Influence of Eucalyptus globulus plantation growth on water table levels and low flows in a small catchment

► We study the effects of Eucalyptus plantation on water availability during dry period. ► The trees growth causes an increase in the depth of the water table during the summer. ► The rate of fall of the water table has doubled with the development of the trees. ► At the same time the catchment discharge during summer decreased. ► The increase of the transpiration capacity of the growing trees causes these effects. In a catchment with a shallow water table, switching land use from fodder maize and pasture to Eucalyptus globulus plantation altered dry season hydrology: the water table fell more rapidly each year, and the concomitant decrease in discharge soon led to the stream drying up every year. During the first 3 years of growth, the rate of fall of the water table, S, remained stable in spite of rapid stand growth, which is attributed to transpiration in the catchment being dominated by the background vegetation during this period. Between the third and sixth years, S increased linearly with foliage biomass W s (calculated with the 3-PG model as a proxy for the transpiration capacity of the stand). Subsequently, the levelling off of W s as the result of canopy cover reaching 100% was reflected by similar behaviour of S. The final values of S, in the range 4.5–4.9 mm day −1, were just over double the initial values of around 2.2 mm day −1. The influence of plantation with E. globulus on water reserves and discharge needs to be taken into account by catchment management.