The Faidherbia tree (Faidherbia albida) is frequently used as an intercrop in Sahelian agroforestry parklands due to its multi-purpose advantages and reverse phenology. However, its effect upon the water balance remains unclear, due to the challenges in directly measuring water fluxes in the underlying vadose zone. Mechanistic hydrological models can be inversely calibrated on transient observations and used to partition different hydrological components, but the computational burden of the analysis can become impractical if the model itself is computationally expensive. To overcome this limitation, and to provide novel insights into the hydrological role of Faidherbia, we combine a low-fidelity, one-dimensional hydrological model (HYDRUS-1D) with a kriging-based correction function to emulate the response of a high-fidelity, two-dimensional axisymmetric description of the system (HYDRUS-2D). Multiannual measurements of soil moisture and sap flow in a Senegal agroforestry parkland are used in conjunction with Bayesian inference to calibrate the resulting validated multifidelity surrogate, and to inversely estimate soil hydraulic and root water uptake parameters. Results show that the model can reproduce observations with good accuracy and limited uncertainty for both the calibration and the validation phases, and also confirm the phreatophytic behaviour of Faidherbia by indicating the existence of a moderately compensated root water uptake. Moreover, a local sensitivity analysis suggests that a fully compensated uptake could potentially reduce groundwater recharge by 13%. Interestingly, estimated soil hydraulic parameters hint at the possibility of root-induced changes in soil hydraulic properties that mimic preferential and/or macropore flow, resulting in sustained recharge fluxes (≈ 26% of the annual precipitation). The analysis indicates that overall, Faidherbia could have a net positive effect upon the water balance in arid areas.

Faidherbia 树 ( Faidherbia albida) 由于其多用途优势和反物候，经常被用作萨赫勒混农林公园的间作作物。然而，由于直接测量下伏包气带的水通量存在挑战，其对水平衡的影响仍不清楚。机械水文模型可以根据瞬态观测进行逆向校准，并用于划分不同的水文成分，但如果模型本身的计算量很大，则分析的计算负担可能变得不切实际。为了克服这一限制，并提供对 Faidherbia 的水文作用的新见解，我们将低保真度的一维水文模型 (HYDRUS-1D) 与基于克里格的校正函数相结合，以模拟高保真度的响应, 系统的二维轴对称描述 (HYDRUS-2D)。塞内加尔混农林公园土壤水分和液流的多年测量与贝叶斯推理结合使用，以校准由此产生的经过验证的多重保真度替代指标，并逆向估计土壤水力和根系吸水参数。结果表明，该模型可以在校准和验证阶段以良好的准确性和有限的不确定性重现观察结果，并且还通过表明存在适度补偿的根部吸水来确认 Faidherbia 的水生行为。此外，当地敏感性分析表明，完全补偿吸收可能会使地下水补给量减少 13%。有趣的是，估计的土壤水力参数暗示了根系引起的土壤水力特性变化的可能性，这些变化模仿优先和/或大孔隙流，导致持续的补给通量（≈ 26% 的年降水量）。分析表明，总体而言，Faidherbia 可能对干旱地区的水平衡产生净积极影响。