This study investigates the hydrologic implications of land use conversion from native vegetation to rubber (Hevea brasiliensis ) in Southeast Asia. The experimental catchment, Nam Ken (69 km^2), is located in Xishuangbanna Prefecture (22°N, 101°E), in the south of Yunnan province, in southwestern China. During 2005 and 2006, we collected hourly records of 2 m deep soil moisture profiles in rubber and three native land‐covers (tea, secondary forest and grassland), and measured surface radiation above the tea and rubber canopies. Observations show that root water uptake of rubber during the dry season is controlled by day‐length, whereas water demand of the native vegetation starts with the arrival of the first monsoon rainfall. The different dynamics of root water uptake in rubber result in distinct depletion of soil moisture in deeper layers. Traditional evapotranspiration and soil moisture models are unable to simulate this specific behaviour. Therefore, a different conceptual model, taking in account vegetation dynamics, is needed to predict hydrologic changes due to land use conversion in the area. Copyright © 2008 John Wiley & Sons, Ltd.