Zongxue Xu

Monotonic trend and step changes in Japanese precipitation

For the purpose of detecting the possible long-term trends of Japanese precipitation, both parametric t-test and nonparametric Mann–Kendall and Mann–Whitney techniques are applied to the spatially averaged precipitation time series over Japan. The results indicate that although several step changes occurred in Japanese precipitation, the time series did not exhibit significant evidence of monotonic trend during the past century. When a step change is present, the number of observations required for detecting the trend of a given magnitude at a specified significance and power level is investigated with the power function of the t-test. Results indicate that if the magnitude of the step change reaches one or two times of its standard deviation, the previous 50-year of record together with 5 years or more of new data will be available for detecting the possible trend. This conclusion may be helpful for the detection of step changes in the regions where the precipitation has near-normal distributions.

Sustainability analysis for Yellow River water resources using the system dynamics approach

The water resource issue is one of the most significant problemsthat the Yellow River basin will face this century, and one which has received much attention by public and government for several years. Water authorities will face great challenges in meeting the in-stream flow requirements and providing more water for growing populations, industry and agriculture. In order toevaluate the sustainability of the water resource system inthe study area, an object-oriented system dynamics approachhas been used to develop a model for the water resourcessystem in the Yellow River basin, which is referred to asthe Water Resources System Dynamics (WRSD) model. It hasbeen developed for simulating a water resource system andcapturing the dynamic character of the main elements affectingwater demand and supply in the study area. For thebusiness-as-usual (BaU) scenario, the water demands in theYellow River basin are estimated 50.9, 56.5, and 59.5billion m3 for 2010, 2020, and 2030. The existing andpotential water supplies from surface water, aquifers andtreated waste-water are estimated, and potential waterdemands for domestic, industrial and agricultural uses areprojected. Various water supply and demand scenarios havethen been explored by changing variables and parameters,and the sustainability index of the water supply system isestimated for different sub-regions over various periods.

Impact of Climate Change on Water Resources in the Tarim River Basin

The plausible association between climate change and the variability of water resources in the Tarim River basin, west China is investigated in this study. The long-term trend of the hydrological time series including temperature, precipitation, and streamflow are detected by using both parametric and nonparametric techniques. The possible association between the El Niño/Southern Oscillation (ENSO) and these three kinds of time series are tested. This study enhances the knowledge of the climate change impact on water resources in the Tarim River basin. The conclusion obtained in this investigation shows that the temperature experienced a significant monotonic increase at the 5% level of significance during the past 50 yr, and precipitation also exhibited an upward tendency during the past several decades. A significant jump is also detected for both time series around 1986. This may be resulted from the possible impact of climate change, although the interior climate mechanism needs further investigation. Although precipitation and the streamflow from the headwater of the Tarim River exhibited significant increase, decreasing trend has been detected in the streamflow along the mainstream of the river. It implies that anthropogenic activities instead of the climate change dominated the streamflow cessation and the drying-up of the river. Results also showed that no significant association exists between the ENSO and the temperature, precipitation and streamflow in the study area. This conclusion shows that the water curtailment, river desiccation, and ecosystem deterioration in the Tarim River basin may be mainly resulted from the impact of human activities.

Assessing the effects of changes in land use and climate on runoff and sediment yields from a watershed in the Loess Plateau of China

The changes in runoff and sediment load in the Loess Plateau of China have received considerable attention owing to their dramatic decline during recent decades. In this paper, the impacts of land-use and climate changes on water and sediment yields in the Huangfuchuan River basin (HFCRB) of the Loess Plateau are investigated by combined usage of statistical tests, hydrological modeling, and land-use maps. The temporal trends and abrupt changes in runoff and sediment loads during 1954-2012 are detected by using non-parametric Mann-Kendall and Pettitt tests. The land-use changes between 1980 and 2005 are determined by using transition matrix analysis, and the effects of land-use and climate changes on water and sediment yields are assessed by using the Soil and Water Assessment Tool (SWAT) hydrological model and four scenarios, respectively. The results show significant decreasing trends in both annual runoff and sediment loads, whereas slightly decreasing and significantly increasing trends are detected for annual precipitation and air temperature, respectively. 1984 is identified as the dividing year of the study period. The land-use changes between 1980 and 2005 show significant effects of the Grain for Green Project in China. Both land-use change and climate change have greater impact on the reduction of sediment yield than that of water. Water and sediment yields in the upstream region show more significant decreases than those in the downstream region under different effects. The results obtained in this study can provide useful information for water resource planning and management as well as soil and water conservation in the Loess Plateau region.

System dynamics simulation model for assessing socio-economic impacts of different levels of environmental flow allocation in the Weihe River Basin, China

This study develops a complex system dynamics model (SD) reflecting interactions between water resources, Environmental Flow (EF) and socio-economy using SD software package “Vensim PLE”. The proposed model is employed to assess socio-economic impacts of different levels of EF allocation in the Weihe River Basin of China. Four alternative socio-economic growth patterns and four EF allocation schemes are designed to simulate those impacts. The results reveal that developed SD model performance well in reflecting the dynamic behavior of the system in the current study area. In the meanwhile, an optimal growth pattern considering both socio-economic growth and EF requirements are also found by comparing the different scenario simulation results.

