Humid heat extremes in the Global (sub)Tropics (H2X)

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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.