Abstract for the workshop on Trends in Global Water Cycle Variables, 3-5 November 2004, UNESCO, Paris, France

Trend of continental storage over the half past century The variation of continental storage may have important consequences on water ressources. Its assessments from observations are still insufficient and need more studies. We investigate here its evolution through a 53 year simulation with the ORCHIDEE Land Surface Model. To perform this study, we have built a 53 year forcing data set, named NCC, for land surface models. NCC has a 6-hourly time step from 1948 to 2000 and a spatial resolution of 1x1. It is based on the NCEP/NCAR reanalysis project and a number of independent in-situ observations. We show in this study the adjustments which need to be applied to the reanalysis and how they impact the simulated continental water balance. The forcing data are used to force the ORCHIDEE Land Surface Model. The model outputs are validated with the observed discharges of the world's 10 largest rivers to estimate the combined errors of the forcing data and the land-surface model. The quality of forcing data is improved after each adjustment. The precipitation correction gives the most important improvement in the simulated river discharges while the temperature correction has a significant effect only at high latitudes. The radiation correction improves also the forcing quality, especially in term of discharge amplitude. The trends of terrestrial water storage are studied, globally and regionally. We show that the ORCHIDEE simulations represent well the rupture over some particular regions in the 1970s.