西北干旱区泡泡刺灌丛的降雨再分配特征及影响因素分析

Abstract

定量分析植被冠层对降雨再分配过程的影响, 是认识陆地生态系统水文循环的重要环节。然而, 由于干旱区天然植被分布稀疏、形态结构特殊, 其降雨再分配过程的测算较为困难, 相关研究较少, 特别是关于荒漠低矮灌丛的降雨再分配研究鲜有报道。本文以河西走廊中段临泽绿洲—荒漠过渡带的天然建群种泡泡刺灌丛(Nitraria sphaerocarpa)为研究对象, 基于3年逐个单次降雨事件的观测数据分析了生长季泡泡刺灌丛的降雨再分配特征及主要影响因素, 量化了泡泡刺灌丛覆盖下实际进入土壤的有效降雨量及其空间分布特征。结果表明：(1)生长季泡泡刺灌丛的平均穿透率、树干茎流率和冠层截留损失率分别为87.89%、1.61%和10.50%；(2)降雨量是影响泡泡刺灌丛降雨再分配特征的关键气象因素, 其与穿透雨量、树干茎流量、冠层截留损失量之间具有显著的统计关系(P < 0.001)；(3)与干旱区其他稀疏植被相比, 泡泡刺灌丛的穿透率和集流率较高, 冠层截留损失率较低, 与其特殊的植被形态特征有关, 相关分析的结果表明, 泡泡刺灌丛的穿透雨量与植被面积指数和株高呈显著的负相关关系(P < 0.001), 树干茎流量与树干倾角呈显著的正相关关系(P < 0.01)。这些研究结果增进了我们对于绿洲—荒漠过渡带植被对局地水文过程影响的认识, 为合理估算干旱区稀疏植被覆盖下的冠层截留损失提供了方法参考。;Analyzing quantitatively the effect of vegetation canopy on rainfall partitioning is an important part for better understanding the hydrological cycle in terrestrial ecosystems, which is particularly useful for hydrologic budget estimation, hydrological models' establishment and afforestation projects' implement in drylands. However, it is difficult to measure and calculate its rainfall partitioning process of the natural vegetation in the drylands due to its sparse distribution and special morphological structure, and very few field measurements have conducted specially for the natural desert dwarf shrub species, which distributed widely in the oasis-desert ectone of northwestern China. Here we present results of the partitioning of rainfall into throughfall (TF), stemflow (SF) and interception loss (IL) by a shrub species Nitraria sphaerocarpa, a naturally dominant species of Linze oasis-desert ecotone in the middle part of the Hexi Corridor, based on the observation data during the growing season for 3 years. Consequently, the effective rainfall that actually enters the soil and its spatial distribution characteristics beneath the N. sphaerocarpa canopy are quantified. We also analyze the influencing factors for rainfall partitioning by N. sphaerocarpa canopy. The results show that: (1) on average, the measured throughfall, stemflow and derived interception loss by N. sphaerocarpa during growing season account for 87.89%, 1.61% and 10.50% of gross rainfall amount, respectively. The average funneling ratio for N. sphaerocarpa is (129.66 ±93.01) and its canopy storage capacity is 0.42 mm. N. sphaerocarpa's throughfall is produced from rainfall events with total amount more than 0.2 mm, while its stemflow does not occur following rainfall events less than 1.5 mm. (2) Rainfall amount is the key meteorological factor affecting the rainfall partitioning characteristics. There are significant correlations between rainfall amount and throughfall, stemflow and interception loss (P < 0.001). Other meteorological variables like canopy surface temperature, atmospheric temperature, atmospheric humidity and vapor pressure can also affect rainfall redistribution process. (3) Compared with other sparse vegetation in drylands, the N. sphaerocarpa has higher throughfall percentage and funneling ratio, but lower interception loss percentage. Special canopy morphology of N. sphaerocarpa may play an important role in its pattern of rainfall partitioning. Pearson correlation analysis shows that throughfall has significantly negative correlation with plant area index (PAI) and shrub height (P < 0.001), and stemflow has positive correlation with stem orientation (P < 0.01). Other canopy morphology like bark roughness, leaf shape and canopy form, which lack of quantitative description, are also vital for rainfall partitioning patterns. The results might improve better understanding of shrubs' role on the local hydrological processes in oasis-desert ecotone, and provide a reasonable method for estimating interception loss by sparse vegetation in drylands.