Previous research showed that transpiration in an evergreen broad-leaved forest in northern Thailand (18¿48'N, 98¿54'E) peaked at the end of the dry season. However, rooting depth limitations on soil water use were not investigated. This study examined the impact of rooting depth and soil hydraulic properties on transpiration using a newly developed soil plant air continuum model. The soil texture at the site was classified as silty sand from the measured relationship between the volumetric soil water content and soil water potential at 0.1-m depths. To effectively simulate heat pulse velocity variation corresponding to dry season transpiration and annual discharge, a rooting depth of 4--5 m was needed, assuming a silty sand soil texture under unsaturated conditions. This value is less than the reported maximum rooting depth of trees and is considered reasonable. A penetration test showed that soil became harder at depths of 4--5 m. The model results suggest that a shallower rooting depth is sufficient to maintain the late dry season transpiration peak if other soil textures with lower hydraulic conductivity are assumed. By contrast, the late dry season transpiration peak could not be maintained under unsaturated conditions if a sandy soil texture with high hydraulic conductivity was assumed, even with a rooting depth of 12 m.