【作者】 林波；

【导师】 刘琪璟；

【作者基本信息】 北京林业大学 ， 森林经理学， 2013， 博士

【摘要】 湿地具有巨大的环境功能和效益,但近半个世纪以来在各种自然因素及人类干扰作用下,湿地的数量和面积锐减,服务功能退化严重。湿地水文情势的改变是湿地退化的最根本原因。利用水文模型能对湿地复杂的水文过程进行概化和模拟,尤其是具有物理基础的分布式水文模型能够反映流域产汇流的空间分布规律,模拟变化环境(如土地利用和气候变化等)下的水循环过程,可对湿地生态系统的管理、保护和恢复起到技术支撑作用。本研究的主要目标是基于分布式水文模型研究适宜我国三江平原地区的湿地生态系统管理、保护和恢复方法。为此,首先构建了一个概念性的集总式模型(NAM),以初步确定流域下垫面的水文特征参数,了解挠力河流域水文情势的变化及主要的影响因素。进一步,基于气象、水文、遥感和数字高程模型等多源数据集构建了挠力河流域地表水/地下水耦合模型(MIKE SHE/MIKE11),以流域内四个水文观测站1998～2000年逐日径流数据率定模型,以2003～2005年数据验证模型。进一步使用IPCC第四次评估报告公布的7个全球气候模式(GCMs)预估了流域2050s的气候情景,并基于这些情景模拟了未来气候变化对流域湿地水文情势的潜在影响。最后根据前面多个章节研究的结果,提出了适宜于挠力河流域的湿地生态系统管理、保护和恢复方案。研究的主要结论总结如下：(1)概念性集总式模型可以对挠力河流域降雨径流过程进行较好的模拟,模型在率定期的表现优于验证期。造成模型在验证期模拟效果降低的最主要原因可能在于农业开发活动对流域下垫面性质强烈而快速的改变。自20世纪50年代以来三江平原地区强烈的农业开发活动深刻影响了流域水文情势,并且这种影响在近20年仍然在持续。概念性集总式模型不确定性主要来源于输入数据、模型结构和最优参数集的选择。NAM模型只能对整个研究区的水文特性进行平均考虑,无法对融雪、人为干扰(抽水灌溉等)、不同土地利用类型的水文特性等进行深入考虑。(2)模拟和实测的水文过程线比较图以及定量的模型效果评价说明所构建的MIKE SHE/MIKE11耦合模型能够较好地模拟三江平原挠力河流域水循环过程,对湿地的管理和保护起到了技术支撑的作用。模型在率定期和验证期的Nash-Sutcliffe系数均达到0.65以上。水量平衡分析显示,模型率定期流域内总蒸散发量超过总降水量,流域处于水量损失的状态。对不同土地利用类型进行的水量平衡分析说明了湿地在调节区域气候和涵养水源方面的重要作用。流域内大面积农田采取的井灌措施导致了地下水水位的持续下降,农田抽水灌溉的吸水效应也对被农田包围的湿地和林地构成显著影响。模型不确定性的主要来源包括输入数据、模型结构和参数的选择。(3)GCMs对未来气候的预估结果表明,A2、A1B和B1.三个排放情景下挠力河流域在2050s年代的降水、温度和潜在蒸散发水平与基准期相比均有所提高,以A1B情景增加幅度最大。不同的气候模式对未来流域气候的预估趋势基本一致,但存在变动幅度大小的差异。气候变化的水文影响分析表明,未来流域内河道径流量在一年大部分时间都有所增加,以A1B情景增加量最高,集合平均模式AEM预测下游控制站菜咀子站的年径流总量在A2、A1B和B1情景下将分别增加7.7%,10.1%和6.8%。河道径流量的变化相对于降水量的变化有明显的延迟效应,这与流域中下游大面积沼泽湿地的蓄洪滞水和径流调节能力有关。未来流域总降水和蒸散发量都有明显升高趋势,但蒸散发的增加量较降水的增量更高。在全球气候变化的背景下,如果仍然维持当前的景观格局且不采取其它补水措施的话,未来挠力河流域的水资源供需矛盾将加剧,而流域内的湿地将面临更大的水量损失风险,极有可能进一步退化。气候模式的模拟结果也说明未来流域地表径流(坡面漫流)增加明显,如果不采取对应的防洪治涝和退耕还湿措施,流域将面临更大的洪涝灾害和水土流失风险。(4)根据水文模型模拟所反映的当前挠力河流域内湿地管理和保护方面面临的主要问题,提出了三种基本的湿地管理、保护和恢复方案(思路),分别对应着不同的湿地恢复强度和策略。方案一重点考虑核心湿地区的连续性,将处于成片湿地周边的破碎化农田等恢复为湿地,方案二将流域内全部水稻田恢复为湿地,方案三将流域内全部早地恢复为湿地。依据模型模拟结果并考虑现实可操作性,认为方案一在各个水文指标上均对流域湿地的保护具有积极正面的效果,且退耕还湿比例非常有限(耕地面积仅减少了6.68%),不会对农业生产造成显著影响,是一种合理且易于实施的最优方案。考虑到三江平原挠力河地区的流域特征以及该区湿地可能受到的未来气候变化的影响,实施湿地生态系统的管理、保护和恢复方案主要应从适当程度的退耕还湿、科学有效的生态补水、以及能落到实处的湿地生态环境保护等多方面开展。更多还原

