Snow mass change and evapotranspiration in large river basins
G. Ramillien's inversion method is used to separate the liquid water and snow contribution from the geoid data produced by GRACE. Figure 1presents the seasonal amplitude map of cover thickness estimated from GRACE data (Frappart et al., 2005).
Evapotranspiration at the scale of a river basin
GRACE is also being used to determining the mean evapotranspiration (ET) of several major river basins. The evapotranspiration estimate is based on solving the water mass balance equation: dW/dt=P-ET-R, where P = observed precipitations, R = runoff provided either by in situ measurements or global land surface model outputs, dW/dt = the temporal change in water mass as provided by GRACE solutions: ET = the evapotranspiration rate, the unknown quantity. The GRACE results show that evapotranspiration in equatorial basins (Amazon and Congo) is almost constant throughout the year. This differs from basins located in tropical and mid-latitude regions where a clear annual cycle is visible.
Figure 1 : Seasonal amplitude map of snow cover thickness (in mm of equivalent water) from GRACE