Spatially and seasonally distributed information on transpiration (T) fluxes is limited in the tropics. Here, we applied a coupled isotope mass balance model to separate water fluxes of T and evapotranspiration (ET) from precipitation (P). The mean annual T was estimated at a resolution of 100 m for Costa Rica (51,100 km²) and a partitioning of monthly T and evaporation (E) for the 2370-km² San Carlos catchment. The dominant flux in the forest ecosystems was T with a mean annual T of 1086 mm that ranged from 700 mm in Tropical Montane Very Humid Forest to 1400 mm in Subtropical and Tropical Low Montane Rainforests. We estimated an average 85% of ET was T, which is concurrent with expectations for forested tropical regions, but varied according to model parameterization and data sources. A model comparison exercise showed a range of mean annual T estimates from 988 to 1465 mm and a range of T/P from 0.35 to 0.5 with temperature and relative humidity exhibiting the highest impact on the model results. Across Costa Rica, we estimated an average loss of precipitation by T of 38% (1085 mm), whereas interception (I) constitutes 10% (230 mm) and direct evaporation (E) only 7% (192 mm). Similarly, the results at the catchment scale indicated that monthly T contributes 76% (85-mm monthly average) to total ET and E corresponds to 24% (24-mm monthly average). The T rates exhibited an opposite seasonality to rainfall with highest T over the drier months from December to April with a peak in March (101–144 mm) and the minimum T in September (53–71 mm). Around 17% (79–130 mm) of precipitation over the catchment area is lost to T, both E (10–35 mm) and I (15–38 mm) correspond to 5%. Despite the inherent uncertainties of the data assumptions and simplifications, including data interpolation errors, the coupled isotope mass balance model showed in comparison to other global products reasonable water partitioning for different ecosystems in Costa Rica and the San Carlos catchment area. These results can help to evaluate the impact of land cover conversion on the hydrological cycle in Costa Rica, and the simple isotope-based model could be transferred to different biomes of the tropics.

中文翻译：

---

热带哥斯达黎加基于同位素的初步蒸散分区方法

在热带地区，蒸腾 (T) 通量的空间和季节性分布信息是有限的。在这里，我们应用耦合同位素质量平衡模型将 T 和蒸散 (ET) 的水通量与降水 (P) 分开。哥斯达黎加 (51,100 km ² )的年平均 T 估计为 100 m 的分辨率，2370 km ²的月 T 和蒸发量 (E) 的划分圣卡洛斯集水区。森林生态系统中的主要通量是 T ，年平均 T 为 1086 毫米，范围从热带山地非常潮湿森林的 700 毫米到亚热带和热带低山地雨林的 1400 毫米。我们估计平均 85% 的 ET 是 T，这与森林热带地区的预期一致，但根据模型参数化和数据来源而有所不同。模型比较练习显示年平均 T 估计值范围为 988 至 1465 毫米，T/P 范围为 0.35 至 0.5，其中温度和相对湿度对模型结果的影响最大。在整个哥斯达黎加，我们估计 T 的平均降水损失为 38%（1085 毫米），而截留 (I) 占 10% (230 毫米)，直接蒸发 (E) 仅 7% (192 毫米)。相似地，流域尺度的结果表明，月 T 对总 ET 贡献了 76%（85 毫米月平均值），E 对应于 24%（24 毫米月平均值）。T 率表现出与降雨量相反的季节性，从 12 月到 4 月的干燥月份 T 最高，3 月达到峰值（101-144 毫米），9 月 T 最低（53-71 毫米）。集水区约有 17%（79-130 毫米）的降水损失到 T，E（10-35 毫米）和 I（15-38 毫米）对应 5%。尽管数据假设和简化存在固有的不确定性，包括数据插值误差，但与其他全球产品相比，耦合同位素质量平衡模型显示哥斯达黎加和圣卡洛斯集水区不同生态系统的合理水分配。