In recent decades the Jakarta Metropolitan Area has undergone widespread development and led Indonesia's impressive economic growth. But this development and associated urban sprawl has contributed to undesirable water-resource issues, such as pollution, groundwater extraction, and increased flooding. For example, the major floods in 2002, 2007, 2013, and 2014 have caused billions of dollars of direct and indirect economic damage, the destruction of houses and livelihoods, widespread displacement, and loss of life. The Ciliwung River Basin (CRB) has been a major source of flooding in recent years. With an area encompassing 347km2, the CRB starts upstream at Tugu Puncak located between Bogor and Cianjur Regencies, and runs downstream into the Jakarta Bay area. There has been rapid development within the CRB due to the increasing rate of population in Jakarta, Bogor, Tanggerang and Bekasi City. The floods are of both fluvial and coastal origin, and are worsening due to a large number of drivers, including land subsidence, low drainage or storage capacity in Jakarta's rivers and canals, changes to the climate increasing the frequency and severity of extreme weather events. They are also the result of a rapidly growing population, and land use change causing a growth in economic assets located in potentially flood-prone areas. Traditional flood control is focused on structural flood protection measures through physical intervention. Modern flood management also considers prevention and addresses institutional and social aspects. It also extends from upstream to downstream areas to cover the whole river basin. However, the Indonesian context is challenging. Indonesia began a process of rapid government decentralisation in 1999 from a formerly strong centralised government structure. Prior to 1999, the state could enforce flood mitigation measures. Decentralisation has shifted authority to the local level, creating fragmentation among institutions at different levels, and making coordination more complex. This study will consider different aspects of current transboundary river management that could positively or negatively influence the functioning of flood management in the CRB. These will include legal frameworks, roles and responsibility-sharing, modelling, data and information sharing in support of flood forecasting and early warning, dialogue and coordination mechanisms, and stakeholder participation. The project draws upon a range of disciplinary expertise, including hydrological processes, disaster risk reduction, urban planning, public policy, disaster resilience, flood modelling and fluid mechanics, hydraulic engineering, and behavioural science. The team will combine analytical methods (e.g., modelling of key physical flood variables, urban risk flood modelling) with empirical methods that are based on the analysis of observed or potential consequences through the use of interviews, questionnaires and focus groups. The project has the support of and will involve several government institutions at national, regional and local levels in Indonesia. It will also use a community participatory approach that will raise awareness among communities at risk, and also encourage them to hold accountable those actors who are responsible for disaster risk reduction and river basin management. Through these approaches, the results and recommendations from the study will have been co-created, increasing the likelihood of uptake. The fieldwork and model development will deliver a better understanding of how and why the current transboundary river management arrangements are mitigating or exacerbating flood hazard impacts in the CRB. The recommendations will contribute to improved governance and institutional arrangements in the CRB, and can inform improved models for governance of transboundary river basins elsewhere.

The Maritime Continent (MC) is the archipelago of tropical islands that lies between the Indian and Pacific Oceans, with a population of over 400 million. It comprises large (Sumatra, Java, Borneo, and New Guinea) and many smaller islands, with high mountains. High solar input warms the surrounding seas, which supply an abundance of moisture to the atmosphere, turning the whole region into an atmospheric "boiler box". Deep convective clouds rise up over the islands every day, leading to average rainfall rates in excess of 10 mm per day, approximately three times the rainfall rate over the UK. As well as supplying local agriculture, rain that falls over the MC has a far-reaching, global effect on weather and climate. Tremendous heat energy is released by condensation into the atmosphere in these convective clouds. This heat source drives giant, overturning circulations in the atmosphere: the Hadley and Walker cells, which feed into the jet streams and lead to weather and climate changes far downstream, even over the UK. For example, the origins of the infamous cold winter of 1962/63 and the recent very cold March of 2013 have been traced to atmospheric convection over the MC. For these reasons, the MC has been described as the engine room of the global climate system. Due to the complex nature of the distribution of the islands, and fundamental inadequacies in current models of the atmosphere (mainly related to their representation of convection), both climate predictions and weather forecasts show serious errors over the MC, particularly in their simulation of rainfall. Up until now, these errors have been extremely difficult to address, as there has been a lack of suitable observations over this region. Computing power, and the atmospheric modelling expertise to harness the advances in computing resources, has been inadequate to run computer models with sufficient detail to resolve the convective processes and their interactions, which are the building blocks of atmospheric circulation, for long enough to allow interactions with larger scales. However, we now stand on the cusp of transforming our understanding of atmospheric processes over the MC. Computer power and modelling expertise have progressed to the point where we have the capability to run simulations of the atmosphere at sufficient resolution to accurately capture the complex distribution of islands, and to accurately model the convective processes themselves. In response to this, the international Years of the Maritime Continent (YMC) field experiment (2017-2020) will make the measurements of the atmosphere and ocean at the very small scales that are needed to evaluate and understand the outputs of these new model simulations. Through TerraMaris the UK will take a leading role in YMC, by making observations of convective processes over the MC using the UK meteorological research aircraft, atmospheric radars, balloon and land-based measurements on the islands, and observing the surrounding seas using autonomous underwater and surface vehicles. This unprecedented suite of coordinated observations will complement measurements being taken by our international partners. The UK and the TerraMaris research team has led the way in developing high-resolution atmospheric modelling over recent years. We will apply the skills and knowledge learned to understand the complex mechanisms behind the multiple scales of convection and atmospheric circulations that have made the weather over the MC such a tough problem to crack. This knowledge will enable ground-breaking advances in atmospheric modelling, to improve weather forecasts and climate prediction over the MC region, with direct benefit to the substantial regional population. The downstream effects will see these benefits extend to the far corners of the globe, improving global and regional medium-range weather prediction, and climate projections.

Humid heat is a serious risk to human health, reducing the body's ability to cool itself through sweating. The impact on humans will increase under climate change, particularly in tropical and sub-tropical 'hot spots', such as equatorial Africa and the Indian subcontinent, which are highly populated, and already very hot and humid. Whilst there is a growing body of research on dry-bulb temperature extremes, there is very limited understanding of the meteorological drivers of humid heat extremes, particularly the role of moisture transport, rainfall, and evaporation of moisture from the Earth's surface. In the context of humid heat extremes, the ability of weather and climate models to represent these processes and produce accurate weather forecasts and climate projections is largely unquantified. This is despite an urgency to adapt to and mitigate the impacts of globally increasing climate extremes. We will quantify the relative importance of different humid heat drivers on a cascade of scales, from local surface fluxes, to synoptic weather patterns, to the global-scale modes of tropical climate variability. We will map the specific locations (at the village or town scale) that have an increased risk of experiencing the highest maxima in humid heat during more widespread events that affect a larger region, under both current climate and possible future climates. We will quantify a possible emerging compound climate extreme: the co-occurrence of humid heat, heavy rainfall and flooding. The results will provide underpinning knowledge to improve the prediction of humid heat events, informing Early Warning System development and decision making across weather and climate change time-scales.