Addressing the broadest and most pressing issues facing the natural world requires a holistic understanding of the complex interactions that govern it. This requires the use of models - mathematical descriptions of the world - to explain observed trends, answer "what if?" questions and predict future trajectories. As these models evolve to match our increasing understanding of the natural world, so must the research software infrastructure that underpins them. Amongst other things, this software infrastructure is responsible for helping us link models together to assess the bigger picture, promoting trust in scientific results by making model results reproducible, letting us easily use models on the latest high-performance computers, providing a consistent computational environment and access to data to help developers collaborate, and providing interactive visualisations and apps of model results to a broader audience. To use an analogy - just as analytical scientists require access to laboratories full of high-tech equipment to perform scientific experiments, computational scientists require access to virtual laboratories full of the latest software infrastructure to perform computational experiments. Software infrastructure and communities have developed to begin to meet these challenges across the globe, and partners in this project have been leading these developments for several decades. However, these software and communities are currently independent and constrained, either by geography or to particular scientific domains. The goal of this project is to unite this infrastructure around an international community of practice, providing much needed international cohesion across environment modelling software infrastructure. United, this software has the potential to be truly transformative, enabling collaborative innovation where, for example: models can be readily deployed to and dynamically linked within the cloud; physics-based, statistical and data science models can work seamlessly together to provide a step change in how realistically our models predict the natural world, and; results can be shared easily to non-developers via interactive apps. We will showcase this transformative potential through a case study, which will predict the transport of microplastics in the environment from their release, through waterways and the terrestrial environment, out to the ocean. Plastic pollution is widespread and global, with plastic debris present in all parts of the environment, from deep ocean trenches to remote mountains. It poses a potentially significant risk to both the environment and ourselves. Despite this, the modelling of microplastic transport in the environment is in its infancy, and whilst models of individual compartments (rivers, oceans) exist, there are no frameworks capable of predicting high-resolution microplastic transport from source to sea. Our case study will solve this, at the same time as demonstrating the benefits yielded by our united software infrastructure. This infrastructure will underpin the case study, providing the tools needed to link together the hydrological, microplastic transport and coastal ocean models of which it comprises, and providing a collaborative virtual environment to power it. The result will be a modelling framework that not only offers a step change in our ability to predict microplastic transport from source to sea, but that is flexible enough to be adapted to different chemical classes, thereby making a significant contribution to our efforts towards a zero pollution society. We are a new partnership who collectively unites world-leading expertise in software infrastructure development, community building, hydrology, chemical fate modelling and oceanography. All partners are committed to securing a long-term, self-sustaining collaboration that will ultimately help advance environmental modelling far beyond the scope of this project.

This project addresses how environmental change affects the movement of sediment through rivers and into our oceans. Understanding the movement of suspended sediment is important because it is a vector for nutrients and pollutants, and because sediment also creates floodplains and nourishes deltas and beaches, affording resilience to coastal zones. To develop our understanding of sediment flows, we will quantify recent variations (1985-present) in sediment loads for every river on the planet with a width greater than 90 metres. We will also project how these river sediment loads will change into the future. These goals have not previously been possible to achieve because direct measurements of sediment transport through rivers have only ever been made on very few (<10% globally) rivers. We are proposing to avoid this difficulty by using a 35+ years of archive of freely available satellite imagery. Specifically, we will use the cloud-based Google Earth Engine to automatically analyse each satellite image for its surface reflectance, which will enable us to estimate the concentration of sediment suspended near the surface of rivers. In conjunction with other methods that characterise the flow and the mixing of suspended sediment through the water column, these new estimates of surface Suspended Sediment Concentration (SSC) will be used to calculate the total movement of suspended sediment through rivers. We then analyse our new database (which, with a five orders of magnitude gain in spatial resolution relative to the current state-of-the-art, will be unprecedented in its size and global coverage) of suspended sediment transport using novel Machine Learning techniques, within a Bayesian Network framework. This analysis will allow us to link our estimates of sediment transport to their environmental controls (such as climate, geology, damming, terrain), with the scale of the empirical analysis enabling a step-change to be obtained in our understanding of the factors driving sediment movement through the world's rivers. In turn, this will allow us to build a reliable model of sediment movement, which we will apply to provide a comprehensive set of future projections of sediment movement across Earth to the oceans. Such future projections are vital because the Earth's surface is undergoing a phase of unprecedented change (e.g., through climate change, damming, deforestation, urbanisation, etc) that will likely drive large transitions in sediment flux, with major and wide reaching potential impacts on coastal and delta systems and populations. Importantly, we will not just quantify the scale and trajectories of change, but we will also identify how the relative contributions of anthropogenic, climatic and land cover processes drive these shifts into the future. This will allow us to address fundamental science questions relating to the movement of sediment through Earth's rivers to our oceans, such as: 1. What is the total contemporary sediment flux from the continents to the oceans, and how does this total vary spatially and seasonally? 2. What is the relative influence of climate, land use and anthropogenic activities in governing suspended sediment flux and how have these roles changed? 3. How do physiographic characteristics (area, relief, connectivity, etc.) amplify or dampen sediment flux response to external (climate, land use, damming, etc) drivers of change and thus condition the overall response, evolution and trajectory of sediment flux in different parts of the world? 4. To what extent is the flux of sediment driven by extreme runoff generating events (e.g. Tropical Cyclones) versus more common, lower magnitude events? How will projected changes in storm frequency and magnitude affect the world's sediment fluxes in the future? 5. How will the global flux of sediment to the oceans change over the course of the 21st century under a range of plausible future environmental change scenarios?