HIWAVES3 facilitates a dialogue between climate modelers, impact modelers and partners in different geographical regions with knowledge of local societal relevant meteorological events to construct stories of selected high-impact extreme events, simulated for present-day and future climate conditions. The story includes the origin of the extreme event from a meteorological perspective, its inter-regional linkages, its predictability, its societal impact and how climate change affects its magnitude and probability. Such stories, made available for schools, the general public and governments, are effective communication means, more so than bare numbers about the expected mean temperature increase, precipitation changes in percentages and such. Based on surveys, extreme summer events with large societal impacts, like droughts and floods, will be selected from the recent past for China, India and Europe. Similar events will be identified in large ensembles of global climate simulations. The size of the ensembles allows an analysis of the inter-regional linkages between the Arctic, the Midlatitudes and the Indian Monsoon region through large-scale Rossby waves and other meteorological factors leading to the extreme, like soil-moisture and sea-surface temperature conditions. In addition, a one in a thousand year event in China, India and Europe, although not witnessed in the recent past, will be analysed. The predictability of the event, weeks to months in advance will be assessed through additional simulations. Using empirical methods and process-based models, the impact on crop yields and economy will be estimated as well as the number of premature deaths. Using large ensembles under projected 2050 conditions the effect of climate change on these extremes and their impacts will be analysed. This research material is translated into powerful stories about concrete events that illustrate how climate affects man, man affects climate, how different geographical regions are connected and how extreme the weather might get. The meteorological data of these events will be made available for further impact studies.

The Tropical South Pacific (TSP) is a vast area of ocean containing over 5000 small islands supporting a vulnerable human population of c.10 million of which 57% live within 1 km of the coast. All life on these islands depends on reliable precipitation for the provision of freshwater and food security, meaning that changes in the location and intensity of rainfall can result in damaging and costly societal impacts via droughts and flooding, with historical evidence of island abandonment and population migration. Within the TSP, over 10 million people and sensitive ecosystems on the 5700 isolated Pacific islands depend on rainfall from the convective processes generated in the South Pacific Convergence Zone (SPCZ), which is the largest convergence zone in the Southern Hemisphere, and influences regional, hemispheric and global climate, and in turn is influenced by ENSO and other remote modes of climate variability. Movement and strength of SPCZ convergence results in seasonal, interannual and longer term change in precipitation which are linked to severe droughts, cyclone paths resulting in impacts on Pacific island nations ability to meet Sustainable Development Goals, and in the past drove periods of mass human migration. In the last 1000 years, sustained periods of lower rainfall are thought to have contributed to the abandonment of some Atoll islands and the decision to migrate east into the Pacific. In other islands, changes in rainfall led to the development of different styles of agricultural system. However, compared to other parts of the earth, there is comparatively limited information about past precipitation changes in the TSP, in part because of a historical lack of suitable proxies and archives for producing high resolution, continuous records. Proxies for precipitation reconstructed from sediments or stalagmites are limited to marginal areas to the SPCZ and are also short (<600yrs) or have gaps in the timeseries. Current evidence indicates that decadal-centennial changes in SPCZ/TSP precipitation are linked to global modes of remote climate variability, particularly in the Atlantic, the rest of the Pacific, and the Southern Ocean, but our data to test theories or to validate GCMs is relatively short (<100 years). To address the lack of data and to create a step change in our understanding of the processes by which change is generated in the SPCZ by external modes of climate variability we will generate new network of high resolution (10-50yr) quantitative precipitation records from the whole SPCZ region that will capture its movement and change in strength over a 3500 period when we know large changes have occurred. We will utilise new multiproxy syntheses of palaeoclimate records alongside reconstructions of candidate modes of variability such as the Interdecadal Pacific Oscillation (IPO) and Atlantic Multidecadal Variability (AMV) and Southern jet stream index (SAM) to test for their relationship to SPCZ rainfall. Using a global climate/circulation model we will run a suite of experiments using plausible scenarios of modes of climate variability, either in isolation, or combined with each other, and informed by existing and new proxy data. These experiments will allow us to understand the processes by which different modes of climate variability drive SPCZ rainfall, and thus create fundamental new understanding of the decadal-scale SPCZ changes likely under different past and future modes of climate variability. We can achieve this research now due to the timely collaboration between the team currently leading quantitative hydroclimate reconstruction in the SPCZ and Tropical South Pacific (Sear, Sachs, Langdon, Ladd, Croudace), and the team currently leading the mechanistic understanding and modelling of the SPCZ over a range of time scales (seasonal - multidecadal) (Joshi, Matthews, Roberts, Brown, Osborn).

