Soil water variability in the Weatherley grassland catchment, South Africa: II. Soil water content

Abstract

Soil water content is a major factor that affects the hydrological response of a hillslope or catchment. It is therefore important to have reliable soil water content data to estimate catchment water yield. Daily soil water content (θ) data was calculated based on weekly measured and other data for the Weatherley grassland catchment in South Africa. A modelling procedure, based on the soil water balance equation and the interpretation of the physical properties of soils was used to calculate daily θ for all 28 sites for the six-year period. A statistical model performance indicated that the mean index of agreement was 0.88, root mean square error (RMSE) was 6.8 mm water per 300 mm soil and mean unsystematic RMSE to total RMSE was 93%. These results indicated that the calculated soil water contents agreed well with the measured values and could therefore be used with reasonable confidence to fill data gaps. The proposed procedure therefore affords the possibility to increase the resolution of irregular measured soil water content data. This would significantly advance the usability of such data, because the influence of rainfall events on soil water content is frequently missed by manual soil water content measurements.

Soil - water relationships in the Weatherley catchment, South Africa

“…Daily soil water contents were calculated using the procedure described by Van Huyssteen et al (2009b). This included daily soil water contents for two to five, 300 mm layers of 28 soil profiles in the Weatherley catchment, for 6 years from 01 July 1997 to 30 June 2003.…”

Soil water variability in the Weatherley grassland catchment, South Africa: I. Evapotranspiration

“…An accompanying paper (Van Huyssteen et al, 2009) presents the calculation of soil water content of same catchment.…”

“…These values were used in the calculation of daily θ for each layer for the soils in the Weatherley catchment (Van Huyssteen et al, 2009).…”