Evaluation of parameterisation approaches for estimating soil hydraulic parameters with HYDRUS-1D in the groundnut basin of Senegal

Abstract

Soil hydraulic parameters (SHPs) required as inputs for numerical models are scarce in Sahelian regions. Instead, they are estimated using pedotransfer functions (PTFs), but their ability to simulate soil water dynamics has not been evaluated. This study aims to parameterize SHPs with seven different PTFs and inverse modelling to examine their ability to simulate water fluxes in Senegal's Groundnut basin. We used four years of field measurements of soil water content (SWC) and actual evapotranspiration (ET a ) under pearl millet and groundnut crop rotation for model evaluation. Inverse modelling for SWC (root mean square error [RMSE] ≤ 0.015 cm 3 cm −3 ) and ET a (RMSE ≤ 0.62 mm d −1 ) yielded the best model performance compared to PTFs (0.024-0.175 cm 3 cm −3 and 0.68-0.96 mm d −1 , respectively). Where field measurements are lacking for inverse estimation, three of the seven tested PTFs yielded good modelling results and could be used as a parsimonious approach for cultivated Sahelian soils.

Estimating water fluxes in the critical zone using water stable isotope approaches in the Groundnut and Ferlo basins of Senegal

“…For mid-slope locations in open areas (outside tree canopies), the ET a values obtained via validated HYDRUS-1D calculations (Diongue et al, 2022) are on the same order of magnitude as those from isotope mass balances and EC flux values. However, those methods do not predict the same partitioning of E a and T a for those locations, probably due to differences among the models' respective assumptions and partitioning approaches.…”

“…The reason for that discrepancy may be that during the dry season, the water compositions that are used as inputs for the isotope approach reflect the second‐stage evaporation from the soil, while the EC measurements may capture additional fluxes such as transpiration from shrubs and nearby trees. For mid‐slope locations in open areas (outside tree canopies), the ET a values obtained via validated HYDRUS‐1D calculations (Diongue et al, 2022) are on the same order of magnitude as those from isotope mass balances and EC flux values. However, those methods do not predict the same partitioning of E a and T a for those locations, probably due to differences among the models' respective assumptions and partitioning approaches.…”

“…In contrast, the dry season's high ET 0 drives evaporation from surface and soil water, and consequently may induce upward water fluxes from groundwater into the soil. During the year 2021, measured values of rainfall, ET 0 , and actual evapotranspiration ( ET a , from eddy covariance) were 478 mm, 1512 mm, and 453 mm, respectively (Diongue et al, 2022).…”

“…Post-processing of binary files was done with EdiRe (University of Edinburgh, Scotland). Additional details are provided in Diongue et al 2022).…”

“…Rainfall amounts were measured at both sites with a weather station (Campbell TE25MM at Site 1, and Campbell Climavue 50TM at Site 2). Values for the soil-water storage (m i and m f in Equation 4) were derived from the VWC of each soil profile, and ET a was estimated from eddy covariance fluxes at Site 1 (Diongue et al, 2022). For that site, the only unknown variable in the mass balance was the percolation, which was calculated as the residual from the water balance equation (Equation 4).…”