【Abstract】 As one of the three biggest ecosystems on this planet wetland provides human beings with not only great amount of resources, but also precious environmental functions and benefits. However, wetlands in China have been suffering constantly from the global change and anthropogenic disturbance over the last50years. The cumulative effects of increasing wetland loss, as well as intensified adjacent land use continue to threaten the structure and function of wetlands. Water regime in wetland has been changed significantly in many regions, which is the main reason for wetland degradation. Models, especially physically-based distributed hydrological models, can often accurately represent complex wetland hydrological situations. They can provide us detail information of the watershed hydrological processes, and improve our understanding of the physical, chemical and biological processes within a watershed and the way they interact. Distributed hydrological models such as MIKE SHE, can also be used to simulate hydrological impacts of future climate and landuse change on the functioning of wetlands, which can be expected to benefit wetland management, protection and restoration.The main purpose of this thesis was to establish a framework for wetland management and restoration based on an integrated surface/groundwater hydrological modelling system, i.e. MIKE SHE. To achieve this goal, a lumped conceptual NAM model was firstly built to help understand the basic hydrology characteristics of the study area-Naoli River Basin in northeast China. Then, the coupled MIKE SHE/MIKE11model was constructed using multisource data, based on which the main hydrological process of the watershed was able to be simulated. Furthermore, seven Global Circulation Models (GCMs) and their arithmetic ensemble mean (AEM) were used to predict the climate patterns in 2050s under three emission scenarios (A2, A1B, and B1). Hydrological impacts of climate change upon the wetland was investigated by running GCM output through validated the MIKE SHE/MIKE11hydrological model. Finally, the optimal wetland management and restoration scheme was proposed based on the outputs from modelling. The main conclusions are summarized as follows:(1) The MIKE11HD/NAM modelling system is capable of simulating the rainfall/runoff process of Naoli River Basin. Model performance during calibration period was generally better than that during validation period with modification on underlying surface characteristics caused by intensive human activities. The ongoing agricultural development since1950s has significantly changed the hydrological regime of the watershed, and there is no sign that the wetland degradation trend has stopped currently. The uncertainty of our conceptual model comes mainly from input data, model structure and the selection of optimal parameter set. Although NAM can effectively represent the major hydrologic processes based on limited data and a modest number of parameters, it deals with each catchment averagely. Therefore, it is not able to adequately address problems such as snowmelt, irrigation and impacts of land use change on water regime.(2) Quantitative statistical parameters and visual comparison of simulated and observed hydrograph show that the MIKE SHE/MIKE11modelling system can effectively simulate the major hydrological processes of Naoli River Basin. The Nash-Sutcliffe coefficient during both calibration and validation periods was above0.65, a criterion as satisfaction. According to water balance analysis, the total evapotranspiration during the simulation period exceeded the total precipitation, and baseflow contributed a large portion to the channel flow, which means that the watershed was of deficit in water balance. Water balance analysis for different landuse types demonstrated the wetland’s important functions in climate regulation and water conservation. The widely adopted well irrigation, a conventional practice, in the area has led to the constant decline of groundwater level. The uncertainty of the coupling model lies mainly in the input data, model structure and the selection scheme of optimal parameter set.(3) On the whole, the GCMs predicted that the precipitation, evapotranspiration and temperature in the watershed would rise considerably in2050s under all the three emission scenarios, compared with the baseline situation. However, there were differences in the amount of variation between GCMs. The three scenarios show consistently greater discharge for most of the year, with A1B scenario the highest. The AEM predicted that the annual discharge in the downstream would increase7.7%,10.1%and6.8%for A2, A1B, and B1scenarios, respectively. There was a delayed river flow response to the changing precipitation in the lowland catchment, owing to the functions of water retention and runoff regulation of wetlands. Water balance analysis showed that annual total precipitation within the area would increase significantly, but annual total evapotranspiration would increase much more. If the current landscape pattern stays unchanged and no other recharge measures are carried out, the water shortage situation would be more severe in the context of global climate change. Wetlands within the watershed are at greater risk of being shrunk and degraded.(4) Based on the conclusions of modelling practice, three wetland management and restoration-planning schemes (corresponding to the relevant regulation strategies and strength) have been presented. Scheme1concerns mainly on the continuity and integrity of the core wetland area, and it reconverts the fragmental croplands into an integrated wetland with the relatively virginal remnant. Scheme2reconverts all the paddy field while Scheme3all the dryland within the watershed into wetland. According to modelling results, Scheme1is optimal, as it is favorable to wetland protection in terms of most hydrological indicators and no harm on food security in the region would be expected. Considering the geohydrologic conditions of the Naoli River Basin, as well as the potential impact of climate change, the planning scheme should be carried out from the following aspects:reconversion of cropland into wetland at a rational level, effective water recharge, and wetland environmental protection.更多还原