AbstractConcern has been expressed that Miscanthus x giganteus, a dedicated biomass crop, may have a high water use, with implications for its economic yield and impacts on water resources. There is particular uncertainty about one component of the water use, the interception loss. Measurements of the interception loss were made in a plot of the crop at a site in south‐east England, during 1997/1998 and 1998/1999. The measured interception losses were 25 and 24% of gross rainfall, respectively. Winter interception losses are relatively high, which is attributed to the slow rate of leaf loss. A Monte Carlo procedure was used to optimize three of the parameters of the Gash interception model on the 1997/1998 data. The simulated values had an uncertainty of 1·1 mm per storm in 1997/1998 and 2·9 mm per storm in 1998/1999. The model was also used to investigate the potential effect of the evaporation rate being overestimated due to the measurements being made in an experimental plot. This showed that the interception losses might be reduced to 21 and 18% in field scale plantations. A consideration of the relative interception rate demonstrated that the crop behaved more like a forest, in terms of the interception losses, during the winter months. © Crown Copyright 2010. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.