A hydropedological approach to simulate streamflow and soil water contents with SWAT+

Abstract

Reflecting internal catchment hydrological processes in hydrological models is important for accurate predictions of the impact of climate and land‐use change on water resources. Characterizing these processes is however difficult and expensive due to their dynamic nature and spatio‐temporal variability. Hydropedology is a relatively new discipline focusing on the synergistic integration of hydrology, soil physics and pedology. Hydropedological interpretations of soils and soil distribution can be used to characterize key hydrological processes, especially in areas with no or limited hydrometric measurements. Here we applied a hydropedological approach to reflect flowpaths through detailed routing in SWAT+ for a 157 ha catchment (Weatherley) in South Africa. We compared the hydropedological approach and a standard (no routing) approach against measured streamflow (two weirs) and soil water contents (13 locations). The catchment was treated as ‘ungauged’ and the model was not calibrated against hydrometric measurements in order to determine the direct contribution of hydropedology on modelling efficiency. Streamflow was predicted well without calibration (NSE > 0.8; R2 > 0.82) for both approaches at both weirs. The standard approach yielded slightly better streamflow predictions. The hydropedological approach resulted in considerable improvements in the simulation of soil water contents (R2 increased from 0.40 to 0.49 and PBIAS decreased from 40% to 20%). The routing capacity of SWAT+ as employed in the hydropedological approach reduced the underestimation of wetland water regimes drastically and resulted in a more accurate representation of the dominant hydrological processes in this catchment. We concluded that hydropedology can be a valuable source of ‘soft data’ to reflect internal catchment structure and processes and, potentially, for realistic calibrations in other studies, especially those conducted in areas with limited hydrometric measurements.

Examining the value of hydropedological information on hydrological modeling at different scales in the Sabie catchment, South Africa

“…By combining modern digital soil mapping (DSM) techniques (McBratney et al., 2003) with hydropedological insight (Van Tol et al., 2021), soil scientists can now produce detailed large‐scale hydrological soil datasets for modeling purposes (Julich et al., 2012; Van Tol et al., 2015; Van Zijl et al., 2020; Van Tol & Van Zijl, 2022; Wahren et al., 2016). This practice has also been underpinned by several studies, which have indicated that improved soil information does indeed improve hydrological modeling efficiency (Bossa et al., 2012; Diek et al., 2014; Romanowicz et al., 2005; Smit & Van Tol, 2022).…”

Impacts of Soil Information on Process-Based Hydrological Modelling in the Upper Goukou Catchment, South Africa

“…The argument is that hydrological soil information may serve as an effective "soft data" tool, especially in ungauged basins where streamflow data is absent, to better represent internal hydrological processes within a catchment [34]. The use of "soft data" in hydrological model configuration and calibration has gained traction in recent years [34][35][36][37], where soft data is defined as information that may not necessarily be measured directly but can be related to a hydrological process or processes.…”

The role of hydropedology when aiming for the United Nations Sustainable Development Goals

“…Of particular interest is the pioneering work in South Africa based on modeling the effect of subsurface pedogenic soil horizons on regional flow regimes (Van Tol, 2020; van Tol & van Zijl, 2022; Van Tol et al., 2018; Van Tol et al., 2021). An intriguing example was generated in Oman where soil scientists observed locally vegetated patterns in an otherwise barren sand basin.…”