What question did this study set out to answer?

The aim is to develop a model that accurately predicts soil moisture dynamics from the surface to the root zone.

March 26, 2026Journal of Hydrology0 citationsOpen Access

From near surface to root zone soil water losses: a new model validated with field TDR and remotely sensed data

TMTommaso MartiniPolytechnic University of Turin AOAurora OliveroUniversity of Turin AGAlessio GentilePolytechnic University of Turin

Key Points

The aim is to develop a model that accurately predicts soil moisture dynamics from the surface to the root zone.
Developed the muSEC model based on the surface evaporative capacitor (SEC).
Compared muSEC with three other models of varying complexity.
Utilized multi-year TDR measurements for calibration and validation across different soil types.
Combined in-situ and remotely sensed data to test model performance.
All models accurately reproduced drydowns with RMSE lower than 0.06 cm³ cm⁻³.
MuSEC demonstrated superior depth transferability over other simplified models.
Calibration on surface layers effectively predicted root zone dynamics.

Abstract

Understanding soil moisture drydowns, especially within the root zone, is critical for predicting water availability and crop stress. Remote sensing provides continuous observations of surface soil moisture, but their practical value for agricultural application depends on linking surface dynamics to root zone layers. With this aim, we developed the muSEC model, based on the recently proposed surface evaporative capacitor (SEC). We compared it with three models of increasing complexity: the Laio bucket scheme, a desorptivity-based model, and a Richards solver. The analysis combined multiyear in-situ TDR measurements (depth-averaged soil moisture at 0–15, 0–30, and 0–60 cm) from a sandy grassland with NASA SMAP retrievals from a loamy maize field, thus covering both accurate local root zone monitoring and satellite-scale surface observations, while testing the models across two contrasting soils. Across both sites, all models reproduced drydowns with good accuracy, with a root mean square error consistently lower than a benchmark of 0.06 . Performance systematically improved with depth compared to the surface, in line with expectations for tilled agricultural soils. Calibration on 0–15 cm and validation on 0–60 cm with the in-situ data showed that, under the relatively homogeneous soil conditions considered here, parameters calibrated on surface layers can predict root zone dynamics, an important result for agricultural applications. While model complexity did not automatically translate into superior performance at a single depth, the proposed muSEC showed the best depth transferability among the simplified models, combining structural flexibility with a substantially lighter numerical framework than fully physically based approaches. These results support its potential use for integrating satellite surface soil moisture into agricultural water management, while highlighting the need for further assessment in more heterogeneous soil profiles. • A new multilayer model (muSEC) based on the surface evaporative capacitor (SEC). • Links surface and root zone soil moisture drydown dynamics. • Integrates satellite soil moisture with minimal physical parameters. • Hourly simulations capture daily drydowns across two contrasting soils. • Calibration shows transferability (RMSE 0.06 cm 3 cm -3 ) and physical realism.

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