Surface soil moisture spatio-temporal dynamics in southeastern South America observed by SMOS and modeled by ORCHIDEE

M. SALVIA; PILES M; POLCHER J; R. RUSCICA; H. KARSZENBAUM; ANNA A. SÖRENSSON

Viena

Workshop; 4th Satellite Soil Moisture Validation and Application Workshop and the CCI Soil Moisture User Workshop; 2017

ESA

SMOS derived τ values showed important sensitivity to the criteria used for defining drydowns:Temporal e-folding decay (τ ) showed no sensitivity to accumulated rainfall above 5 mm, but showed faster drying (smaller τ values) for larger initial SM increases.Different criteria for drydown ending leads to different amount of events (~50% more events in less strict criteria) and to differences of the order of 25% in τ values (larger values with more strict criteria) ORCHIDEE high vertical soil resolution (top 4.5 cm described by 5 layers) makes it suitable for comparison with satellite SM products. However, we have seen that sampling frequency is a crucial issue.Results found in this work where we compared ORCHIDEE and SMOS derived temporal e-folding decay (τ) show differences with previous works that compare SMAP/SMOS with in-situ data:Both SMOS and ORCHIDEE showed smaller τ than Shellito et al 2016 (derived from both SMAP and in situ data) and McColl et al 2017 (SMAP). However, studies are not strictly comparable, since we are working on different areas and seasons (this work: SESA summers, Shellito: USA all year round, McColl: global, all year round). Although it was shown sampling frequency is a strong issue in the comparison between SMOS and ORCHIDEE, the reasons for the important differences found in temporal e-folding decay (τ) need further investigation.The drydown periods offer good perspectives for SM products validation but methodological difficulties still need to be addressed