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The complexity of agricultural water management practices has challenged researchers attempting to determine how hydrological pathways affect water and nitrogen (N) losses. Field experiments in a typical rice agricultural catchment in the Zhanghe Irrigation District in China were conducted in 2014 and 2015 to evaluate and quantify the connections between hydrological pathways and water and N losses. Four water management periods--namely, the irrigation period (IP), the rainfall period (RP), the normal-drainage period (DP), and the nonirrigation-drainage period (NP)--were defined based on climate conditions and artificial irrigation and drainage periods. The experimental results indicated that most water and N losses occurred in DP and RP and that lateral seepage and tailwater were the main sources of the observed drainage. Low average concentrations of ammonia N (NH4+--N, 0.373 mg L-1) and nitrate N (NO3---N, 0.285 mg L-1) and low proportions of dissolved N (42.2-54.0%) were detected in association with green manure application, whereas the average concentration of total N (TN, 1.376 mg L-1) was relatively high, which resulted in slight N pollution in the studied agricultural area. The concentrations and proportions of dissolved N were greastest in DP and RP. The average daily mass fluxes of NH4+--N, NO3---N, and TN were 0.027, 0.020, and 0.095 kg ha-1 day-1, respectively, and the magnitudes in DP and RP were significantly greater than those in IP and NP. The average concentrations of NH4+--N, NO3---N, and TN were not correlated to drainage discharge according to a Pearson correlation analysis, whereas a power function can quantify the relationship between N mass fluxes and discharge during various water management periods. The average thresholds of drainage discharge, at which N export from paddy fields equalled to zero, were 45.2 m³ day-1 ha-1 for NH4+--N,51.9 m³ day-1 ha-1 for NO3---N, and 55.5 m³ day-1 ha-1 for TN. These findings indicate that controlling drainage discharge is important for the reduction of water loss and N loss from paddy fields. [ABSTRACT FROM AUTHOR]

The risk analysis of an irrigation water allocation strategy based on physical mechanisms is critically important in practice. Conventional risk analysis only considers the role of the channel system and ignores the factors related to on-farm ponds. This paper proposes a channel-pond joint water supply mode (CPJM) based on copula approaches. Two copulas, the Plackett copula and No.16 copula, are chosen and two types of analyses are carried out with the proposed mode: (1) a risk assessment of CPJM with joint probability and conditional probability; and (2) determination of the water supply strategy given the pond water supply frequency. With a case study of the second channel in the Zhanghe Irrigation District (ZID), Southern China, nine combinations of channel water supply frequency (CWSF) and pond water supply frequency (PWSF) are studied. The results reveal that the failure probabilities of the joint distribution and the conditional distribution of the CPJM are 0.02%–16.54% and 0.45%–33.08%, respectively, with corresponding return period of 42–5000 and 10–222 years. Nevertheless, a previous study has shown that the real probability is 33.3%, which means that the return period is equals to three years. Therefore, the objective failure evaluation of the irrigation water-use strategy is useful for water saving in this channel system. Moreover, the irrigation water allocation strategy can be determined and the failure charts relating the CWSF and PWSF can be obtained for a predetermined PWSF. Thus, the channel-pond joint water supply mode provides a more reasonable estimate of the irrigation water allocation strategy reliability. [ABSTRACT FROM AUTHOR]

A new method is proposed based on the finite difference method (FDM), differential evolution algorithm and Markov Chain Monte Carlo (MCMC) simulation to identify water quality model parameters of an open channel in a long distance water transfer project. Firstly, this parameter identification problem is considered as a Bayesian estimation problem and the forward numerical model is solved by FDM, and the posterior probability density function of the parameters is deduced. Then these parameters are estimated using a sampling method with differential evolution algorithm and MCMC simulation. Finally this proposed method is compared with FDM-MCMC by a twin experiment. The results show that the proposed method can be used to identify water quality model parameters of an open channel in a long distance water transfer project under different scenarios better with fewer iterations, higher reliability and anti-noise capability compared with FDM-MCMC. Therefore, it provides a new idea and method to solve the traceability problem in sudden water pollution accidents. [ABSTRACT FROM AUTHOR]

In this study, a model for assessing urban water security is developed using an evaluation method of catastrophe theory. To overcome the defects of the traditional catastrophe evaluation method, two aspects of improvement are assessed. One is expanding the scope of application of the traditional catastrophe approach, i.e., new normalization formulae for five lower level indicators contained in the index at the higher level is proposed in theory. The other is solving the problem that the synthetic values are generally high and the differences are not obvious based on the theories of Cramer's Rule and Vander monde determinant. The assessment results in Wuhan city are in good agreement with the actual situation. The comparison between the results of the improved method and a fuzzy comprehensive evaluation method verifies the science and reliability of the developed method. Consequently, it is concluded that the improved method can be an effective tool for assessment of urban water security and provide a valuable reference for improving inadequacies in urban water security. [ABSTRACT FROM AUTHOR]

To evaluate water security, the Water Resources Sustainability Evaluation Model has been developed. The model employs four criteria (economic development, flood control security, water supply security, and water environment security) and has 22 indicators, integrating them using their relative weights. The model is applied to evaluate the water security of Wuhan urban agglomeration, China. The values of the indicators are normalized using the exponential efficacy functions based on the law of diminishing marginal utility. The evaluation results show that, overall, the state of water security in Wuhan urban agglomeration is good, which is in good agreement with the true situation. The comparison between the results of the model and other three evaluation methods by the Spearman coefficient of rank correlation verifies the science and reliability of the developed model. Consequently, it is concluded that the model can be an effective tool for evaluating the states of water security and provide a basis on which to create policies for improving inadequacies in water security. [ABSTRACT FROM AUTHOR]