Time variations of the regional evapotranspiration rate from Gravity Recovery and Climate Experiment (GRACE) satellite gravimetry

[ 1] Since its launch in March 2002, the Gravity Recovery and Climate Experiment ( GRACE) mission has been measuring the global time variations of the Earth's gravity field with a current resolution of similar to 500 km. Especially over the continents, these measurements represent the integrated land water mass, including surface waters ( lakes, wetlands and rivers), soil moisture, groundwater, and snow cover. In this study, we use the GRACE land water solutions computed by Ramillien et al. (2005a) through an iterative inversion of monthly geoids from April 2002 to May 2004 to estimate time series of basin-scale regional evapotranspiration rate and associated uncertainties. Evapotranspiration is determined by integrating and solving the water mass balance equation, which relates land water storage ( from GRACE), precipitation data ( from the Global Precipitation Climatology Centre), runoff ( from a global land surface model), and evapotranspiration ( the unknown). We further examine the sensibility of the computation when using different model runoff. Evapotranspiration results are compared to outputs of four different global land surface models. The overall satisfactory agreement between GRACE-derived and model-based evapotranspiration prove the ability of GRACE to provide realistic estimates of this parameter.