Assessing the use of digital soil maps in hydrological modeling for soil-water budget simulations - implications for water management plans in southern Portugal

Efficient water management plans are required to ensure food security in areas prone to drought and soil degradation. Hydrological modeling can help to achieve this goal by evaluating water availability for different uses, including food production. Fully distributed hydrological models using digital maps of soil properties available for the soil profile are useful for mapping soil-water balance responses, namely water content and water stress. The accuracy of these model responses depends on the quality of the input data, namely, soil hydraulic properties (SHP). Nowadays, we have free access to worldwide digital 1D SHP grids created using global soil datasets, so detailed studies are now needed to evaluate their use in hydrological modeling. We compared the use of a global and a local SHP dataset to simulate soil-water balance at the regional scale in a small irrigation district located in southern Portugal. We explicitly characterized where differences in model responses occur and related those to the variability of soil physical and hydraulic properties, and land use. Our results showed that the choice of the SHP dataset matters. The statistical and spatial variability of simulated water content and water stress for different land uses depended on the dataset used for the numerical simulation. With the global dataset, water content was higher and water stress lower, and both had less statistical and spatial variability compared to the local dataset results. A practical consequence of these findings is misadjusted irrigation schedules, which can be detrimental to crop production and soil quality. A water management plan based on the global results will determine less water requirements, which may not be realistic for the Mediterranean conditions that characterize the study area.