Validation of GRACE-derived terrestrial water storage from a regional approach over South America

We propose to validate regional solutions consisting of 2° surface tiles of surface mass concentration over South America (90°W-30°W; 60°S-20°N) computed using accurate Level-1 GRACE measurements, by confronting them to other GRACE products (i.e., global GRGS and ICA-400 km GFZ/CSR/JPL combined solutions) and independent in situ river level and discharge datasets. For this purpose, Principal Component Analysis (PCA) was applied to all of these types of GRACE-based solutions to extract the corresponding main orthogonal spatial and temporal modes of variability to be compared for 2003-2010. For the first three spatial modes, regional solutions provide a better geographical localization of hydrological structures, especially indicating major surface and groundwater systems of South America. Over hydrological patterns, records of river level versus time are particularly consistent with the GRACE temporal modes, especially for our regional solutions (i.e., correlations generally greater than 0.7). Interannual variations of GRACE-based Terrestrial Water Storage (TWS) clearly exhibit the signatures of extreme climatic events as the recent droughts and floods that affected South America. Very significant agreement is also found at interannual time-scale between TWS and discharges in drainage basins dominated by the surface reservoir (more than 0.9 of correlation in the Amazon basin).