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Coastal river deltas are susceptible to flooding from pluvial, fluvial, and coastal flood drivers. Compound floods, which result from the co-occurrence of two or more of these drivers, typically exacerbate impacts compared to floods from a single driver. While several global flood models have been developed, these do not account for compound flooding. Local-scale compound flood models provide state-of-the-art analyses but are hard to scale to other regions as these typically are based on local datasets. Hence, there is a need for globally applicable compound flood hazard modeling. We develop, validate, and apply a framework for compound flood hazard modeling that accounts for interactions between all drivers. It consists of the high-resolution 2D hydrodynamic Super-Fast INundation of CoastS (SFINCS) model, which is automatically set up from global datasets and coupled with a global hydrodynamic river routing model and a global surge and tide model. To test the framework, we simulate two historical compound flood events, Tropical Cyclone Idai and Tropical Cyclone Eloise in the Sofala province of Mozambique, and compare the simulated flood extents to satellite-derived extents on multiple days for both events. Compared to the global CaMa-Flood model, the globally applicable model generally performs better in terms of the critical success index (−0.01–0.09) and hit rate (0.11–0.22) but worse in terms of the false-alarm ratio (0.04–0.14). Furthermore, the simulated flood depth maps are more realistic due to better floodplain connectivity and provide a more comprehensive picture as direct coastal flooding and pluvial flooding are simulated. Using the new framework, we determine the dominant flood drivers and transition zones between flood drivers. These vary significantly between both events because of differences in the magnitude of and time lag between the flood drivers. We argue that a wide range of plausible events should be investigated to obtain a robust understanding of compound flood interactions, which is important to understand for flood adaptation, preparedness, and response. As the model setup and coupling is automated, reproducible, and globally applicable, the presented framework is a promising step forward towards large-scale compound flood hazard modeling.

Coastal river deltas are susceptible to flooding from pluvial, fluvial, and coastal flood drivers. Compound floods, which result from the co-occurrence of two or more of these drivers, typically exacerbate impacts compared to floods from a single driver. While several global flood models have been developed, these do not account for compound flooding. Local scale compound flood models provide state-of-the-art analyses but are hard to scale up as these typically are based on local datasets. Hence, there is a need for globally-applicable compound flood hazard modeling. We develop, validate and apply a framework for compound flood hazard modeling, which consists of the local high-resolution 2D hydrodynamic flood model SFINCS, which is automatically set up from global datasets and loosely coupled with a global hydrodynamic river routing and flood model, as well as a global surge and tide model to account for interactions between all drivers. To test the framework, we simulate two historical compound flood events, cyclones Idai and Eloise, in the Sofala province of Mozambique, and compare the flood extent to observations from remote sensing and to the global quasi 2D CaMa-Flood model. The results show that while the global and local model have similar skill in terms of the critical success index, they result in rather different flood maps. On the one hand, the local model has a higher hit ratio due to the representation of direct coastal and pluvial flooding (rain on grid) and a higher floodplain connectivity. It also shows a faster response to coastal drivers within the estuaries and more realistic flood depth maps. On the other hand, the local model has a higher false alarm ratio, which is partly explained by the inclusion of direct pluvial flooding without sufficient representation of small scale (subgrid) drainage capacity. To showcase a possible application of the framework, we also determine the dominant flood drivers and transition zones between flood drivers for both events. These vary significantly between both events because of differences in the magnitude of and time lag between the flood drivers. We argue that a wide range of plausible events should be investigated to get a robust understanding of compound flood interactions, which is important to understand for flood adaptation, preparedness, and response. As the model setup and coupling is automated, reproducible, and globally applicable, the presented framework is a promising step forward towards large scale compound flood hazard modeling.

Fluvial flood events are a major threat to people and infrastructure. To compute flood risk estimates, modelling cascades are often applied. Therein, flood hazard is driven by hydrologic or river routing and floodplain flow processes. As such, model selection within such a cascade can determine how well some of these processes can be simulated. Depending on the selection made, obtained flood maps can vary and, in turn, can have major implications for the analysis of how many people, buildings, economic values and so forth is at risk. Understanding the role of model selection in the flood risk modelling process is thus of great importance.By means of GLOFRIM 2.0, we coupled the global hydrologic model PCR-GLOBWB with the hydrodynamic models CaMa-Flood and LISFLOOD-FP for the delta region of the Ganges-Brahmaputra basin. Applying the model-coupling framework GLOFRIM facilitates forcing various models with identical boundary conditions and thus transparent and objective inter-comparison of flood models.While replacing the kinematic wave approximation of the hydrologic model with the local inertia equation of hydrodynamic models does not yield better discharge estimates in the Ganges basin, flood maps obtained with LISFLOOD-FP improved representation of observed flood extent. Compared to downscaled products of PCR-GLOBWB and CaMa-Flood, the critical success index increases by around 50 %.Combining the obtained flood maps with actual exposure maps gives then a first-order estimate how the selection for one specific model set-ups translates into varying flood risk estimates. The research thus shows how those model selections, deliberately made or not, are an important driver of simulated flood risk. As such, it is detrimental that the various specifics of a model are known to facilitate the optimal model selection for objective-specific modelling requirements.

