Numerical Modeling System Research Articles

Enabling high-performance cloud computing for the Community Multiscale Air Quality Model (CMAQ) version 5.3.3: performance evaluation and benefits for the user community.

The Community Multiscale Air Quality Model (CMAQ) is a local- to hemispheric-scale numerical air quality modeling system developed by the U.S. Environmental Protection Agency (USEPA) and supported by the Community Modeling and Analysis System (CMAS) center. CMAQ is used for regulatory purposes by the USEPA program offices and state and local air agencies and is also widely used by the broader global research community to simulate and understand complex air quality processes and for computational environmental fate and transport and climate and health impact studies. Leveraging state-of-the-science cloud computing resources for high-performance computing (HPC) applications, CMAQ is now available as a fully tested, publicly available technology stack (HPC cluster and software stack) for two major cloud service providers (CSPs). Specifically, CMAQ configurations and supporting materials have been developed for use on their HPC clusters, including extensive online documentation, tutorials and guidelines to scale and optimize air quality simulations using their services. These resources allow modelers to rapidly bring together CMAQ, cloud-hosted datasets, and visualization and evaluation tools on ephemeral clusters that can be deployed quickly and reliably worldwide. Described here are considerations in CMAQ version 5.3.3 cloud use and the supported resources for each CSP, presented through a benchmark application suite that was developed as an example of a typical simulation for testing and verifying components of the modeling system. The outcomes of this effort are to provide findings from performing CMAQ simulations on the cloud using popular vendor-provided resources, to enable the user community to adapt this for their own needs, and to identify specific areas of potential optimization with respect to storage and compute architectures.

Atmospheric dynamics and fire-induced phenomena: Insights from a comprehensive analysis of the Sertã wildfire event

The Sertã wildfire started on October 15th, 2017, in a mountainous area in central Portugal, on the hottest day of an exceptionally dry month compared to the previous two decades. This dry spell was attributed to a persistent heatwave from October 1st to 16th, which impacted most of mainland Portugal. Due to the critical weather and vegetation conditions, the fire was very intense, generating a thermal plume that reached high altitudes. The main purpose of this work is to analyze and discuss the impact of the Sertã wildfire on the dynamics of atmospheric mountain circulation. To accomplish this, a numerical modeling system integrating meteorological, fire spread, and smoke dispersion models was employed. The results indicate that the interaction between the wildfire and the local mountain breeze in central Portugal, under the synoptic weather conditions in Europe, which included the Hurricane Ophelia over the Atlantic Ocean and a warm-sector polar frontal depression in northern Europe, led to a locally disturbed weather situation. The consistent, efficient, and uniform local transport of atmospheric properties at lower levels was disrupted, intensifying wind shear and developing more turbulent advection patterns. Moreover, the fire's impact contributed to the development of a baroclinic wave at 500 hPa over mass centers, which settled at the surface and enhanced cloud development over the region. This phenomenon aligns with the atmospheric circulation effects studied in the Bjerknes and Rossby theories.

Evolution of ozone-precursor sensitivity in the Guangdong-Hong Kong-Macao Greater Bay Area of China under the backdrop of climate change

China is facing the dual challenges of worsening ozone (O3) pollution and climate change. Better understanding the cause of O3 pollution and its response to climate change is crucial for developing an effective O3 control strategy in the coming years. In this study, a localized three-dimensional numerical modeling system was applied to investigate the long-term evolution of ozone-precursor sensitivity (OPS) over the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) during September 2030, 2040 and 2050 under different climate scenarios, including four Representative Concentration Pathway (RCP), the Nationally Determined Contribution (NDC), and carbon neutrality (NEU). RCP emissions were corrected both temporally and spatially by bounding with the actual emissions in 2020 to reduce the uncertainty of future emission estimation. The atmospheric oxidative capacity-based HO2/OH indicator was used to quantify the variations of OPS. The percentage of NOx-limited area over the GBA will increase by 9.8%, 14.8% and 16.9% under RCP2.6, RCP4.5 and RCP8.5 in 2050, comparing with those in 2020. NOx-limited area under NEU showed a greater increase by 23.1%, as a result of larger reduction degree of NOx than VOCs. This highlights that deep NOx emission reduction, mostly driven by the structural adjustments in industry, energy, and transportation under the “2060 carbon neutrality” strategy, will accelerate OPS transition into NOx-limited and ensure the gradual improvement of O3 pollution. NOx emission control in some urban areas still in the VOCs-limited OPS in 2050 under NEU, e.g., Guangzhou and Hong Kong, need to be strengthened to speed up O3 mitigation. The findings of this study would improve our understanding on the long-term trends of OPS in the GBA under the backdrop of climate change, and provide guidance for the synergistic reduction of greenhouse gases and air pollutants in the future.

