Abstract:

[Objective] In this study, the distribution characteristics of throughfall under the Caragana tangutica shrub canopy and its influence factors were researched. The aims of this paper were to provide the basal data for quantitatively evaluating the eco-hydrology function of Caragana tangutica shrub in the Qilian Mountains as well as parameterized the hydrological model which relying on the ecological process. [Method] Based on the investigation of population characteristics, three representative Caragana tangutica shrubs were selected on the middle slope. The measurement radial sections along the branch radial direction were selected. Containers for rain water collection were installed at each radial section. The throughfall and its spatial distribution were measured after 12 rainfall events at the period with stable foliage volume. Then the relationship between throughfall and rainfall, as well as the spatial distribution pattern and its influence factors were analyzed. [Result] The throughfall under Caragana tangutica canopy exhibited evident differences in different rainfall events. In the observation period, the mean throughfall rate of individual shrub was 45.9%. There was a linear relationship(y=0.626 2x-1.018 1,R²=0.983) between throughfall volume and rainfall and a quadratic function relationship between throughfall rate and rainfall(y=-0.033 6x²+1.806 8x+34.094,R²=0.575 3). The throughfall rate exhibited an evident spatial heterogeneity and monotonously increased from 28.98% at 10cm distance to the shrub base to 62.19% at 90cm distance to the shrub base along the radial direction. Influenced by the canopy structure characteristics, the biggest increment was occurred at a distance of 30—50 cm, which accounted for 61% of the total increment. The spatial variable coefficient of throughfall rates along the radial direction were decreased with the increasing rainfall, which expressed more remarkable when the rainfall was less than 10 mm. The distribution pattern was also changed when the rainfall intensity was increased. When the rainfall intensity were 0.97 or 4.27 mm·h^-1, there was an evident difference of throughfall rates between 10—30 cm and 50—90 cm, while this difference could be weaken when the rainfall intensity was 25.06 mm·h^-1.[Conclusion] The throughfall features of individual Caragana tangutica shrub were influenced by characteristics of both rainfall and the canopy structural. The relationships between throughfall volume and rainfall as well as between throughfall rate and rainfall were in accordance with findings of correlational researches that conducted by predecessors. The general spatial distribution pattern of throughfall under the canopy was determined by the canopy features, while this pattern was also influenced by rainfall volume and rainfall intensity. The increase of rainfall or when the rainfall intensity reached a certain extent both can decrease the spatial heterogeneity of throughfall under the canopy.

Key words: Qilian Mountains, Caragana tangutica shrub, throughfall, spatial distribution