Current global riverine flood risk studies assume a constant mean sea level boundary. In reality, high sea levels can propagate up a river leading to elevated water levels, and/or the drainage of high river discharge can be impeded by elevated sea levels. Riverine flood risk in deltas might therefore be underestimated if dynamic sea levels are ignored. This contribution presents the first global scale assessment of drivers of riverine flooding in deltas and underlines the importance of including dynamic downstream sea level boundaries in global riverine flood risk studies.The assessment is based on extreme water levels at 3433 river mouth locations as modeled by the state-of-the-art global river routing model CaMa-Flood, forced with a multi-model runoff ensemble from the EartH2Observe project and bounded by dynamic sea level conditions from the global tide and surge model GTSM. Using this framework, we classified the drivers of riverine flooding at each location into four classes: surge dominant, discharge dominant, compound or insignificant. The classification is based on rank correlations between annual maximum riverine water levels and surge levels, and annual maximum riverine water levels and discharge. We developed a model experiment to quantify the effect of surge on flood levels and impacts.We find that drivers of riverine flooding are compound at 19.7 % of the locations analyzed, discharge dominant at 69.2 % and surge dominant at 7.8 %. Compared to locations with either surge or discharge dominant flood drivers, locations with compound flood drivers generally have larger surge extremes, are located in basins with faster discharge response and/or flat topography. Globally, surge exacerbates 1-in-10 years flood levels at 64.0 % of the locations analyzed, with a mean increase of 13.5 cm. While this increase is the largest at locations with compound or surge dominant flood drivers, surge also affects flood levels at locations with discharge dominant flood drivers. A small decrease in 1-in-10 years flood levels is observed at 12.2 % of locations analyzed due to negative seasonal component of surge associated with dominant seasonal gyre circulations. Finally, we show that if surge is ignored, flood depths are underestimated for 38.2 million out of a total of 332.0 million (11.6 %) expected annual mean people exposed to riverine flooding.

Water-related disasters, such as fluvial floods and cyclonic storm surges, are a major concern in the world's mega-delta regions. Furthermore, the simultaneous occurrence of extreme discharges from rivers and storm surges could exacerbate flood risk, compared to when they occur separately. Hence, it is of great importance to assess the compound risks of fluvial and coastal floods at a large scale, including mega-deltas. However, most studies on compound fluvial and coastal flooding have been limited to relatively small scales, and global-scale or large-scale studies have not yet addressed both of them. The objectives of this study are twofold: to develop a global coupled river-coast flood model; and to conduct a simulation of compound fluvial flooding and storm surges in Asian mega-delta regions. A state-of-the-art global river routing model was modified to represent the influence of dynamic sea surface levels on river discharges and water levels. We conducted the experiments by coupling a river model with a global tide and surge reanalysis data set. Results show that water levels in deltas and estuaries are greatly affected by the interaction between river discharge, ocean tides and storm surges. The effects of storm surges on fluvial flooding are further examined from a regional perspective, focusing on the case of Cyclone Sidr in the Ganges-Brahmaputra-Meghna Delta in 2007. Modeled results demonstrate that a >3 m storm surge propagated more than 200 km inland along rivers. We show that the performance of global river routing models can be improved by including sea level dynamics.