Harbor Sedimentation Management Using Numerical Modeling and Exploratory Data Analysis

Sedimentation in the harbors’ basins is an environmental phenomenon that frequently disrupts safe shipping and necessitates costly dredging operations. The layout of harbors and the permeability of protective structures such as breakwaters influence sediment transport within harbor basins. Thus, through a multistep framework, this study investigates the sedimentation management issues for the Egyptian proposed Ezbet Elborg fishing harbor based on field measurements and a numerical morphodynamic coastal modeling system (CMS). First, field measurements were analyzed and evaluated for acquiring a full grasp of the research area’s bathymetry and hydrodynamics. Second, a two-dimensional (2D) numerical simulation CMS model was set up and calibrated against field measurements wherein the developed CMS model highly correlated with actual measurements by 97%. CMS results demonstrate that the predominant NNW wave with the formed longshore current on both the harbor’s sides affects sediment accumulation within the harbor’s basin. Third, 100 simulations for the proposed harbor including different structural modulation scenarios affecting the sedimentation issue were investigated via the calibrated CMS model. Finally, an exploratory data analysis (EDA) is performed via correlation matrix and ANOVA test for the CMS’s scenarios’ results to gain an in-depth view of the relation between the harbors’ layout and the structural characteristics with the sedimentation volumes. Results showed that breakwaters’ orientation affects sediment accumulation more than its length. Also, breakwater permeability and basin width are significantly affecting sediment accumulation. Ultimately, the current study makes a substantial contribution to integrated coastal structure management (ICSM) by helping coastal stakeholders to mitigate the negative impacts of the harbors’ sediment deposition aiming at sustaining both environmental and economic aspects.

Holocene sedimentary distribution and morphological characteristics reworked by East Asian monsoon dynamics in the Mekong River shelf, South Vietnam

The distribution of Holocene sediments in the Mekong River shelf area was investigated using shallow seismic and core data. The results show that the shelf depositional stratigraphy since the last glacial period can be classified into four depositional units (U1, U2, U3 and U4). The average thickness of the Holocene deposit in the nearshore area of the Mekong River estuary is approximately 20 m and decreases seaward. In addition to a thickened deposit in the palaeo-river channel, two sedimentary centres have developed, namely, the Mekong River estuary and the Cape Ca Mau area. In contrast to nearshore deposition, the Holocene sedimentation rate rapidly decreased offshore, even in the transgressive systems tract. To understand the driving mechanisms for the variation in Holocene deposition, a three-dimensional numerical model and Geographic Information System(GIS)-based model were applied to reconstruct the oceanographic and sediment transport patterns on the South Vietnam shelf. The simulation results reveal that the Mekong River shelf has undergone significant transformations since the Last Glacial Maximum (LGM). During the LGM, the coastline was situated near the shelf break, and as the sea level rose rapidly, the shoreline retreated. When the sea level reached its peak, the modern Mekong Delta emerged. Furthermore, the distribution of Holocene deposits is controlled by monsoon-influenced seasonal variations in currents, resulting in a triangular delta and narrow strip-like subaqueous clinoform. Our simulation results also show obvious erosional capacity in the offshore area, leading to an evident erosional through to the east of Cape Ca Mau and erosion of Pleistocene sediments in the shelf break area. By combining stratigraphic interpretation and oceanographic simulations, our study provides new insights into sediment transport and erosion processes mediated by ocean currents driven by East Asian monsoons.

