Abstract:
The Gravity Recovery and Climate Experiment (GRACE) mission has provided unprecedented observations of terrestrial water storage (TWS) dynamics at basin to continental scales. TWS is defined as the sum of groundwater, soil moisture, snow, surface water, ice and biomass water. Data assimilation of GRACE TWS observations has been shown to improve simulation of groundwater, streamflow, and snow water equivalent, and has also proven useful for drought monitoring and identifying human impacts on the water cycle. From a modeling perspective, the TWS components are defined as “prognostic hydrological states”. ExistingGRACE data assimilation schemes update these prognostic states directly. In this work, we propose an alternate approach in whichprecipitation fluxes are adjusted in order to achieve the desired change in the hydrological prognostic states. Benefits of such alternative approach comprise (1) the modeled water balance is maintained, as opposed to having to add increments to the water budget components, and (2) the model automatically determines how to distribute the precipitation updates among the TWS prognostic states.We present the feasibility and limitation of this alternative TWS data assimilation approach from a series of synthetic experiments where, by construction, sources of errors and uncertainties are known.