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Description: An analysis of the atmospheric branch of the hydrological cycle by means of a 15 km resolution numerical integration performed using WRF nested in ERA Interim is presented. Two WRF experiments covering the period 2010-2014 were prepared. The first one (N) was configured as in standard numerical downscaling experiments. The second one (D), with the same parameterizations, included a step of 3DVAR data assimilation every six hours. Apart from comparing our results with ERA Interim data, several observational datasets were used to validate the precipitable water (radiosondes and MODIS data), precipitation (EOBS, ECA\&D, TRMM and GPCP) or evaporation (GLEAM). The verification results showed that the D experiment systematically performs better than N and in many instances, too, better than the forcing reanalysis. According to the results, the leading terms of the water balance are the tendency of the precipitable water, the divergence of moisture flux, evaporation and precipitation. No spatial patterns were recognizable for the annual accumulated evaporation, but the effect of the Atlantic fronts was detected in the precipitation patterns. The transboundary moisture fluxes through the contour of the Iberian Peninsula behave differently depending on the season during 2010-2014. During winter, they show a net moisture import through the boundaries. During spring, summer or autumn moisture is exported specially through the Mediterranean coast, and only during midday this feature is reversed due to sea breezes.