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The risk of surface water flooding (SWF) in England is already high and its frequency and severity is projected to increase in the future. SWF generally occurs due to intense, highly localised rainfall, which is challenging to forecast with sufficient accuracy to take proactive action ahead of flood events. Being able to manage the risk effectively lies in improved rainfall and flood forecast products, better communication of uncertainty and building the capacity of local responders. This study utilises state-of-the-art high-resolution ensemble rainfall forecasts and hydraulic modelling tools alongside a novel post-processing method to develop and trial new SWF forecast products within an incident workshop attended by forecast producers and regional forecast users. Twenty-two of 24 workshop participants reported that the new information would be useful to their organisation but more product development and training in its interpretation is required. Specific recommendations to improve SWF forecast provision include increased support for local government through a single government organisation responsible for SWF, making more use of existing static SWF mapping in a real-time context and employing the process of user-based consultation, as outlined in this study, to guide the future development of future SWF forecast information and processes.

The INCOMPASS field campaign combines airborne and ground measurements of the 2016 Indian monsoon, towards the ultimate goal of better predicting monsoon rainfall. The monsoon supplies the majority of water in South Asia, but forecasting from days to the season ahead is limited by large, rapidly developing errors in model parametrizations. The lack of detailed observations prevents thorough understanding of the monsoon circulation and its interaction with the land surface: a process governed by boundary‐layer and convective‐cloud dynamics. INCOMPASS used the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft for the first project of this scale in India, to accrue almost 100 h of observations in June and July 2016. Flights from Lucknow in the northern plains sampled the dramatic contrast in surface and boundary‐layer structures between dry desert air in the west and the humid environment over the northern Bay of Bengal. These flights were repeated in pre‐monsoon and monsoon conditions. Flights from a second base at Bengaluru in southern India measured atmospheric contrasts from the Arabian Sea, over the Western Ghats mountains, to the rain shadow of southeast India and the south Bay of Bengal. Flight planning was aided by forecasts from bespoke 4 km convection‐permitting limited‐area models at the Met Office and India's NCMRWF. On the ground, INCOMPASS installed eddy‐covariance flux towers on a range of surface types, to provide detailed measurements of surface fluxes and their modulation by diurnal and seasonal cycles. These data will be used to better quantify the impacts of the atmosphere on the land surface, and vice versa. INCOMPASS also installed ground instrumentation supersites at Kanpur and Bhubaneswar. Here we motivate and describe the INCOMPASS field campaign. We use examples from two flights to illustrate contrasts in atmospheric structure, in particular the retreating mid‐level dry intrusion during the monsoon onset.

Deep convective clouds play a key role in tropical weather patterns, summertime rainfall, and the global transport of energy from the tropics to higher latitudes. Current weather and climate models struggle to realistically represent the development and behavior of these clouds. Both the timing of the convection and the role of humidity in the environment are often poorly represented in these models. In this thesis, detailed numerical simulations serve as a virtual laboratory where the influence of the environment on cloud formation is investigated. The evaporation of rain is shown to result in a positive feedback loop that causes the clouds to become wider and deeper. These wider and deeper clouds tend to form at preferential locations. Subsequently, the relative influence of the temperature profile and humidity in the environment is systematically explored. A simple model captures the response of the clouds to these conditions. Flow trajectories are used to investigate the mixing between the clouds and their environment in more detail. These trajectories show that in essence clouds consist of rising air that mixes horizontally with the environment. Finally, we show that the presence of small particulates (aerosols) can delay the formation of precipitation, but nevertheless lead to larger accumulated rainfall., Geoscience and Remote Sensing, Civil Engineering and Geosciences

The rapid transition from shallow to deep convection is investigated using large-eddy simulations. The role of cold pools, which occur due to the evaporation of rainfall, is explored using a series of experiments in which their formation is suppressed.A positive feedback occurs: the presence of cold pools promotes deeper, wider, and more buoyant clouds with higher precipitation rates, which in turn lead to stronger cold pools. To assess the influence of the subcloud layer on the development of deep convection, the coupling between the cloud layer and the subcloud layer is explored using Lagrangian particle trajectories. As shown in previous studies, particles that enter clouds have properties that deviate significantly from the mean state. However, the differences between particles that enter shallow and deep clouds are remarkably small in the subcloud layer, and become larger in the cloud layer, indicating different entrainment rates. The particles that enter the deepest clouds also correspond to the widest cloud bases, which points to the importance of convective organization within the subcloud layer., Geoscience and Remote Sensing, Civil Engineering and Geosciences

This study explores the mechanisms that determine detrainment in deep cumulus convection. A set of 90 high-resolution Large Eddy Simulations is used to systematically explore the sensitivity of continental deep convection to the relative humidity and stability of the free troposphere. It appears that variations in the mass-flux profiles are determined by detrainment, rather than entrainment. The detrainment shows a strong dependence on the critical mixing ratio, a dimensionless parameter which describes which mixtures of cloud core and environmental air are positively buoyant. A conceptual approach to the parameterization of detrainment is proposed on the basis of these results., Geoscience & Remote Sensing, Civil Engineering and Geosciences