Using digital soil hydraulic maps to simulate water balance at the regional scale (southern Portugal) - impact of spatial resolution and modelling approach

Modelling of soil physical, chemical, and biological processes is critical to improve the understanding of soil functions, the effect of agricultural practices on soil degradation, and appropriate soil management strategies. However, the use of such tools at the regional scale is largely limited by the lack of accurate mapping of soil texture and soil hydraulic properties (SHP). To overcome this limitation, SHP digital maps were obtained using two modelling approaches. One used a national harmonized soil texture database and geostatistical simulation to create soil texture maps which were further used as input data to derive SHP maps using local pedotransfer functions (PTFs). The other approach used SHP maps produced by Tóth et al (2017) using soil texture from the product SoilsGrids (Hengl et al, 2017). The SHP maps from both approaches were produced at two spatial resolutions: 250 m and 1000 m. This study aims to evaluate the usefulness of such SHP maps to simulate soil water dynamics and biomass growth at the regional scale using the MOHID-Land model. This model describes the movement of water in the porous medium based on mass and momentum conservation equations that are computed in a 3D grid domain using a finite volume approach. Crop development is simulated using a modified version of the EPIC model. The SHP maps produced using the two modelling approaches and considering two spatial resolutions (250 and 1000 m) were used as inputs for the hydraulic characteristics of soils. Simulations were compared for an irrigation area (Roxo Irrigation District), located in southern Portugal. Results revealed the differences in the components of the soil water balance, with soil inputs from local data being able to better portray landscape heterogeneity.