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Hydrological impacts of climate change upon the Elmley Marshes, southeast England, are simulated using a coupled hydrological/hydraulic model developed using MIKE SHE/MIKE 11 and calibrated to contemporary conditions. Predicted changes in precipitation, temperature, radiation and wind speed from the UK Climate Impacts Programme associated with four emissions scenarios for the 2050s are used to modify precipitation and potential evapotranspiration data. For each emissions scenario two sets of potential evapotranspiration data are derived, one using changes in temperature (PET temp ), the other incorporating changes in temperature, radiation and wind speed (PET trws ). Results indicate drier conditions through the progressively higher emissions scenarios when compared to contemporary conditions. Changes are particularly pronounced when using PET trws . Summer water tables are lower (PET temp 0.01-0.08 m; PET trws 0.07-0.27 m) and the duration of high winter water tables is reduced. Although water tables still intercept the surface in winter when using PET temp , this ceases when PET trws is employed. Summer ditch water levels for the PET temp scenarios are lower (0.01-0.21 m) and in dry winters they do not reach mean field level. Under the PET trws scenarios summer and winter ditch water levels are lower by on average 0.21 m and 0.30 m respectively. Levels never reach the elevation of the marsh surface. Lower groundwater and ditch water levels result in declines in the magnitude and duration of surface inundation which is virtually eliminated with the PET trws scenarios. Hydrological changes can be expected to have ecological impacts which may include the loss of some grassland species adapted to periods of high water table. Reductions in the extent of surface water in spring, especially for the PET trws scenarios, are likely to reduce suitability for wading birds including lapwing (Vanellus vanellus) and redshank (Tringa totanus) for which the marshes are internationally renowned.

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