Fluvial and surge-tide extremes can occur synchronously resulting in compound fooding in estuaries, greatly intensifying the hazard. This food risk has the potential to increase in the future as the frequency, phasing and/or intensity of these drivers change. Improved understanding of how extreme fuvial discharge and surge-tides interact will help inform future food mitigation methodology. In this paper, therefore, we resolve for the frst time intra-estuary sensitivities to fuvial and surgetide extremes, for two contrasting UK estuaries (Humber and Dyf). Model simulations at hyper-spatial resolution (<50 m) using a 2D hydrodynamic model predicted compound fooding hazards based on: (1) present-day extreme events (worst on record); (2) present-day extreme events with shifted timings of the drivers to maximise fooding; and (3) modifed drivers representing projected climate change. We found that in a small estuary with short-duration, high-intensity fuvial inputs (Dyf), food extent is sensitive to the relative timing of the fuvial and surge-tide drivers. In contrast, the relative timing of these drivers did not afect fooding in a larger estuary with a slower fuvial response to rainfall (Humber). In the Humber, extreme fuvial inputs during a compound hazard actually reduced maximum water depths in the outer estuary, compared with a surge-tide-only event. Projected future changes in these drivers by 2100 will increase compound fooding hazards: simulated sea-level rise scenarios predicted substantial and widespread fooding in both estuaries. However, projected increases in surge-tide behaved diferently to sea-level rise of the same magnitude, resulting in a greater seawater infux and more fooding. Increased fuvial volumes were the weakest driver of estuarine fooding. In this paper we show how these interactions are complex and how the hydrodynamics vary considerably between diferent estuaries and sites within estuaries, making it difcult to generalise, use probabilistic or use 1D approaches for assessing compound fooding hazards. Hence, we contribute new knowledge and methods for catchment-to-coast impact modelling used for food mitigation strategies.