# Presentation: 236788

## Assimilation of GRACE Terrestrial Water Storage Anomalies

**Assimilation of GRACE Terrestrial Water Storage Anomalies**
**Adds Value to the Observation and Improves Model Performance **

- Figure 2: Vertical Disaggregation of GRACE TWS’ into snow, soil water, and groundwater

- Figure 1: Horizontal Downscaling GRACE Terrestrial Water Storage Anomalies (TWS’)

- NASA's GRACE mission has the unique ability to monitor integrated water stored at all depths (i.e., the sum of snow, surface water, soil moisture, and groundwater). However, the space and time resolutions of GRACE observations are coarse.
- By assimilating GRACE observations into a Land Surface Model, we are able to produce estimates of groundwater, soil moisture, and snow variations that combine the veracity of GRACE with the high resolution of the model. This technique will be of particular value for regions that lack reliable data on water availability.

**Ben Zaitchik, Code 614.3, NASA-GSFC and UMCP**

**Hydrospheric and Biospheric Sciences Laboratory**

## Name: Ben Zaitchik (NASA-GSFC and UMCP), Matt Rodell (NASA-GSFC), and Rolf Reichle (NASA-GSFC/UMBC)

**E-mail: **Ben.Zaitchik@nasa.gov
**Phone: **301-286-9147
**References:**
- Zaitchik, B.F., M. Rodell, and R.H. Reichle, 2007: Assimilation of GRACE terrestrial water storage data into a land surface model: results for the Mississippi River basin.  *Conditionally Accepted, Journal of Hydrometeorology*.
- Tapley, B. D., *et al.*, 2004: The gravity recovery and climate experiment: Mission overview and early results. *Geophysical Research Letters*, **31**.
- Koster, R. D., *et al.*, 2000: A catchment-based approach to modeling land surface processes in a general circulation model 1. Model structure. *Journal of Geophysical Research-Atmospheres*, **105**, 24809-24822.
**Data Sources:  **GRACE data used in this study were processed at the University of Texas Center for Space Research (CSR), at the GeoForschungsZentrum Potsdam (GFZ), and at NASA's Jet Propulsion Laboratory (JPL).  Observational groundwater anomalies used in Figure 2 were generated based on unconfined and semi-confined water level records from 58 piezometers distributed across the Mississippi River basin.  Sources included the U.S. Geological Survey (USGS) Ground-Water Climate Response Network (CRN), the USGS WatStore system, the Illinois State Water Survey, and published reports.
- Atmospheric forcing data for model simulations were drawn from the NASA-GSFC GLDAS forcing database (http://ldas.gsfc.nasa.gov). Terrestrial model parameters were drawn from multiple data sources and are described in Koster *et al.* (2000).
**Technical Description of Image:**
***Figure 1:******  ***Terrestrial water storage anomaly (TWS’) for January, 2005, derived from GRACE.  The left panel shows TWS’ estimates based GRACE alone, and the right panel shows TWS’ produced by the assimilation of GRACE into the Catchment Land Surface Model (CLSM) [Koster *et al.*, 2000].  The coarse horizontal resolution of GRACE allows for only one monthly observation for each of the four major sub-basins of the Mississippi.  Assimilation downscales these observations using the high-resolution physics of CLSM and the statistical assimilation tools of the Ensemble Kalman Filter [Zaitchik *et al., *2007].
***Figure 2:***  Groundwater, soil moisture, and snow water equivalent for the Mississippi river basin, as simulated by the Catchment Land Surface Model with assimilated GRACE observations.  Also shown are area averaged daily groundwater observations and monthly GRACE-derived TWS anomalies.  GRACE and modeled TWS are adjusted to a common mean, as are observed and modeled groundwater.
**Scientific significance: **Terrestrial water storage is a variable of large uncertainty in modern Land Surface Models, yet it is of critical importance to terrestrial hydrology, land-atmosphere interactions, and water resources.  The work presented here is the first effort to assimilate GRACE into a Land Surface Model, and it demonstrates the potential of GRACE observations to enhance our understanding of water storage dynamics.
**Relevance for future science and relationship to Decadal Survey: **Terrestrial water storage is a critical component of the global water cycle, yet it is a source of considerable uncertainty in land surface models.  Data assimilation techniques that introduce GRACE observations in uncoupled and coupled land surface models have great potential to improve hydrological predictions and to contribute to future model development.  Applications to drought monitoring and seasonal forecasts are already in development.  The GRACE-II mission, to be launched in the 2016-2020 timeframe, will provide higher precision and higher resolution estimates of TWS, enhancing the scientific and applied potential of the data assimilation technique.

**Hydrospheric and Biospheric Sciences Laboratory**