Satellite altimetry from TOPEX/Poseidon (T/P) is used to estimate the variation of the global sea level. This signal, once corrected for steric effects, reflects water mass exchange with the atmosphere and land reservoirs (mainly ice caps, soils and snowpack). It can thus be used to test the capacity of general circulations models (GCMs) to estimate change in land water storage. In this study, we compare the land hydrology contribution to global mean sea level variations during the major 1997--1998 El Ni¿o--Southern Oscillation event from two data sets: (1) the results of the Organizing Carbon and Hydrology In Dynamic Ecosystems (ORCHIDEE) land surface scheme, developed at the Institute Pierre Simon Laplace, coupled to the Laboratoire de M¿t¿orologie Dynamique Atmospheric General Circulation Model (LMD AGCM) and (2) the T/P-based estimates. We show that the seasonal variation of the continental water storage is well represented in the model. The drastic amplitude change between the two contrasted years, 1997 and 1998, observed from satellite altimetry, is also simulated. We analyze the role of each component of simulated water fluxes (precipitation, evaporation, and runoff) in determining the range of annual continental water mass variation and its interannual variability. The difference between the two years, 1997 and 1998, is, for an essential part, due to land precipitation in the 20¿N--20¿S domain. This analysis emphasizes the important role of tropical regions in interannual variability of climate.