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题名: 祁连山区水源涵养功能时空变异 及增贮潜力
作者: 田菲
学位类别: 博士后
答辩日期: 2016-03
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 傅伯杰
关键词: 祁连山区 ; 水源涵养 ; 水文过程 ; SWAT模型
学位专业: 环境科学与工程
中文摘要:     针对祁连山区特殊的地理区位和关键生态功能,系统评估水源涵养功能的时空变异及增贮潜力,阐明退耕还林、天然林保护等重大生态工程对区域水源涵养功能的影响,对于维持整个流域的生态系统和社会经济的健康发展,生态功能非常重要,对河西走廊内陆水系及其它气候干旱、水资源匮乏的干旱、半干旱区的生态健康和经济社会发展具有重要意义。
    本文以黑河上游祁连山区为研究对象,基于 SWAT模型,以不同时空尺度的土壤含水量模拟为突破点,定量评估了祁连山区 1971-2010年过去40年的水源涵养功能动态变化,简要阐明了退耕还林、还草等重大工程对区域水源涵养的初步影响。以 1971-2010年为基准期,以全球变化背景下可能出现的   25种不同气候变化情景、4种土地利用情景为假设条件,模拟出各种气候、土地利用变化情景下区域水资源状况,并估算对于基准期的变化率,分析区域水源涵养功能对叠加“气候变化”及“生态工程建设”的响应程度,定量评估了祁连山区水源涵养功能时空分布及增贮潜力。
    研究结果表明,重大生态工程如退草还林实施以后,土地利用类型变化显著。在 2000年,农田占0.04%,在 2010年上升到  0.19%。林地面积从 584km2增加到 1608 km2,增加了176%;高覆盖度草地增加了200 km2(5%)。相应的,中低覆盖度草地有所下降,分别减少了 25%,21%。因此,对于该研究区,实施生态工程建设,主要是退草还林。
    基于  SWAT模型月径流量实测与模拟值在校正期和验证期的拟合表明,实测径流与模拟径流的拟合度较高。不论是R2还是 E,验证期明显高于校正期.在验证期,R2  = 0.96,E  = 0.93;在校正期,R2= 0.93,E = 0.88。验证期的平均相对误差为  3.51%,在校正期为  5.68%,因此,验证期的精度明显高于校正期。模拟值与实测值吻合较好,月尺度的模拟结果明显高于年尺度。但年尺度的模拟精度能达到乙级水平(0.70-0.90)。在模型校正期和验证期 E的平均值分别达到了0.80和  0.85,个别年份还达到了甲等水平。因此,该模型能较为准确的模拟该区的径流量,模拟结果也可为流域水资源管理提供理论依据。
    中低覆盖度草地恢复为高覆盖度草地和林地之后,祁连山区的产流和土壤含水量分别增加了 32%,46%,而地表径流量和蒸散发量分别减少了 48%,4%。减少了地表径流,提高了土壤入渗能力,增加了土壤含水量,发挥了保持水土、涵养水源的功能。不同土地覆被类型 1971-2010年   40年的模拟结果来看,产水量林地  (70.7 mm) >低覆盖度草地(66.9 mm)>高覆盖度草地(56.1 mm) >中覆盖度草地  (27.4 mm);蒸散发量中覆盖度草地最高  (175.6 mm),比林地高 24.9%。但从径流量的变化来看:高覆盖度草地  (49.8 mm)  >中覆盖度草地(20.6 mm),林地没有径流量产生。相应的,林地的土壤水储量最高(43.1   mm),比高、中覆盖度草地分别高  65.2%,31.5%。从土壤含水量的空间分布来看,高郁闭度林地为主的子流域土壤水储量较高,达到 35mm。
      另外,气候变化在区域水文过程中扮演了重要角色,尤其对土壤水储量和产流量的影响更加明显,但土地利用和土地覆被的影响却是至关重要的。气候变化造成的土壤水储量最大变化幅度为 37%,发挥了巨大的增贮潜力,然而土地利用变化造成的土壤水储量变化可以达到 1.57倍,即增贮幅度超过50%。全林地情景比裸地情景更容易受暖干化的影响,在区域尺度上,土地覆被和气候变化叠加了这种生态水文效应,一定程度上可能给水资源可持续发展带来非常大的压力。盲目实施区域退耕还林政策,会造成地表径流明显减少,对下游来水量的贡献减少,造成干旱区的干旱化趋势更加剧烈。但某种程度上改善了本区域的土壤水储量,在本区域充分发挥了保持水土、水源涵养的功能。因此,在缺水严重的干旱半干旱区,需要科学的权衡生态环境的可持续发展与水资源安全问题。
英文摘要:       Qilian Mountain is an important ecological functioning zone nourishing the oasis in northwest China. Due to the unsustainable use of the forest, the oasis ecosystem was seriously  damaged and  experienced  deterioration of  its  ecological environment.  To alleviate this situation, government has adopted ecological engineering such as “Grain
for Green”  program,  “Natural Forest  Protection Project”  and  “ Three-North-Shelter Forest Program”  in this region. Addressing  the long term  effects of vegetation  based campaigns on water  balance or the temporal  and spatial variability of  water retention and its increase potential is quite important for the maintenance of a healthy ecological system, and  will  provide implications  for eco-environmental  restoration program  in China, and be applicable to other arid and semi-arid region of the world.
      Results indicated  that land  use and  cover experienced  great changes.  Farmland covered about 0.04% of the land  area in the 2000s, as opposed to 0.19%  in the 2010s.Forest expansion was  most evidently from 584 km2 during  past  decades.  The   high  coverage  grassland  (vegetation  coverage>50%)expansion was not as  obvious as forest, it also increased  by 200 km2(5%). Compared to 1608 km2, increased by 176% above mentioned, the medium(20% < vegetation coverage < 50%)  and low coverage grassland (5%  < vegetation coverage  < 20%)  has experienced  great decrease, which achieved to about 25%, and 21%, respectively.                     
      The  calibration  and  validation  with  SWAT  model  at  the  monthly  scale  was satisfactory, as  indicated by  high values of  R2 and  most of data  points were  closely distributed around the 1:1  line. At monthly time steps,  the model performance during the validation period was  better than calibration period, with high  values of R2 (R2 =0.96) and E (E = 0.93), and low values of relative error (3.51%). R2 and Nash–Sutcliffe coefficients for calibration  period reach 0.93, and  0.88, respectively. And the average value  of relative  error  was only  5.68%,  indicating that  the  SWAT model  generally exhibits a good performance in the study area. At yearly scale, the model performance (R2 = 0.88)  was not as  good as that  in monthly steps, however,  the evaluation result was acceptable.
