Modelling losses of reservoir storage capacity from sedimentation in different landscapes

<p>Reservoir sedimentation represents a significant threat to the reliability of global water and energy supplies. Over the life of a reservoir, storage capacity is gradually lost due to the deposition of sediments. Hydrological models represent a valuable method to study and evaluate the effects of reservoir storage losses on issues such as energy production, discharge capacity, and flood attenuation. The Hydrological Predictions for the Environment (HYPE) model is a semi-distributed, catchment-based hydrology model that has been used to quantify sediment fluxes across a variety of catchment, country, continent, and global modeling domains. In this study, several methods to estimate reservoir storage capacity losses due to sedimentation were added to HYPE, and their impact on sediment simulations and resulting model performance was tested in multiple landscapes in various parts of the world. Selected methods consider the texture and size of deposited sediment particles, the compaction of deposited sediments over time, and the manner in which reservoirs are operated. Results from the study will be used to inform future model development and improve modeling of sediment fluxes at the global scale.</p>

Global modeling of heterogeneous hydroxymethanesulfonate chemistry

Hydroxymethanesulfonate (HMS) has recently been identified as an abundant organosulfur compound in aerosols during winter haze episodes in northern China. It has also been detected in other regions although the concentrations are low. Because of the sparse field measurements, the global significance of HMS and its spatial and seasonal patterns remain unclear. Here, we modify and add to the implementation of HMS chemistry in the GEOS-Chem chemical transport model and conduct multiple global simulations. The model accounts for cloud entrainment and gas–aqueous mass transfer within the rate expressions for heterogeneous sulfur chemistry. Our simulations can generally reproduce quantitative HMS observations from Beijing and show that East Asia has the highest HMS concentration, followed by Europe and North America. The simulated HMS shows a seasonal pattern with higher values in the colder period. Photochemical oxidizing capacity affects the competition of formaldehyde with oxidants (such as ozone and hydrogen peroxide) for sulfur dioxide and is a key factor influencing the seasonality of HMS. The highest average HMS concentration (1–3 µg m−3) and HMS ∕ sulfate molar ratio (0.1–0.2) are found in northern China in winter. The simulations suggest that aqueous clouds act as the major medium for HMS chemistry while aerosol liquid water may play a role if its rate constant for HMS formation is greatly enhanced compared to cloud water.

Development of surrogate models in reliability-based design optimization: A review

<abstract> <p>Reliability-based design optimization (RBDO) is applied to handle the unavoidable uncertainties in engineering applications. To alleviate the huge computational burden in reliability analysis and design optimization, surrogate models are introduced to replace the implicit objective and performance functions. In this paper, the commonly used surrogate modeling methods and surrogate-assisted RBDO methods are reviewed and discussed. First, the existing reliability analysis methods, RBDO methods, commonly used surrogate models in RBDO, sample selection methods and accuracy evaluation methods of surrogate models are summarized and compared. Then the surrogate-assisted RBDO methods are classified into global modeling methods and local modeling methods. A classic two-dimensional RBDO numerical example are used to demonstrate the performance of representative global modeling method (Constraint Boundary Sampling, CBS) and local modeling method (Local Adaptive Sampling, LAS). The advantages and disadvantages of these two kinds of modeling methods are summarized and compared. Finally, summary and prospect of the surrogate–assisted RBDO methods are drown.</p> </abstract>