moisture sm

crop science

actual evapotranspiration

treatment means

pedotransfer functions

root systems

ordinary kriging

estimates soil

terrestrial ecosystem

Journal of Hydrology

• Random Forest (RF) prediction accuracies were slightly higher for interpolation but were similar for extrapolation of root zone soil moisture compared to a process-based model. • Meteorological conditions were found to be less important than land cover and soil hydro-physical groups in estimating root zone soil moisture within a catchment using RF. • Soil properties varying in space and time are needed to improve RF-based extrapolations for extreme dry and wet conditions. Accurate estimates of root zone soil moisture (RZSM) at relevant spatio-temporal scales are essential for many agricultural and hydrological applications. Applications of machine learning (ML) techniques to estimate root zone soil moisture are limited compared to commonly used process-based models based on flow and transport equations in the vadose zone. However, data-driven ML techniques present unique opportunities to develop quantitative models without having assumptions on the processes operating within the system being investigated. In this study, the Random Forest (RF) ensemble learning algorithm, is tested to demonstrate the capabilities and advantages of ML for RZSM estimation. Interpolation and extrapolation of RZSM on a daily timescale was carried out using RF over a small agricultural catchment from 2016 to 2018 using in situ measurements. Results show that RF predictions have slightly higher accuracy for interpolation and similar accuracy for extrapolation in comparison with RZSM simulated from a process-based model combined with data assimilation. RF predictions for extreme wet and dry conditions were, however, less accurate. This was inferred to be due to infrequent sampling of such conditions that led to poor learning in the trained RF model and to incomplete representation of relevant subsurface processes at the study sites in the RF covariates. Since RF does not depend on parameters required to estimate subsurface water flow, it is more advantageous than a process-based model in data-poor regions where soil hydraulic parameter...

Root zone soil moisture estimation with Random Forest