ERA5-Land: soil moisture dry-downs detection over the Argentine Pampas

Abstract. Soil moisture (SM) in the profile is the main reservoir of water available for vegetation. Therefore, monitoring SM during dry-down periods is crucial for understanding vegetation water status, among other applications. Datasets derived from Land Surface Models, such as the ERA5-Land dataset, provide SM estimates at different depths. The aim of this study was to evaluate the ability of ERA5-Land SM data to detect dry-down periods and to test whether its drying time scale aligns with field measurements at three sites in the Argentine Pampas. The analysis was carried out across the three standard soil layers used by ERA5-Land: layer 1 (L1, 0-7 cm), layer 2 (L2, 7-28 cm), and layer 3 (L3, 28-100 cm). First, the evaluation of the ERA5-Land SM data showed a moderate agreement with field data, although it exhibited a high overestimation (bias > |0.09| m3/m3) in the SM estimates. On the other hand, dry-down periods analysis indicated that ERA5-Land SM data was able to detect a similar number of dry-down periods and drying time scales as observed in the field for L1 and L2. In contrast, at L3, both the number of detected periods and the estimated drying time scale were lower. ERA5-Land SM data showed a consistent and expected pattern of faster drying in the shallower layers, demonstrating its potential for monitoring SM dynamics within the profile.