate is used to estimate the nonstationary flood hazard over the lifespan of a project, which lacks physical meaning and may lead to unreasonable results. In this study, we aim to strengthen the physical meaning of nonstationary flood hazard analysis by investigating the impacts of climate change and population growth. For this purpose, two physical covariates, i.e., rainfall and population, are introduced to improve the characterization of nonstationary frequency over a given design lifespan. The annual maximum flood series of Xijiang River (increasing trend) and Weihe River (decreasing trend) are chosen as illustrations, respectively. The results indicated that:(1) the explanatory power of population and rainfall is better than time covariate in the study areas;(2) the nonstationary models with physical covariates possess more appropriate statistical parameters and thus are able to provide more reasonable estimates of a nonstationary flood hazard; and (3) the confidences intervals of nonstationary design flood can be greatly reduced by employing physical covariates. Therefore, nonstationary flood design and hazard analysis with physical covariates are recommended in changing environments.

We report on the fabrication of ring-shaped waveguides operating at the telecommunication band in a cubic BiGeO (BGO) crystal by using technique of femtosecond laser writing. In the regions of laser written tracks in BGO crystal, positive refractive index is induced, resulting in so-called Type I configuration. The modal profiles are within the designed track cladding with ring-shaped geometries, which are analogous to circular optical lattices. The homogenous guidance along both TE and TM polarizations has been obtained at telecommunication wavelength of 1.55 μm. Both straight and S-curved waveguiding structures have been produced with ring-shaped configurations. This work paves the way to fabricate complex photonic networks for telecommunications by using ring-shaped waveguides in compact chips.

Abstract:16 Under the background of global climate change and local anthropogenic activities, multiple 17 driving forces have introduced a variety of non-stationary components into low-flow series. This 18 has led to a high demand on low-flow frequency analysis that considers nonstationary conditions 19 for modeling. In this study, a nonstationary framework of low-flow frequency analysis has been 20 developed on basis of the Generalized Linear Model (GLM) to consider time-varying distribution 21 parameters. In GLMs, the candidate explanatory variables to explain the time-varying parameters 22 are comprised of the eight measuring indices of the climate and catchment conditions in low flow 23 generation, i.e., total precipitation (P), mean frequency of precipitation events (λ), temperature (T), 24 potential evapotranspiration (ET), climate aridity index (AIET), base-flow index (BFI), recession 25 constant (K) and the recession-related aridity index (AIK). This framework was applied to the 26 annual minimum flow series of both Huaxian and Xianyang gauging stations in the Weihe River, 27China. Stepwise regression analysis was performed to obtain the best subset of those candidate 28 explanatory variables for the final optimum model. The results show that the inter-annual 29 variability in the variables of those selected best subsets plays an important role in modeling 30 annual low flow series. Specifically, analysis of annual minimum 30-day flow in Huaxian shows 31 that AIK is of the highest relative importance among the best subset of eight candidates, followed 32 by BFI and AIET. The incorporation of multiple indices related to low-flow generation permits 33

We report on the design and fabrication of straight and S-curved waveguides in neodymium-doped yttrium aluminate (Nd:YAP) crystal by using direct femtosecond laser writing. These S-curved channel waveguides are based on the hexagonal optical-lattice-like and depressed cladding geometry. For each type waveguide, S-curves with three lateral offsets of 50 µm, 100 µm, and 150 µm are implemented. These waveguides are with good guiding properties and low bending losses. With S-curved waveguide as laser cavity, dual-wavelength, 31.6 GHz waveguide laser operating at 1064 nm and 1079 nm have been demonstrated based on MoS 2 as a saturable absorber. This work paves the way to develop new on-chip ultrafast laser sources based on femtosecond laser inscribed S-curved waveguides.