      In this study, the study region is the upper Qilian Mountain, and the study focus is that the land degradation is a global eco-environmental issue, to minimize  soil erosion and  land degradation,  China  has  implemented several  ecological  engineering since 1999. Relationships  between vegetation  and water  budgets has been  widely studied, however, very  few studies  addressed the effects  of eco-environmental  restoration on water  balance in  mountain areas,  especially  with a  focus  on soil  moisture  content.Therefore  SWAT model  was used  to  quantify the  effects  of ecological  engineering actions  on  water   balance  based  on   baseline  scenarios,  four   different  vegetation scenarios,  and twenty-five  future  climate scenarios.  Results  indicated that  after  the ecological engineering, water yield and soil water content experienced an increment of 32%, and  46%,  the opposite  trend was  monitored in  runoff  and evapotranspiration,which decreased by  48% and 4%, respectively.  Therefore ecosystem restoration have increased soil  water retention capacity,  a greater proportion  of precipitation  reaching the catchment is  absorbed by the soil  rather than flowing  out of the region  as runoff.
    The annual water yield from forest was 70.7 mm on average, and then followed by low and  high coverage  grassland,  with values  of  66.9 mm,  and  56.1  mm, respectively. Medium coverage grassland has the lowest values of 27.4 mm, about 61.2% lower than forest. The evapotranspiration change  case noted inversely with  water yield. Medium coverage grassland presented the highest evapotranspiration  with 175. 6 mm, that was 24.9% higher than forest. Generally, the evapotranspiration of high coverage grassland is much greater  than that of  low coverage grassland, which  exceeds that of  forest. In contrast to  the water  yield  and evapotranspiration,  the annual  runoff from  high and medium coverage  grassland  varied from  49.8 mm  to 20.6  mm.  The forest  and low coverage grassland  absorbed part  of the  lateral water  flow as  well as  generating no runoff from  precipitation. This is  clearly demonstrated  by the changing  trend of soil water content.  Generally, the soil  water content was  relatively stable,  except the wet years. Forest has the highest values of soil water content (43.1 mm), which was 65.3%,and 31.5%  higher than  high  and medium  coverage grassland,  respectively. Besides,subbasins that with high forest content has highest soil water content (35 mm).
    Besides, results  also suggested  that the  mean  annual evapotranspiration  changes only 7.2% from barren case to 100% forest case, however, it produced 35.2% reduction in average  annual streamflow,  and 157%  increase in  soil water  storage. Changes  of evapotranspiration  and streamflow  was  only 0.3%,  and  -0.9%  at T  +  3.9℃   when compared to the historic scenarios in barren cases, while for forest case, variations were 3%, and -21.8%,  respectively. Vegetation greening induced more  remarkable changes in  hydrological components  than  those  resulted  from climate  change.  Our  what if research  provide   new  insights   for  promoting   sustainable  management   of  water resources and ecosystems in mountainous water source areas.

 
 
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36964
Appears in Collections:城市与区域生态国家重点实验室_学位论文

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Recommended Citation:
田菲. 祁连山区水源涵养功能时空变异 及增贮潜力[D]. 北京. 中国科学院研究生院. 2016.
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