Local and global consequences of climate change (enhanced urban heat islands, worsening environmental conditions) affect most of the world's urban population, but only recently have cities been represented, albeit crudely, in weather forecast models. To manage and develop sustainable, resilient and healthy cities requires improved forecasting and observations that cross neighbourhood-influenced scales which the next generation weather forecast models need to resolve. ASSURE addresses the critical issue of which processes need to be parameterised, and which resolved, to capture urban heterogeneity in space and time. We will advance understanding to develop new approaches and parameterisations for larger-scale urban meteorological and dispersion models by combining the results of field observations, high-resolution numerical simulations and wind tunnel experiments. Field work and modelling will focus on Bristol, as its physical geography provides suitably high levels of complexity and allows whole-city approaches. With mid-sized cities being large sources of greenhouse gases, and where large numbers of people live, it is critical agencies can provide predictions of weather and climate variability across cities of this scale as they need this information to manage and provide their services. ASSURE will include idealised simulations and theoretical analyses to ensure generic applicability. The ASSURE objectives are: * To understand how sources of urban heterogeneity (physical setting, layout of buildings and neighbourhoods, human activities) combine to influence the urban atmosphere in space and time. * To quantify effects of urban heterogeneity at different scales (street to neighbourhood, to city and beyond) on flow, temperature, moisture and air quality controlling processes and to determine how these processes interact. * To develop a theoretical framework that captures key processes and feedbacks with reduced complexity to aid mesoscale and larger model parameterisations. * To inform the development priorities of current weather and climate models that have meso-scale capabilities and are used in decision-making processes (e.g. integrated urban services). The ASSURE high-fidelity simulations and carefully designed experiments will allow us to explore implications of urban heterogeneity in isolated and combined configurations; interpret and integrate field observations (e.g. 3D meteorological and city-scale tracer dispersion experiments); integrate different approaches to understand the magnitude, source, and geographical extent of uncertainties in process models at different scales; synthesize the new knowledge to conduct theoretical analyses; develop algorithms reflecting this analysis. Novel in ASSURE are simulations resolving street to city-scale features that are linked to mesoscale models; field observations capturing vertical and horizontal variations in the urban boundary- and canopy-layers, including novel multi-source gas tracer experiments; and wind tunnel simulations across atmospheric stabilities and model resolution. New insights will be gained on the role of variations in the building morphology (or form), local topography, and human activities (e.g. waste heat, and AQ emissions). ASSURE will produce detailed datasets; in-depth understanding across the scale of atmospheric processes involved; high-fidelity multiscale urban modelling tools; theoretical models taking account of multiscale effects; improved assessment of current meso-scale model skill and the data used by practitioners to explore future urban scenarios as city form and function change. We will work with local and international organisations and companies to ensure the project benefits a broad range of society. They include: Avon Longitudinal Study of Parents and Children, CERC, COWI, ECMWF, Met Office, Delft University of Technology, Stanford University, University Hannover, RWDI, Surrey Sensors and UKCRIC.