Fluvial flood events were, are, and will remain a major threat to people and infrastructure. Typically, flood hazard is driven by hydrologic or river routing and floodplain flow processes. Since they are often simulated by different models, coupling these models may be a viable way to increase the physicality of simulated inundation estimates. To facilitate coupling different models and integrating across flood hazard processes, we here present GLOFRIM 2.0, a globally applicable framework for integrated hydrologic-hydrodynamic modelling. We then tested the hypothesis that smart model coupling can advance inundation modelling in the Amazon and Ganges basins. By means of GLOFRIM, we coupled the global hydrologic model PCR-GLOBWB with the hydrodynamic models CaMa-Flood and LISFLOOD-FP. Results show that replacing the kinematic wave approximation of the hydrologic model with the local inertia equation of CaMa-Flood greatly enhances accuracy of peak discharge simulations as expressed by an increase of NSE from 0.48 to 0.71. Flood maps obtained with LISFLOOD-FP improved representation of observed flood extent (critical success index C = 0.46), compared to downscaled products of PCR-GLOBWB and CaMa-Flood (C = 0.30 and C = 0.25, respectively). Results confirm that model coupling can indeed be a viable way forward towards more integrated flood simulations. However, results also suggest that the accuracy of coupled models still largely depends on the model forcing. Hence, further efforts must be undertaken to improve the magnitude and timing of simulated runoff. Besides, flood risk is, particularly in delta areas, driven by coastal processes. A more holistic representation of flood processes in delta areas, for example by incorporating a tide and surge model, must therefore be a next development step of GLOFRIM, making even more physically-robust estimates possible for adequate flood risk management practices.

We have developed a low-loss compact superconducting phase shifter for X-band applications. By cascading a discrete variable phase shifter and a continuous variable phase shifter, a total phase shift of 360 degrees was obtained. Both the discrete and variable phase shifter consist of an asymmetrical branch-line coupler, 2 impedance transformers, 2 to 4 varactor diodes and a DC bias feeder. By controlling the bias voltage of the varactor diodes, the asymmetrical branch-line couplers exhibit a nonlinear phase response. As a result, the impedance transformers located between the varactor diodes and the branch-line coupler can be made small, which ensured a compact design. Simulation predicted an insertion loss of less than 1.0 dB and a maximum phase shift of 360 degrees or more. To verify the performance, the proposed superconducting phase shifter was fabricated using a high-Tc superconducting material called YBCO. Measurements performed at X-band show an insertion loss of less than 1.7 dB and a layout size of $0.75\lambda_{g}\times\lambda_{g}$, which confirms the design procedure of a low- loss compact X-band phase shifter.

We have developed an X-band low noise figure (NF) T/R switch-module using a superconducting T/R switch. The superconducting T/R switch was realized by combining a six-port network, two impedance transformers and two varactor diodes. The six-port network consists of one λ/4 transmission line, two λ/2 transmission lines and one 3λ/4 transmission line. For each λ/2 transmission line, a single varactor diode was connected to the center of a given λ/2 transmission line by using one of the aforementioned impedance transformers. The superconducting T/R switch was fabricated using a high- Tc superconducting material called YBCO. An insertion loss of 0.3 dB was measured in Rx mode. By combining the superconducting T/R switch with a limiter and a low noise amplifier (LNA), a low NF T/R switch-module was designed. Measurements performed at X-band show an NF of 0.7 dB, which confirms the design procedure of a low NF T/R switch- module.

We have developed a compact superconducting sub-array module for an X-band phased array antenna. We assume this sub-array module will be applied as a high-sensitivity multichannel T/R module with 16 antenna elements. To realize high-sensitivity, we developed some RF superconducting devices. Using this sub-array module, a high-sensitivity antenna can be easily available for wireless applications such as communication systems and radar systems. In this paper, we describe the newly developed superconducting sub-array module that is applicable as a key component to make an X-band phased array antenna. In particular, RF devices such as a phase shifter, a Tx-Rx switch and a 16-way power divider/combiner were designed as cryogenic circuits by a superconducting technique to acquire low-insertion-loss properties. And by using an internal cooler, noise temperature of Rx channels was reduced to less than 315 K. This sub-array module is 80 mm∗80 mm∗330 mm and small enough to be applied for a large-aperture X-band antenna.

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We report on the improvement brought about by applying a cryogenic receiver to a mobile phone system. The cryogenic receiver consists of a high-Tc superconducting bandpass filter and a cryogenic low-noise amplifier operating at 77 K. Firstly, we measure the RF noisy environment in the horizontal direction in an urban area. The measured result indicated a lower noise characteristic in the cryogenic receiver than in the conventional receiver. As a result, the cryogenic receiver can be expected to improve the signal-to-noise ratio (SNR). Next, we evaluate the communication throughput by using a base station with the cryogenic receiver and demonstrate the superiority of the cryogenic receiver. Throughput improvement in the case of 77 K thermal noise input for the cryogenic receiver was measured to be 6.1 dB compared with the conventional receiver. This result almost agrees with the ideal improvement of SNR by temperature difference. The throughput improvement of the cryogenic receiver by actual radio wave was 1.5 dB to 3.5 dB compared with the conventional receiver at room temperature. This result almost agrees with the improvement of the measured difference of the external environment noise. The cryogenic receiver can be expected to realize high-speed communication.

