GRACE-FO Data Assimilation Applications and Issues

Multiple projects now assimilate GRACE and GRACE-FO data into land surface models in order to constrain the terrestrial water storage state variables (e.g., groundwater, soil moisture, snow) in those models.  This approach has been employed successfully to generate weekly, global drought and wetness indicators, among other products. However, in some cases GRACE/FO data assimilation can actually degrade the model output due to the spatial and temporal smoothing of localized mass change signals.  We focus on the state of Colorado as an example, where mass changes associated with seasonal snowpack in the mountainous western half of the state become damped by leakage of the weaker mass change signal in the dry eastern half of the state.  The effect is more acute at high elevations where the seasonal snowpack is deepest.  Innovative new GRACE/FO products and/or data assimilation schemes are needed to overcome such issues.