Land Hydrology Monitoring in North America via GRACE and Hydrology Models: A Comparison Study

English Abstract:

Monitoring the time-varying gravity field with GRACE satellite can be used to derive information about hydrological processes on the Earth surface. In the area of North America, the GRACE signal is contaminated with the effect of glacial isostatic adjustment (GIA). A study has been done to compare hydrological signals from several global hydrology models and determine the one that is closest to the GRACE-observed hydrology signal.

The set of hydrology models investigated consisted of the available releases of the global and regional hydrology models GLDAS 1.0 and NLDAS 2.0. These models use integrated satellite and terrestrial observations along with different data assimilation methods to derive various land surface states and fluxes. The land surface models used for GLDAS 1.0 were the Noah, CLM, Mosaic and VIC, and for NLDAS 2.0 the Noah, Mosaic and VIC. The recent GRACE CSR Release 05 data were also used. Proper masks were applied to cover Greenland and other areas with strong snow growth signal.

The study was focused on the variability of equivalent water height (EWH) which was computed on 1°-grids. To ensure a fair comparison between the GRACE and hydrology EWH fields, the latter were converted to the spherical harmonic domain and filtered with the same filters that were applied to GRACE. The effect of GIA was then removed from GRACE time-series using the latest GIA models.

The computed EWH fields show good agreement with both GRACE signal and seasonality. The models closest to GRACE EWH signal are the GLDAS NOAH and VIC. In North America the GLDAS NOAH is closest to GRACE signal. On the contrary, the GLDAS CLM present the largest disagreements with GRACE signal. The results also show that the GLDAS VIC model exhibits better agreement with GRACE seasonality. Finally, the performance of NLDAS models is similar for both EWH signal and seasonality.