Development of Decision Support System (DSS) for surface runoff and erosion control structures planning: a case study in the Upper Citarum Watershed & towards sustainability inland waters ecosystem

The watershed ecosystem is a complex system in which there are numerous transportation and transfer mechanisms of mass and energy. To make management more effective in all national critical watersheds, there needs to be more scientific, evidence-based policymaking that is based on an understanding of the system and mechanisms of the socio-hydrological processes of the watershed. The availability of Decision Support System (DSS) technology can be the appropriate approach to this need because DSS can be an interface between scientific and practical needs (easy-to-use, easy-to-access, user-friendly). However, the availability and implementation of DSS as an important tool in the optimal design of sustainable watershed management in Indonesia are still very limited. This study aims to create a prototype DSS that practitioners and policymakers can use to identify priority areas and optimize technical solutions for controlling surface runoff and soil erosion at various scales in the internal watershed. Herein, the spatial-based numerical modeling system and process mechanism; the database and knowledge; and the Graphical User Interface (GUI) are the three main components that have been used as a framework for model-based DSS development. A distributed rainfall-runoff-erosion model (EcoHydro) is the main engine of DSS for spatially quantifying dimensions of hydrological responses, erosion rate, and sediment production according to the user’s specifications and providing design options for control measures of them. The upper Citarum river basin in West Java, which is a critical and first national priority watershed, has been selected as the case study for DSS development and to demonstrate its application. Furthermore, the resulting DSS can later be developed for use in watersheds and other nationally critical lakes.

Transverse variability of residual currents, sediment fluxes, and bed level changes in estuaries with an estuarine dam: Role of estuarine type, dam location, and discharge interval

Estuarine dams are constructed in estuaries for reasons such as freshwater, flood control, and navigation. By changing tidal and river properties, estuarine dams can change the circulation and sediment transport in estuaries. Previous studies have investigated the along-channel changes in flow and sediment transport, however across-channel changes due to an estuarine dam are not well understood. To increase our understanding, this study analyzed an idealized estuary using the COAWST numerical modeling system. Models of strongly stratified, partially mixed, periodically stratified, and well-mixed estuaries were run for one year. Then, the models were subject to the construction of an estuarine dam and run for another year. For each estuarine type, scenarios with an estuarine dam at x = 20, 55, and 90 km from the mouth and freshwater discharge intervals of Δt = 0.5, 3, and 7 days were investigated, and the scenarios were compared. The results indicated that the river-dominated and tide-dominated estuaries behaved differently. In river-dominated estuaries, the residual circulation tended to be inflow in the channel and outflow over the shoals due to the estuarine exchange flow, and the secondary circulation was bottom divergent due to differential advection. The exchange flow and secondary circulation were found to weaken with longer discharge interval. The sediment fluxes in the channel were dominant, and, despite the weaker exchange flow, were found to be greater and directed seaward due to strong dam discharge for long discharge intervals. In tide-dominated estuaries, the residual circulation tended to be inflow over the shoals and outflow in the channel due to the tide-induced circulation, and the secondary flow was bottom convergent due to differential advection resulting from Stokes return flow. As the estuarine dam was located nearer to the mouth, the tide-induced circulation was replaced with exchange flow, and the secondary flow became bottom divergent. The sediment fluxes in the channel were dominant in this case as well, and were determined by tidal asymmetry from the interaction of the tides with the residual current, becoming directed landward as the seaward tide-induced circulation decreased with the estuarine dam near the mouth. With respect to bed level change, gradients in along-channel sediment fluxes were found to contribute most to bed level change near the mouth and estuarine dam, whereas gradients in across-channel sediment fluxes contributed most to deposition on the estuarine shoals. This study demonstrates that estuarine dam location and discharge interval can alter estuarine transverse variability and improves our understanding compared to previous analyses based solely on along-channel processes.

