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

Abstract

Evapotranspiration (ET) is a major component of the soil water balance and therefore requires accurate determination to quantify catchment water yield. Six-year daily ET was determined at 300 mm depth intervals in the root zone of 28 soil profiles in the Weatherley catchment in South Africa. Daily ET was calculated based on the soil water balance equation and interpretation of the physical and morphological properties of the soils. Water losses by ET were studied at various soil water contents. This established the ET/ET₀ for veld grass and therefore enabled the calculation of daily ET from daily ET₀. Resulting annual mean daily ET ranged from 1.4 mm d^{- 1} (50% of rainfall) at the driest hillslope site to 2.6 mm d^{- 1} (90% of rainfall) at the marsh. Results indicated that the proposed procedure enabled fairly accurate determination of ET for the grassland catchment.