Dynamic Rainfall-Partitioning Relationships among Throughfall, Stemflow, and Interception Loss by Caragana Intermedia

Grassland restored by re-vegetated shrub is an important ecosystem in desert steppe of Northwest China. Yet little is understood about the underlying eco-hydrological mechanisms for maintaining the stability of the re vegetated ecosystem. Based on the conversion relationships among throughfall, interception loss, and stemflow, we developed a method to analyze the dynamic responses of rainfall partitioning by vegetation canopies to precipitation variation, and the driving mechanisms for stemflow of two morphological distinct shrubs (unhealthy and healthy C. intermedia) during the 21 rainfall events (0-15 mm) in the period from 2016 to 2017. We found that the stemflow increased in a low-value stepwise manner with the increasing rainfall depth and eventually became scattered. Therefore, the response of stemflow to gross precipitation was divided into three stages by rainfall depth: initiation (0-2 mm), transition (2-6 mm), and scattered (6-15 mm). A significantly negative linear relationship was observed between throughfall and interception loss, while the relationships of interception loss- stemflow and throughfall- stemflow exhibited a more complex nonlinear way with relatively weaker correlations. Rainfall depth and canopy area were two main factors driving the partitioning relationships. Non-precipitation meteorological factors were dominant in the 0-2 mm rainfall events, while rainfall factors were determinant in the 6-15 mm events. Morphological factors exerted more influences on the partitioning relationships for healthy C. intermedia. Overall, the conversion between throughfall and interception loss was the majority of dynamic rainfall partitioning; therefore, low and unstable stemflow was usually inevitable. The results indicate that the precipitation threshold for stemflow generation should be a range value instead of a specific value, and the rebuilt analysis roadmaps are essential for investigating stemflow using the thorough conversion relationships and the 'stepped' approach.