The proportion of carbon (C) allocated to tree stems is an important determinant of the C sink-strength of global forest ecosystems. Understanding the mechanisms controlling stem growth is essential for parameterization of global vegetation models and to accurately predict future responses of global forest ecosystems in terms of C sequestration. However, due to their underrepresentation in global synthesis we still lack a thorough understanding of intra-annual variations in stem growth of tropical forest ecosystems, which could be especially prone to projected climatic changes. We here present high-resolution data (≤ 6 µm; ≥ 1 min) from a novel monitoring network of wireless devices for automated measurement of expansion and contraction in tree diameter using a membrane potentiometer, point dendrometers on phloem and xylem and sap flow modules to analyze diurnal changes in stem growth. Our results indicate that diurnal changes in stem diameter were associated with sap flow and related to seasonal variations in daytime temperature and water availability, such that daily maximum stem growth was positively related to temperature during the wet season but showed the opposite trend during the onset of the dry season. We show that high-resolution monitoring of wood hydraulics and carbon storage of tropical trees is crucial to determine the response of tropical C storage to intra-annual climate variation and therefore will be key to accurately predict future responses of tropical aboveground carbon storage, and should be of special interest for tropical ecosystem research and earth system science.