Dynamics of beach scarp formation behind detached breakwaters

Detached (offshore) breakwaters are widely used as beach stabilization measures. However, there is potential for erosion at the openings between detached breakwaters, which may result in the formation of beach scarps. This study evaluated the formation of beach scarps around breakwaters using field surveys and numerical simulations. The evaluation was conducted using a combination of a recent advanced field survey method and a numerical modelling system combining GPV-MSM, SWAN, and XBeach. The unmanned aerial vehicle photogrammetry results revealed the height of the beach scarp generated behind the detached breakwaters to be approximately 3.0 m at Aoyama beach, Niigata coast, Japan, although sand deposition occurred below sea level towards the detached breakwaters. The numerical simulation using the results of the field survey showed that a combination of high waves and increased water level owing to radiation stress between the shoreline and breakwaters resulted in a steeper slope in the beach morphology. Second, avalanching occurred on the beach, leading to the formation of beach scarps. This study showed that detached breakwaters may lead to high water levels, resulting in the generation of beach scarps behind the breakwaters. This study implied that large beach scarps can be generated even when detached breakwaters are constructed.

Multiyear dynamics of the Aral sea desiccation impact on the Southern Priaralie climate

The impact of the Aral Sea desiccation on the climate of the Southern Priaralieis presented as a systemic impact of two processes: water area reduction and wind-driven salt removal from the dried seabed. For quantitative assessment of this impact, a system of numerical mathematical models has been developed, including a model of atmospheric salt transport, a model of the influence of sea area reduction on temperature and humidity fields, and models of the influence of salt aerosol on radiation regime and precipitation formation. The results of separate realisations of these models are presented to clarify the mechanism and degree of influence of water area reduction and salt removal on climatic characteristics. Multiyear spatial and temporal dynamics of the systemic influence of water area reduction and aerosol removal on annual precipitation, air temperature and humidity is presented for decades of the modelling period (1966-2015).

Forecast modelling of vegetable oil spill events at Paranaguá Port, Brazil

The Port of Paranaguá serves as Brazil's primary outlet for soy oil exports, accounting for nearly 70\% of all shipments in 2021. While less common than mineral oil spills, vegetable oil spills can have similarly devastating environmental effects. This risk underscores the need for effective planning and management of activities involving vegetable oil handling in the region. To address this need, this study developed results based on a forecasting setup focused on describing the behaviour of soy oil spills in the estuarine complex of Paranaguá. The system uses the open TELEMAC-MASCARET three-dimensional numerical modelling system to solve oil movement equations, coupling the hydrodynamic module (Telemac-3d) with the oil module (ECOS). The system is automated through computational routines written in Python and the bash command language, enabling users to initiate simulations and generate dispersion maps to track soybean oil in hypothetical spill scenarios. The processing results were satisfactory, demonstrating the potential for this tool to contribute to minimising the impacts of soybean oil spills in the Bay of Paranaguá. This system can support better decision-making in response efforts, reduce environmental damage, and enhance the protection of local ecosystems.

Ocean Color Image Sequences Reveal Diurnal Changes in Water Column Stability Driven by Air–Sea Interactions

The southward propagation of cold-air frontal boundaries into the Gulf of Mexico region initiates a cascade of coupled air–sea processes that manifests along the coastlines as an apparent brightness anomaly in the ocean color signals. Our hypothesis is that the color anomaly is largely due to the turbulent resuspension of sedimentary particles. Initially, there is significant wind-driven ocean turbulence as the frontal boundary passes, followed by the potential for sustained convective instability due to significant heat losses from the ocean surface. These cold front events occur during boreal autumn, winter, and into early spring, and the latter episodes occur in the context of the seasonally recurring thermal stratification of shelf waters. Here, we show that as stratification reasserts thermal stability in the waning days of a cold front episode, daily to hourly ocean color patterns are temporally coherent with the air–sea heat flux changes and the resulting impact on water column stability. Concomitant results from a nested, data-assimilative, and two-way coupled ocean-atmosphere numerical modeling system provides both corroboration and insight into how surface air–sea fluxes and in-water turbulent mixing manifest as hourly changes in apparent surface water turbidity due to the potential excitation and settling of reflective particles. A simple model of particle mixing and settling driven by the simulated turbulence mimics patterns seen in the satellite image sequences. This study offers a preview of potential application areas that may emerge following the launch of a dedicated ocean color geostationary sensor.

