Validation of GRACE - derived Terrestrial Water Storage from a regional 1 approach over South America

Validation of GRACE-derived Terrestrial Water Storage from a regional 1 approach over South America 2 Frédéric Frappart (1,2), Lucía Seoane (1), Guillaume Ramillien (1,2) 3 (1) Université de Toulouse, OMP-GET, UM5563, CNRS/IRD/UPS, 14 Avenue Edouard 4 Belin, 31400 Toulouse, France 5 (2) Groupe de Recherche en Géodésie Spatiale 6 7 Abstract : We propose to validate regional solutions consisting of 2° surface tiles of surface 8 mass concentration over South America (90°W-30°W; 60°S-20°N) computed using accurate 9 Level-1 GRACE measurements, by confronting them to other GRACE products (i.e., global 10 GRGS and ICA-400 km GFZ/CSR/JPL combined solutions) and independent in situ river level 11 and discharge datasets. For this purpose, Principal Component Analysis (PCA) was applied to all 12 these types of the GRACE-based solutions to extract the corresponding main orthogonal spatial 13 and temporal modes of variability to be compared for 2003-2010. For the first three spatial 14 modes, regional solutions provide a better geographical localization of hydrological structures, 15 especially indicating major surface and groundwater systems of South America. Over 16 hydrological patterns, records of river level versus time are particularly consistent with the 17 GRACE temporal modes, especially for our regional solutions (i.e., correlations generally greater 18 than 0.7). Interannual variations of GRACE-based Terrestrial Water Storage (TWS) clearly 19 exhibit the signatures of extreme climatic events as the recent droughts and floods that affected 20 South America. Very significant agreement is also found at interannual time-scale between TWS 21 and discharges in drainage basins dominated by the surface reservoir (more than 0.9 of 22 correlation in the Amazon basin). 23