Urban shrubs are one of the main components of urban vegetation and play a significant role in mitigating the urban heat island (UHI) through transpiration. As there are no suitable methods to measure the transpiration rate of urban shrubs, many issues related with urban transpiration rate and UHI are still not properly understood. In this study, the two-dimensional (2D) three-temperature (3T) model is extended to three-dimensional (3D) scale and applied to estimate the transpiration rate of typical urban shrubs from May to December in 2018. Three common species of shrubs are observed in this study, namely Lagerstroemia indica cv “Bush”, Podocarpus macrophyllus var. angustifolius, and Ligustrum vicaryi. Estimated transpiration rates are proofed by isotope method. Results show that (1) the modified 3D-3T model is a reliable method for estimating urban shrub transpiration (R² = 0.61, MAE = 0.10 mm·h⁻¹); (2) urban shrubs have a quite high transpiration rate, ranging from 0.2 to 0.6 mm·h⁻¹ in the daytime; (3) the rate of transpiration varies greatly in different directions of the shrub canopy (top, south, north, east, and west); (4) the 3D-3T model is able to better reflect transpiration characteristics under the heterogeneous condition in urban environments. To the best of our knowledge, the improved 3D-3T model is one of the very few methods that can measuring the transpiration rate of urban shrubs. The results from this study provide meaningful information and a useful tool for measuring urban evapotranspiration and urban planning.

城市灌木是城市植被的主要组成部分之一，在通过蒸腾作用缓解城市热岛（UHI）中起着重要作用。由于没有合适的方法来测量城市灌木的蒸腾速率，因此与城市蒸腾速率和UHI有关的许多问题仍未得到适当的理解。在这项研究中，将二维（2D）三温（3T）模型扩展到了三维（3D）尺度，并用于估算2018年5月至12月典型城市灌木的蒸腾速率。在这项研究中观察到灌木，即紫薇（Lagerstroemia indica cv “ Bush”），罗汉松。狭，而金叶女贞。估计的蒸腾速率通过同位素方法证明。结果表明：（1）改进的3D-3T模型是估算城市灌木蒸腾量的可靠方法（R ²  = 0.61，MAE = 0.10 mm·h ^-1）；（2）城市灌木具有较高的蒸腾速率，范围从0.2到0.6 mm·h ^-1在白天; （3）蒸腾速率在灌木冠层的不同方向（顶，南，北，东和西）变化很大；（4）3D-3T模型能够更好地反映城市环境中非均质条件下的蒸腾特性。据我们所知，改进的3D-3T模型是极少数可以测量城市灌木蒸腾速率的方法之一。这项研究的结果为测量城市蒸散量和城市规划提供了有意义的信息和有用的工具。