Characterization of salt wedge intrusion process in a geographically complex microtidal deltaic estuarine system

Deltas are strategic systems of high ecological and economic importance since they provide various environmental resources and fertile alluvial soils. Different types of hydrodynamic processes occur in deltas, including saline intrusion. We implemented a three-dimensional numerical modeling system using the EFDC + Explorer Modeling System to analyze the characteristics of saline intrusion in the Sinú River delta, Colombia. We configured the model with field data from two measurement campaigns in February and November 2021, dry and wet seasons, respectively, and with secondary information. Several climatic conditions to cover a wide range of variability in the main forcing factors were simulated, specifically river discharge and tides: (1) without the influence of the El Niño Southern Oscillation (ENSO) climatic phenomena; (2) under critically low conditions of flow discharge; and (3) with sea level rise forecasts. The model was calibrated using in-situ water velocity data and salinity profiles. We obtained Index of Agreement (d) values between 0.67 and 0.99 for salinity and higher than 0.9 for water velocity. The numerical simulation provides valuable information about this stratified salt wedge system's dynamic nature, mainly due to changes in river discharge. The simulation demonstrated that river discharges above 319 m3/s were sufficient to prevent salt wedge intrusion, which are typical values registered annually between May and November. The scenarios under critical low discharge conditions and sea level rise projections showed a maximum reach of the salt wedge intrusion of 7.40 km. The model proved efficient in evaluating the saline intrusion process in the Sinú River delta, obtaining practical results that describe the dynamics of this process. It was shown that by simulating physical processes, such as salinity stratification, numerical models provide useful information on how these estuarine systems respond to different environmental stress factors associated with current climate variability, such as long drought periods or El Niño South Oscilation (ENSO), since salinity gradients play an important role in deltas' aquatic life, since they influence the distribution of phytoplankton, which is a key player for primary productivity.

Quantification of error sources in wave runup estimates on two Mediterranean sandy beaches

Projected future sea level rise and marine storminess is a serious threat for beaches as they induce beach flooding and erosion. Among other factors, wave runup play an important role in beach evolution and must be robustly assessed. However, little attention has been paid to the uncertainties associated to its characterization and how do they compare to other sources of uncertainty. We have quantified the impact of several sources of error in the estimation of wave runup on sandy beaches. Understanding what factors are more influential in the accuracy of the results will help to determine the main sources of uncertainty in beach flooding projections. A calibrated state-of-the-art numerical modelling system has been setup for two beaches in the Mallorca islands (NW Mediterranean). The system has been forced with the best available information of nearshore incoming waves and has been validated against observations to define the benchmark accuracy. To determine the key factors affecting the accuracy of the system's results, different systems configurations have been tested with different degrees of complexity.Our results show that using the most sophisticated modelling system with the best information on boundary conditions, bottom bathymetry, and submerged vegetation leads to a swash RMSE comparable to the standard deviation of the observed swash. We have also found that the choice of lateral boundary conditions (i.e., source of information for the incoming waves) can double the RMSE and induce large biases. Our results also show that using a simple empirical approach usually underestimates the wave runup. However, in locations with vegetated seabed there is a compensation error, and the empirical approach can lead to acceptable results if forced by nearshore waves. In addition, we have compared the error estimates obtained with uncertainties associated to projected sea level rise. Our findings suggest that the uncertainty associated with wave runup modelling should be considered in the assessment of the total uncertainty of future beach flooding, since the analysis performed indicates that this uncertainty can account for between 16% and 60% of the uncertainties linked to mean sea level projections.

Hardware-In-the-Loop test for the optimal damping identification of oscillating buoy wave energy converters

The Power-Take-Off (PTO) damping is a significant factor on energy harvesting capacity of Wave Energy Converters (WEC), which cannot be determined through the traditional laboratory test. In order to consider the complexity of the PTO damping mechanism, the Hardware-In-the-Loop (HIL) methodology is employed to focus on the PTO performance and the energy harvesting capacity in this paper. The dynamic numerical model, servo drives, and data transmission system are integrated in the HIL system, and the established system is then applied to the optimal damping identification of the WEC device which is assembled with the PTO containing a Mechanical Motion Rectifier (MMR). The experimental results indicate that the maximum power appears at the different damping values since the multi-stage energy capture characteristics are affected by the damping mechanism within the mechanical PTO, and the wave height has little effect on the damping values corresponding to the maximum power. This phenomenon is worth noting during the process of the PTO test, and could provide intuitive guidance for the reasonable design and control strategy optimization of the PTO.