A wavelet-neural network hybrid modelling approach for estimating and predicting river monthly flows

Abstract A wavelet-neural network (WNN) hybrid modelling approach for monthly river flow estimation and prediction is developed. This approach integrates discrete wavelet multi-resolution decomposition and a back-propagation (BP) feed-forward multilayer perceptron (FFML) artificial neural network (ANN). The Levenberg-Marquardt (LM) algorithm and the Bayesian regularization (BR) algorithm were employed to perform the network modelling. Monthly flow data from three gauges in the Weihe River in China were used for network training and testing for 48-month-ahead prediction. The comparison of results of the WNN hybrid model with those of the single ANN model show that the former is able to significantly increase the prediction accuracy. Editor D. Koutsoyiannis; Associate editor H. Aksoy Citation Wei, S., Yang, H., Song, J.X., Abbaspour, K., and Xu, Z.X., 2013. A wavelet-neural network hybrid modelling approach for estimating and predicting river monthly flows. Hydrological Sciences Journal, 58 (2), 374–389.

The nature and impact of climate change in the Challenge Program on Water and Food (CPWF) basins

In this article the authors assess the potential impacts of projected climate change on water, livelihoods and food security in the Basin Focal Projet basins. The authors consider expected change within the context of recently observed climate variability in the basins to better understand the potential impact of expected change and the options available for adaptation. They use multi-global circulation model climate projections for the AR4 SRES A2a scenario, downscaled and extracted for each basin. They find significant differences in the impacts (both positive and negative impacts) of climate change, between and within basins, but also find large-scale uncertainty between climate models in the impact that is projected.

Assessment of ecosystem health based on fish assemblages in the Wei River basin, China.

In the Wei River basin, the ecosystem is gradually deteriorating due to the rapid growth of the population and the development of economies. It is thus important to assess the ecosystem health and take measures to restore the damaged ecosystem. In this study, an index of biotic integrity (IBI) for fish was developed to aid the conservation of the ecosystem based on a calibration data set. An index of water and habitat quality (IWHQ) was calculated based on environmental variables and habitat quality (QHEI) to identify the environmental degradation in the studied sites. The least degraded sites (IWHQ ≤ 2; W1, W5, W10, W12, W13, W14, and W16) were chosen as the reference sites. Six metrics that are sensitive to environmental degradation were utilized to differentiate the reference and the impaired sites using statistical methods. These metrics included the number of species (P1), the total biomass (P2), the number of Cobitidae species (P8), the proportion of species in the middle and low tiers (P10), the proportion of individuals that were classified as sensitive species (P25), and number of individuals in the sample (P39). A continuous scoring method was used to score the six metrics, and four classes were defined to characterize the ecosystem health of the Wei River basin. The fact that the overall IBI scores were negatively correlated with the index of environmental quality (IWHQ) based on the validation data set indicated that the index should be useful for biomonitoring and the conservation of biodiversity. According to the results, more than half of the sites were classified as poor or very poor. The ecosystem health in the Wei River was better than that in the Jing River and the Beiluo River, and this study will be a great reference for water resources management and ecosystem restoration in the Wei River basin.

Evaluation of Gridded Precipitation Data for Driving SWAT Model in Area Upstream of Three Gorges Reservoir

Gridded precipitation data are becoming an important source for driving hydrologic models to achieve stable and valid simulation results in different regions. Thus, evaluating different sources of precipitation data is important for improving the applicability of gridded data. In this study, we used three gridded rainfall datasets: 1) National Centers for Environmental Prediction - Climate Forecast System Reanalysis (NCEP-CFSR); 2) Asian Precipitation - Highly-Resolved Observational Data Integration Towards Evaluation (APHRODITE); and 3) China trend - surface reanalysis (trend surface) data. These are compared with monitoring precipitation data for driving the Soil and Water Assessment Tool in two basins upstream of Three Gorges Reservoir (TGR) in China. The results of one test basin with significant topographic influence indicates that all the gridded data have poor abilities in reproducing hydrologic processes with the topographic influence on precipitation quantity and distribution. However, in a relatively flat test basin, the APHRODITE and trend surface data can give stable and desirable results. The results of this study suggest that precipitation data for future applications should be considered comprehensively in the TGR area, including the influence of data density and topography.

Incorporating inflow uncertainty into risk assessment for reservoir operation

An attempt of using stochastic hydrologic technique to assess the intrinsic risk of reservoir operation is made in this study. A stochastic simulation model for reservoir operation is developed. The model consists of three components: synthetic generation model for streamflow and sediment sequences, one-dimensional delta deposit model for sediment transport processes in reservoirs, and simulation model for reservoir operation. This kind of integrated simulation model can be used to simulate not only the inflow uncertainty of streamflow and sedimentation, but also the variation in operation rules of reservoirs. It is herein used for the risk assessment of a reservoir, and the simulation is performed for different operation scenarios. Simulation for the 100-year period of sediment transport and deposition in the river-reservoir system indicates that the navigation risk is much higher than that of hydropower generation or sediment deposition in the reservoir. The risk of sediment deposition at the river-section near the backwater profile is also high thereby the navigation at the river-segment near this profile takes high risk because of inadequate navigation depth.