Improving the representation of soil moisture by using a semi-analytical infiltration model

Soil moisture is widely recognized as a fundamental variable governing the mass and energy fluxes between the land surface and the atmosphere. In this study, the soil moisture modelling at sub-daily timescale is addressed by using an accurate representation of the infiltration component. For that, the semi-analytical infiltration model proposed by Corradini et al. (1997) has been incorporated into a soil water balance model to simulate the evolution in time of surface and profile soil moisture. The performances of this new soil moisture model [soil water balance module-semi-analytical (SWBM-SA)] are compared with those of a precedent version [SWBM-Green-Ampt (GA)] where the GA approach was employed. Their capability to reproduce in situ soil moisture observations at three sites in Italy, Spain and France is analysed. Hourly observations of quality-checked rainfall, temperature and soil moisture data for a 2-year period are used for testing the modelling approaches. Specifically, different configurations for the calibration and validation of the models are adopted by varying a single parameter, that is, the saturated hydraulic conductivity. Results indicate that both SWBMs are able to reproduce satisfactorily the hourly soil moisture temporal pattern for the three sites with root mean square errors lower than 0.024m(3)/m(3) both in the calibration and validation periods. For all sites, the SWBM-SA model outperforms the SWBM-GA with an average reduction of the root mean square error of similar to 20%. Specifically, the higher improvement is observed for the French site for which in situ observations are measured at 30cm depth, and this is attributed to the capability of the SA infiltration model to simulate the time evolution of the whole soil moisture profile. The reasonable models performance coupled with the need to calibrate only a single parameter makes them useful tools for soil moisture simulation in different regions worldwide, also in scarcely gauged areas. Copyright (c) 2013 John Wiley & Sons, Ltd.