EFFECTS OF WAVE SKEWNESS AND ASYMMETRY ON THE EVOLUTION OF FIRE ISLAND, NEW YORK

Bedload transport of sediment by waves and currents is one of the key physical processes that affect the evolution of coasts, nearshore areas, and the engineering practices there. Wave skewness and asymmetry, both of which increase as waves shoal, result in a net bedload sediment flux over a wave cycle. The impacts of this mechanism on large-scale coastal and shoreline change are investigated in this study, using field observations and Coupled Ocean Atmosphere Wave Sediment Transport (COAWST), a hydrodynamic process-based numerical modeling system (Warner et al., 2010). The study site is Fire Island, New York, located at the Atlantic Coast of the USA, with a focus on the persistent shoreline shape, at the western half of this 50-km-long barrier island, that has been hypothesized to be linked to the sand deposits at the shoreface.

Uniform hyperbolicity of a class of scattering maps

In recent years fractal Weyl laws and related quantum eigenfunction hypothesis have been studied in a plethora of numerical model systems, called quantum maps. In some models studied there one can easily prove uniform hyperbolicity. Yet, a numerically sound method for computing quantum resonance states, did not exist. To address this challenge, we recently introduced a new class of quantum maps (Mertig and Shudo 2018 Phys. Rev. E 97 042216). For these quantum maps, we showed that, quantum resonance states can numerically be computed using theoretically grounded methods such as complex scaling or weak absorbing potentials (Mertig and Shudo 2018 Phys. Rev. E 97 042216). However, proving uniform hyperbolicty for this class of quantum maps was not straight forward. Going beyond that work this article generalises the class of scattering maps and provides mathematical proofs for their uniform hyperbolicity. In particular, we show that the suggested class of two-dimensional symplectic scattering maps satisfies the topological horseshoe condition and uniform hyperbolicity. In order to prove these properties, we follow the procedure developed in the paper by Devaney and Nitecki (1979 Commun. Math. Phys. 67 137–46). Specifically, uniform hyperbolicity is shown by identifying a proper region in which the non-wandering set satisfies a sufficient condition to have the so-called sector bundle or cone field. Since no quantum map is known where both a proof of uniform hyperbolicity and a methodologically sound method for numerically computing quantum resonance states exist simultaneously, the present result should be valuable to further test fractal Weyl laws and related topics such as chaotic eigenfunction hypothesis.

Displacement-based structural identification using differentiable physics

Infrastructure is at constant risk of failure due to internal or hidden damage resulting from environmental conditions, variability in building materials, and fabrication errors. These risks can be mitigated by structural health monitoring, but it is difficult to monitor the state of the entire structure using discrete measurements. In this study, we propose a scheme for estimating spatially varying elastic modulus fields of a structural element using differentiable physics to support structural health monitoring efforts. Our approach is evaluated on two numerical model systems, a cantilever beam and a simply supported beam, and systematically evaluated for its sensitivity to initialization, boundary conditions, and a wide variety of spatially varying modulus fields. The results demonstrate the effectiveness of this approach in finding structures with matching displacement responses, while also highlighting its limitations in recovering accurate material properties, as is common in with all inverse methods. To address these limitations, we employ regularization techniques including blur filters and Heaviside projection to mitigate degeneracy and recover more complex fields. This work lays the foundation for more informed decision-making in structural health monitoring, with especially close applications to digital image correlation based approaches.

CoastFLOOD: A High-Resolution Model for the Simulation of Coastal Inundation Due to Storm Surges

