Resilience analysis of the nexus across water supply, power generation and environmental systems from a stochastic perspective.

Effects of external disturbances such as the population change on dynamics of water supply, power generation and environmental (WPE) systems have seldom been investigated. Following the WPE nexus profiled in the study of Feng et al. (2016), this study incorporated stochasticity of population, water supply and power generation into the modeling of the dynamical system in the Hehuang region of China, and further quantified resilience measures to understand the system's ability to withstand stochastic disturbances. First, the stochastic differential equations were used to improve the simulation of stochasticity in the WPE nexus. Next, the transient probability distribution functions (pdfs) of system variables, obtained by Monte Carlo simulation, were used to describe the evolutionary process of the system. Finally, the stationary pdfs of variables which reflect stable states of the system were derived to calculate four resilience measures. It is shown that: (1) The system approached a stable state after Year 2400 by calculating the L2 norm of the difference between transient and stationary pdfs. (2) The environmental system was identified as the most vulnerable subsystem because of its long convergence time. (3) The water supply system did not change greatly and it would remain stable at its current low level, i.e., water consumption per capita would be less than 80m3. The method adopted in this study is conducive to avoiding risk and the results provide valuable insights for regional management of a WPE nexus.

Biochar effects on soil properties, water movement and irrigation water use efficiency of cultivated land in Qinghai-Tibet Plateau.

Biochar, has recently, been widely used as a potential soil additive to improve the quality of cultivated land. However, the effect of biochar on irrigation water use efficiency (IWUE) remains unclear in the Qinghai-Tibet Plateau (QTP). Therefore, the purpose of this study was to explore the effects of biochar on the soil properties, water infiltration, and irrigation water efficiency of QTP cultivated land. A column experiment with four biochar application levels (0, 3, 6, and 9 kg·m-2 denoted CK, BC1, BC2, and BC3, respectively) was conducted to explore the biochar effect on the soil water infiltration process. The soil bulk density (γ), saturated water content (θs), soil water retention curve (SWRC), specific water capacity C(h), and saturated hydraulic conductivity (Ks) were measured after the trial. The effects of biochar application level, biochar application depth, irrigation water depth, and initial soil moisture on water loss and IWUE were then simulated by HYDRUS-2D. The results showed that biochar slowed the process of soil water infiltration by changing the soil physical properties and hydraulic properties, reducing the water loss by 5%-15.02%, effectively alleviating the waste of irrigation water, and therefore increasing IWUE by 2%-9.43%. Water loss and IWUE were significantly associated with the biochar application depth and level. Additionally, a biochar level of 6 kg·m-2 showed the best effect for ameliorating the QTP's cultivated soil. These results provide a novel approach for reducing water loss and enhancing the irrigation water use efficiency of QTP cultivated soil.