Combining digital soil mapping and hydrological modeling in a data scarce watershed in north-central Portugal

Data scarcity represents a serious limitation to the use of hydrologic models for supporting decision making processes, and may lead to inappropriate measures for integrated water resources management efforts. In particular, the importance of spatially distributed soil information is often overlooked. The forest-dominated Águeda catchment in north-central Portugal is an example of a region with serious soil data availability limitations. The Soil Land Inference Model (SoLIM) approach, combined with information from several soil surveys, was used to create a map of soil properties based upon the effective soil depths of the landscape. The modified soil map provided a better representation of the soil spatial attributes, particularly the distribution of soil water content. The Soil Water Assessment Tool (SWAT) was applied to the Águeda catchment with two input data sets differing in the soil data. Although SWAT performed satisfactorily in simulating daily streamflow for both data sets at the outlet, results of our study indicate that the SoLIM derived soil data set provides a better representation of the first peak flow events after the dry period. Additionally, it is shown that the better representation of profile depth can contribute considerably to the understanding of water balance components at the small scale and for the implications for management. This study underlines the importance of spatially distributed soil information in watershed modeling for decision making in the river basin management process.