This paper presents a high-sensitivity high-Tc superconducting (HTS) multi-channel receiver front-end for a 900 MHz band mobile base station. The front-end system has six input/output channels to correspond to a three-sector mobile base station. The front-end modules consist of a thermal insulation transmission line, a small HTS bandpass filter, a cryogenic low-noise amplifier and a high-reliability compact cryocooler. To realize a compact front-end system using a cryocooler, a low-loss thermal insulation transmission line is developed. The thermal insulation transmission line realizes an insertion loss of 0.08 dB and thermal conductivity 1/5 that of conventional thermal insulation semi-rigid coaxial cable. The characteristics of the developed HTS six-channel front-end system operated at 77 K include center frequency of 910 MHz, passband width of 15 MHz, and noise figure of 0.45 dB. The front-end system realized high sensitivity.

The impacts of flooding are expected to rise due to population increases, economic growth and climate change. Hence, understanding the physical and spatiotemporal characteristics of risk drivers (hazard, exposure and vulnerability) is required to develop effective flood mitigation measures. Here, the long-term trend in flood vulnerability was analysed globally, calculated from the ratio of the reported flood loss or damage to the modelled flood exposure using a global river and inundation model. A previous study showed decreasing global flood vulnerability over a shorter period using different disaster data. The long-term analysis demonstrated for the first time that flood vulnerability to economic losses in upper-middle, lower-middle and low-income countries shows an inverted U-shape, as a result of the balance between economic growth and various historical socioeconomic efforts to reduce damage, leading to non-significant upward or downward trends. We also show that the flood-exposed population is affected by historical changes in population distribution, with changes in flood vulnerability of up to 48.9%. Both increasing and decreasing trends in flood vulnerability were observed in different countries, implying that population growth scenarios considering spatial distribution changes could affect flood risk projections.

We have developed an L-band small high-sensitivity microwave receiver module using a superconducting filter. An L-band superconducting filter for a small microwave receiver module is designed as a four-pole elliptic function filter. The resonator uses a stepped-impedance hairpin microstrip line resonator. The developed superconducting filter uses high-Tc superconducting material, YBCO. The fabricated superconducting filter had a low insertion loss of 0.1dB. We have fabricated a small microwave receiver module in which the designed filter is mounted in a cryocooler. The volume of the fabricated module was 2 liters. In addition, the noise figure of the microwave receiver module was 0.5dB. We have demonstrated the receiver module with high sensitivity and small size.

This paper suggests a substrate integrated waveguide in honeycomb structure consisting of a number of small holes (air-filled posts) drilled vertically and entirely through both plating-conductor layers of the substrate (HCSIW), and shows a design method of an SIW right-angle corner as an example of its applications. First, the propagation constant of an HCSIW is derived from the simulation results of a commercial em-simulator (HFSS), and then its effective dielectric constant (e r eff) and transmission loss are discussed. It is shown that the e r eff is approximately determined from the ratio of all the cross-section area of the air-filled posts to the remainder dielectric one, and the transmission loss is comparable with that of a common SIW. Next, the SIW right-angle corner is designed by arranging appropriately honeycomb structure. Experimental verification for the designed right-angle corner is also shown.

This paper proposes a PTFE-filled waveguide cruciform coupler with air-filled posts. Directivity and matched state of the coupler can be realized by “holes” in the dielectric material. The difference of dielectric constant is positively used in designing. First, the design method based on the planar circuit approach is described. Then, the PTFE-filled waveguide cruciform 3dB coupler is designed at Q-Band. Next, the cruciform 3dB coupler is fabricated using the SR (synchrotron radiation) etching process of PTFE, sputter deposition of metal, and electroplating. The measurement results of the fabricated cruciform 3dB coupler are shown.

A metallic waveguide is one of effective media for millimeter- and submillimeter-waves because of the advantage of low-loss. This paper describes trial fabrication of a PTFE-filled waveguide bandpass filter (BPF) with the use of the SR (synchrotron radiation) direct etching process of PTFE, sputter deposition of metal, and electroplating. PTFE is known as a difficult material to process at high precision. However, it has been reported that PTFE microstructures can be fabricated by the direct exposure to SR. In this paper, an iris-coupled waveguide BPF with 5-stage Chebyshev response is designed at Q-band, and the fabrication procedure for the PTFE-filled waveguide BPF is described. The measurement results of the fabricated BPF are shown.