Storm surges due to severe weather events threaten low-land littoral areas by increasing the risk of seawater inundation of coastal floodplains. In this paper, we present recent developments of a numerical modelling system for coastal inundation induced by sea level elevation due to storm surges enhanced by astronomical tides. The proposed numerical code (CoastFLOOD) performs high-resolution (5 m × 5 m) raster-based, storage-cell modelling of coastal inundation by Manning-type equations in decoupled 2-D formulation at local-scale (20 km × 20 km) lowland littoral floodplains. It is fed either by outputs of either regional-scale storm surge simulations or satellite altimetry data for the sea level anomaly. The presented case studies refer to model applications at 10 selected coastal sites of the Ionian Sea (east-central Mediterranean Sea). The implemented regular Cartesian grids (up to 5 m) are based on Digital Elevation/Surface Models (DEM/DSM) of the Hellenic Cadastre. New updated features of the model are discussed herein concerning the detailed surveying of terrain roughness and bottom friction, the expansion of Dirichlet boundary conditions for coastal currents (besides sea level), and the enhancement of wet/dry cell techniques for flood front propagation over steep water slopes. Verification of the model is performed by comparisons against satellite ocean color observations (Sentinel-2 images) and estimated flooded areas by the Normalized Difference Water Index (NDWI). The qualitative comparisons are acceptable, i.e., the modelled flooded areas contain all wet area estimations by NDWI. CoastFLOOD results are also compared to a simplified, static level, “bathtub” inundation approach with hydraulic connectivity revealing very good agreement (goodness-of-fit > 0.95). Furthermore, we show that proper treatment of bottom roughness referring to realistic Land Cover datasets provides more realistic estimations of the maximum flood extent timeframe.

Numerical Study of the Morphodynamic Response to a Macro-Scaled Sea-Crossing Project in Hangzhou Bay, China

Hangzhou Bay is a world-famous strong tidal estuary with an irregular coastline, unique topography, numerous human activities, and complex hydro-sedimentological environment. The Daishan-Yangshan Sea-Crossing Transport Corridor (DSTC) project is located at the mouth of Hangzhou Bay, which is composed of multiple sea-crossing bridges, an underground tube tunnel, and several man-made islands. The large-scale engineering of DSTC fully connects the cities of Shanghai, Yangshan, Daishan, Zhoushan, and Ningbo. This article discusses the morphodynamic responses due to the construction of the DSTC based on a state-of-art numerical model system from the perspective of its impacts on the hydro-sedimentological environment of Hangzhou Bay, as well as on adjacent projects. This study proved that the variation range of tide level in Hangzhou Bay is mostly within 2 cm after the implementation of the DSTC, while that of the man-made island and piers is only within 6 cm. The tidal prism decrease percentage of Hangzhou Bay is less than 0.5%. It does not significantly change the current field and underwater topography in Hangzhou Bay, except near the man-made islands and the bridge. The effect of the DSTC on surrounding ports and channels is small and limited. That is, the proposed DSTC engineering is feasible from the perspective of morphodynamic responses. The conclusions provide a useful reference for similar large-scale estuary construction projects.

The extreme heat wave of July-August 2021 in the Athens urban area (Greece): Atmospheric and human-biometeorological analysis exploiting ultra-high resolution numerical modeling and the local climate zone framework.

Greece was affected by a prolonged and extreme heat wave (HW) event (July 28-August 05) during the abnormally hot summer of 2021, with the maximum temperature in Athens, the capital of the country, reaching up to 43.9 °C in the city center. This observation corresponds to the second highest maximum temperature recorded since 1900, based on the historical temperature time series of the National Observatory of Athens weather station at Thissio. In the present study, a multi-scale numerical modeling system is used to analyze the urban climate and thermal bioclimate in the Athens urban area (AUA) in the course of the HW event, as well as during 3 days prior to the heat wave and 3 days after the episode. The system consists of the Weather Research and Forecasting model, the advanced urban scheme BEP/BEM (Building Energy Parameterization/Building Energy Model) and the human-biometeorological model RayMan Pro, and incorporates the local climate zone (LCZ) classification scheme. The system's validation results demonstrated a robust modeling set-up, characterized by high capability in capturing the observed magnitude and diurnal variation of the urban meteorological and heat stress conditions. The analysis of two- and three-dimensional fields of near-surface air temperature, humidity and wind unraveled the interplay of geographical factors (surface relief and proximity to the sea), background atmospheric circulations (Etesians and sea breeze) and HW-related synoptic forcing with the AUA's urban form. These interactions had a significant impact on the LCZs heat stress responsiveness, expressed using the modified physiologically equivalent temperature (mPET), between different regions of the study area, as well as at inter- and intra-LCZ level (statistically significant differences at 95 % confidence interval), providing thus, urban design and health-related implications that can be exploited in human thermal discomfort mitigation strategies in AUA.