The role of external drivers of climate change in mid-latitude weather events, particularly that of human influence on climate, arouses intense scientific, policy and public interest. In February 2014, the UK Prime Minister stated he "suspected a link" between the flooding at the time and anthropogenic climate change, but the scientific community was, and remains, frustratingly unable to provide a more quantitative assessment. Quantifying the role of climate change in extreme weather events has financial significance as well: at present, impact-relevant climate change will be primarily felt through changes in extreme events. While slow-onset processes can exacerbate (or ameliorate) the impact of individual weather events, any change in the probability of occurrence of these events themselves could overwhelm this effect. While this is known to be a problem, very little is known about the magnitude of such changes in occurrence probabilities, an important knowledge gap this project aims to address. The 2015 Paris Agreement of the UNFCCC has given renewed urgency to understanding relatively subtle changes in extreme weather through its call for research into the impacts of a 1.5oC versus 2oC increase in global temperatures, to contribute to an IPCC Special Report in 2018. Few, if any, mid-latitude weather events can be unambiguously attributed to external climate drivers in the sense that these events would not have happened at all without those drivers. Hence any comprehensive assessment of the cost of anthropogenic climate change and different levels of warming in the future must quantify the impact of changing risks of extreme weather, including subtle changes in the risks of relatively 'ordinary' events. The potential, and significance, of human influence on climate affecting the occupancy of the dynamical regimes that give rise to extreme weather in mid-latitudes has long been noted, but only recently have the first tentative reports of an attributable change in regime occupancy begun to emerge. A recent example is the 2014 floods in the Southern UK, which are thought to have occurred not because of individually heavy downpours, but because of a more persistent jet. Quantifying such changes presents a challenge because high atmospheric resolution is required for realistic simulation of the processes that give rise to weather regimes, while large ensembles are required to quantify subtle but potentially important changes in regime occupancy statistics and event frequency. Under this project we propose, for the first time, to apply a well-established large-ensemble methodology that allows explicit simulation of changing event probabilities to a global seasonal-forecast-resolution model. We aim to answer the following question: over Europe, does the dynamical response to human influence on climate, manifest through changing occupancy of circulation regimes and event frequency, exacerbate or counteract the thermodynamic response, which is primarily manifest through increased available moisture and energy in individual events? Our focus is on comparing present-day conditions with the counterfactual "world that might have been" without human influence on climate, and comparing 1.5 degree and 2 degree future scenarios. While higher forcing provides higher signal-to-noise, interpretation is complicated by changing drivers and the potential for a non-linear response. We compensate for a lower signal with unprecedentedly large ensembles. Event attribution has been recognised by the WCRP as a key component of any comprehensive package of climate services. NERC science has been instrumental in its development so far: this project will provide a long-overdue integration of attribution research into the broader agenda of understanding the dynamics of mid-latitude weather.

We propose a network to stimulate new international collaboration in measuring and understanding the surface temperatures of Earth. This will involve experts specialising in different types of measurement of surface temperature, who do not usually meet. Our motivation is the need for better understanding of in situ measurements and satellite observations to quantify surface temperature as it changes from day to day, month to month. Knowing about surface temperature variations matters because these affect ecosystems and human life, and the interactions of the surface and the atmosphere. Surface temperature (ST) is also the main indicator of "global warming". Knowledge of ST for >150 years has been derived from in situ meteorological and oceanographic measurements. These have been fundamental to weather forecasting, to environmental sciences, and to detection and attribution of climate change. Thermal remote sensing of ST from space has a ~30 year history, including operational exploitation. Observations of high accuracy and stability come from the 20-year record of Along Track Scanning Radiometers (ATSRs) . ATSR-class capability will shortly become operational in the space segment of Global Monitoring for Environment and Security (GMES), and will continue until at least 2030. The best insight into ST variability and change through the 21st century will come from jointly using in situ and multi-platform satellite observations. There is a clear need and appetite to improve the interaction of scientists across the in-situ/satellite 'divide' and across all domains of Earth's surface. This will accelerate progress in improving the quality of individual observations and the mutual exploitation of different observing systems over a range of applications. Now is a critical time to initiate this research network. First, the network will link closely to a major new initiative to improve quantification of ST from surface meteorological stations (surfacetemperatures.org). Second, there are areas of acute need to improve understanding of ST: e.g., across regions of Africa, where in situ measurements are very sparse; and across the Arctic, where the evolving seasonal sea ice extent challenges the current practices for quantifying ST variability and change. Third, it is timely to share experience between remote sensing communities. All these motivations are present against a backdrop where ST is, in relation to climate change, of current public interest & relevance to policy. This network will increase the international impact of UK science. UK investigators are involved across the full scope of the proposed ST network, and have leading international roles in several areas. The network will ensure UK participation at the highest level across all domains of ST research. In this proposal, key world-class organisations overseas have roles in steering and/or hosting network activities. The network will welcome participation of others not contacted in preparation of this proposal. Permission will be sought from the originators of all data used for case studies to make the data set freely available. The network will be organised around three themes over three years: Year 1. In situ and satellite ST observations: challenges across Earth's domains Year 2: Quantifying surface temperature across Arctic Year 3: Joint exploitation of in situ and satellite surface temperatures in key land regions. The first theme is an inclusive question, designed to bring together research communities and develop a full picture of common research needs and aspirations. The second theme is a pressing research question to which the network will co-ordinate a useful and unique contribution. The third theme is one of long-term interest and importance in the strengthening of the observational foundations for climate change monitoring and diagnosis.