The added-value of satellite soil moisture observations over irrigated areas to support land surface model developments

In this study, we compared coupled and uncoupled land surface model simulations of surface soil moisture (SM) with passive microwave remote sensing observations of SM over the contiguous US (CONUS). For this purpose, we used the following: (i) the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) satellite retrieved L3 surface SM; (ii) the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) SM derived using LPRM; and (iii) the coupled and uncoupled ORCHIDEE land surface model. The comparison was achieved by computing the temporal mean difference between the normalized remotely-sensed and the model-SM datasets. It was found that both coupled and uncoupled models are drier than the remotely sensed data (particularly the SMOS data) over the principal aquifers of the CONUS. These aquifers are known as one of the places where irrigation is intensive. Therefore, the reason behind this model' dryness could be the fact that the models do not take into account the irrigation activities, which can be monitored by the remotely-sensed observations. Time series of SM over irrigated pixels also showed that SMOS was wetter than the models mainly during the irrigation period.