Estimation of areal soil moisture by use of terrain data

In this study measured soil moisture is related to primary and secondary topographical attributes within two small-scale drainage basins. The study sites are the Buddby and the Dansarhallarna drainage basins within the NOPEX area. The primary topographic attributes slope, aspect, plan and profile curvature, and the secondary topographic attribute, the wetness index, are derived from a 5 m resolution digital elevation model. The relationship with measured soil moisture in the Buddby basin is investigated by linear regression analysis. Based on mean plot measurements for the whole measurement period two different models were established, resulting in a high R-2 value. The best model was achieved with slope, profile curvature and aspect as regression variables. The models obtained were further used to regionalise the results into basin scale at both Buddby and Dansarhallarna. This demonstrated a soil moisture pattern different from the pattern resulting from the wetness index. Finally, models were established, based on two different dates or field campaigns. The results showed a good agreement with the observed soil moisture values, and a higher R-2 value was obtained when using the wetness index for the medium wet period compared to the wettest period. Further analysis is needed to verify the physical significance of the results and their suitability for hydrological modelling.