【作者】 邵薇薇；

【导师】 杨大文；

【作者基本信息】 清华大学 ， 水利工程， 2009， 博士

【摘要】 非湿润地区植被与流域水循环的相互作用机理,是流域生态水文学的研究热点之一。在缺水环境下植被的生长主要由可利用水分的多少决定;而植被在生长过程中通过冠层截留及蒸腾等影响流域的水文循环。近几十年来,由于森林砍伐、过度耕作和不合理的水资源开发等,导致了我国北方非湿润地区的严重生态和环境问题。因此,研究植被与流域水循环的相互作用机理,是解决非湿润地区生态环境问题的迫切需要。论文以我国内陆河流域、黄河流域和海河流域为研究区域,基于相关分析、水热耦合平衡原理、生态水文模型、分布式水文模型等不同方法,探讨了植被与流域水循环的相互作用机理。论文利用气象、水文、土壤水分及植被等数据,采用相关分析方法,研究了植被覆盖率与水循环要素的关系。分析结果表明,在相对湿润的流域中,植被覆盖度越高,蒸散发越大,并伴随着蒸发效率越高但蒸发系数越低,地下径流占总径流的比例越高,平均土壤水分越大。根据水热耦合平衡原理,分析了植被在Budyko曲线上的分布,并将植被覆盖度引入流域水热耦合平衡模型,改善了流域蒸散发的模拟结果,阐释了气候和植被覆盖度对流域水量平衡的影响。基于Eagleson的生态水文模型,从植被生长季节平均的流域水量平衡关系入手,分析并揭示了流域长期平均的植被覆盖度和土壤水含量的区域分布特性以及年际变化特性,建立了植被覆盖度与土壤含水量之间的定量关系。将水热耦合平衡原理和生态水文模型耦合,提出了可用于预测气候和植被变化下流域水循环响应的方法。基于分布式水文模型(GBHM)与流域水热耦合平衡模型的模拟分析,揭示了实际蒸散发与潜在蒸散发之间在流域和年尺度上呈非线性互补关系,但在山坡和小时时间尺度上呈线性正比关系;并发现土壤水分和植被参数化对流域水循环模拟结果的影响,随着时间尺度变小表现得越来越显著。论文对植被和流域水循环相互作用机理的研究,为理解我国非湿润地区植被变化与水循环之间的关系,以及预测气候变化下的流域生态水文响应提供了参考;并为评价我国北方地区的水土保持工程对流域水循环和水资源的影响提供了理论基础。更多还原

【Abstract】 Analysis on the spatial and temporal relationships between vegetation dynamics and hydrologic cycle is one of the hot spots in ecohydrology. The growth of vegetation is controled by water availability, while vegetation growth also feeds back to influence regional water balance. A better understanding of the relationship between vegetation state and water balance would help explain the complicated interactions among climate, vegetation and the catchment hydrological cycle. In the present study, the non-humid regions in China are selected as the study area, including the Loess Plateau and the Tibetan Plateau in the Yellow River basin, some Inland River basins, and the Hai River basin. Based on the correlation analysis, the coupled water-energy balance principle, the ecohydrological model and the distributed hydrological model, this research is aimed to explore the mechanism of interaction between the vegetation and catchment hydrological cycle.Firstly, the correlation between vegetation and components of the catchment hydrological cycle is analyzed based on long-term climate, hydrological and vegetation data. The results indicate the vegetation coverage is higher in the relatively wetter environment, associated with a higher evapotranspiration. In the catchment with higher precipitation, the inter-annual variation of regional NDVI is lower. An increment of the vegetation coverage comes with an increase of the evaporation efficiency but a decrease of evaporation ratio. Higher vegetation coverage, ratio of the base flow to the total flow is higher. Soil moisture and the regional vegetation coverage show a positive correlation.Then based on the coupled water-energy balance principle, the impact of vegetation on catchment water balance is analyzed. The distribution of vegetation coverage on the Budyko curve helps to explain why the wetter environment has higher vegetation coverage associated with higher evapotranspiration efficiency. It is also suggested the regional long-term water balance should not vary along a single Budyko curve; instead it should form a group of Budyko curve owing to the interaction between vegetation, climate, and hydrological cycle. Vegetation coverage is successfully incorporated into an empirical equation for estimating the catchment landscape parameter in the coupled water-energy balance equation in order to improve the spatial and inter-annual simulation of the actual evapotranspiration.Based on the catchment ecohydrological model developed by Eagleson, from the water balance analysis for the vegetation growing season, the allocation of evpotranspiration flux among canopy transpiration, surface interception, and bare soil evaporation is analyzed. The quantitative relationship between the vegetation coverage and soil moisture is derived, which would be useful for predicting the change of vegetation coverage due to climate change and human activity. Coupling water-energy balance model and the ecohydrological model, a new model is developed for predicting the impact of climate and vegetation changes on the catchment water balance.The vegetation parameterization scheme in the catchment hydrological simulation is discussed. A distributed physically-based hydrological model (GBHM) and the water-energy balance model are used to predict actual evapotranspiration in the Luan River basin. From the analysis at different time scales through comparison of these two models, it is shown that catchment annual evapotranspiration is controlled mainly by the annual precipitation and potential evaporation, variability of soil water and vegetation become more important at a smaller time scale. It is also known that the relationship between potential and actual evapotranspiration shows a highly nonlinear relationship at the annual and catchment scale, but can be simplified to a linear relationship at hourly temporal and hillslope scales.This research is potentially useful for assessing the long-term effect of vegetation changes on catchment hydrology, and hence has implications to the water resources management in the non-humid regions of China.更多还原