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Understanding each other's models: an introduction and a standard representation of 16 global water models to support intercomparison, improvement, and communication
2021-6-24, Telteu, Camelia-Eliza, Müller Schmied, Hannes, Thiery, Wim, Leng, Guoyong, Burek, Peter, Liu, Xingcai, Boulange, Julien Eric Stanislas, Andersen, Lauren Seaby, Grillakis, Manolis, Gosling, Simon Newland, Satoh, Yusuke, Rakovec, Oldrich, Stacke, Tobias, Chang, Jinfeng, Wanders, Niko, Shah, Harsh Lovekumar, Trautmann, Tim, Mao, Ganquan, Hanasaki, Naota, Koutroulis, Aristeidis, Pokhrel, Yadu, Samaniego, Luis, Wada, Yoshihide, Mishra, Vimal, Liu, Junguo, Döll, Petra, Zhao, Fang, Gädeke, Anne, Rabin, Sam S., Herz, Florian
Global water models (GWMs) simulate the terrestrial water cycle on the global scale and are used to assess the impacts of climate change on freshwater systems. GWMs are developed within different modelling frameworks and consider different underlying hydrological processes, leading to varied model structures. Furthermore, the equations used to describe various processes take different forms and are generally accessible only from within the individual model codes. These factors have hindered a holistic and detailed understanding of how different models operate, yet such an understanding is crucial for explaining the results of model evaluation studies, understanding inter-model differences in their simulations, and identifying areas for future model development. This study provides a comprehensive overview of how 16 state-of-the-art GWMs are designed. We analyse water storage compartments, water flows, and human water use sectors included in models that provide simulations for the Inter-Sectoral Impact Model Intercomparison Project phase 2b (ISIMIP2b). We develop a standard writing style for the model equations to enhance model intercomparison, improvement, and communication. In this study, WaterGAP2 used the highest number of water storage compartments, 11, and CWatM used 10 compartments. Six models used six compartments, while four models (DBH, JULES-W1, Mac-PDM.20, and VIC) used the lowest number, three compartments. WaterGAP2 simulates five human water use sectors, while four models (CLM4.5, CLM5.0, LPJmL, and MPI-HM) simulate only water for the irrigation sector. We conclude that, even though hydrological processes are often based on similar equations for various processes, in the end these equations have been adjusted or models have used different values for specific parameters or specific variables. The similarities and differences found among the models analysed in this study are expected to enable us to reduce the uncertainty in multi-model ensembles, improve existing hydrological processes, and integrate new processes.
Topological data analysis of contagion maps for examining spreading processes on networks
2015, Taylor, Dane, Klimm, Florian, Harrington, Heather A., Kramár, Miroslav, Mischaikow, Konstantin, Porter, Mason A., Mucha, Peter J.
Social and biological contagions are influenced by the spatial embeddedness of networks. Historically, many epidemics spread as a wave across part of the Earth’s surface; however, in modern contagions long-range edges—for example, due to airline transportation or communication media—allow clusters of a contagion to appear in distant locations. Here we study the spread of contagions on networks through a methodology grounded in topological data analysis and nonlinear dimension reduction. We construct ‘contagion maps’ that use multiple contagions on a network to map the nodes as a point cloud. By analysing the topology, geometry and dimensionality of manifold structure in such point clouds, we reveal insights to aid in the modelling, forecast and control of spreading processes. Our approach highlights contagion maps also as a viable tool for inferring low-dimensional structure in networks.
Modular coherent photonic-aided payload receiver for communications satellites
2019, Duarte, Vanessa C., Prata, João G., Ribeiro, Carlos F., Nogueira, Rogério N., Winzer, Georg, Zimmermann, Lars, Walker, Rob, Clements, Stephen, Filipowicz, Marta, Napierała, Marek, Nasiłowski, Tomasz, Crabb, Jonathan, Kechagias, Marios, Stampoulidis, Leontios, Anzalchi, Javad, Drummond, Miguel V.
Ubiquitous satellite communications are in a leading position for bridging the digital divide. Fulfilling such a mission will require satellite services on par with fibre services, both in bandwidth and cost. Achieving such a performance requires a new generation of communications payloads powered by large-scale processors, enabling a dynamic allocation of hundreds of beams with a total capacity beyond 1 Tbit s−1. The fact that the scale of the processor is proportional to the wavelength of its signals has made photonics a key technology for its implementation. However, one last challenge hinders the introduction of photonics: while large-scale processors demand a modular implementation, coherency among signals must be preserved using simple methods. Here, we demonstrate a coherent photonic-aided receiver meeting such demands. This work shows that a modular and coherent photonic-aided payload is feasible, making way to an extensive introduction of photonics in next generation communications satellites.