【作者】 周艳春；

【导师】 许士国； Yongqiang Zhang；

【作者基本信息】 大连理工大学 ， 水文学及水资源， 2013， 博士

【摘要】 全球气候变暖导致森林火险天气增加,森林火灾的发生机率呈上升的趋势。森林火灾通过影响植被、地表枯落物、土壤及生态环境等影响降雨截留、土壤蓄水量、蒸散发及径流量等流域水循环的各个环节。在气候变化的背景下,森林火灾水文响应的研究有助于揭示森林流域的水循环机制,为流域范围内森林资源和流域水资源的合理规划管理提供科学依据,促进陆地生态系统的可持续发展。目前,森林火灾的水文响应受到国内外学者的广泛关注。本文以发生在澳大利亚维多利亚州的1983和2003年的两场森林大火为例,采用统计分析与水文模型模拟相结合的方法,开展森林火灾对流域蒸散发和径流影响的研究,并尝试在降雨-径流模型中考虑土壤含水量和植被动态信息提高受火灾干扰流域的径流模拟精度。主要研究内容及结论如下：(1)研究流域的气候向有利于林火发生的方向演变。选取与林火发生条件密切相关的四个气象指标(气温(最高温、最低温及平均气温)、降水量、相对湿度及潜在蒸散发),采用5年滑动平均及距平分析相结合的方法,分析各气象指标在研究时段内的发展趋势,结果表明,研究流域的气候有变暖变干的趋势,有利于林火的发生,要做好林火的预防工作。(2)森林火灾烧毁地表植被,影响流域蒸散发的时空分布。森林火灾导致火灾当年流域平均叶面积指数和地表反照率骤减,而后,伴随植被的恢复逐渐恢复。地表反照率的变化反映了地表辐射平衡的变化,从而影响流域的蒸散发水平。对比火灾前后流域蒸散发时空分布的变化,发现森林火灾对流域蒸散发的影响与火烧的严重程度有关。火烧严重的区域,蒸散发的减少幅度较大,反之,较小。伴随植被的恢复流域的蒸散发有增加的趋势。(3)利用水文模型模拟并量化了森林火灾对流域径流量的影响。利用澳大利亚的AWRA-L、我国的新安江和法国的GR4J三个水文模型分别模拟火灾前后各流域的基准径流过程,进而估算森林火灾对流域径流量的影响。首先,考虑到火灾后气候有变暖变干的趋势,为了确保模型在火灾前率定的参数可以有效的应用到火灾后的研究时段,选择属性相似距离相近的未受火灾影响的四个流域进行参数移用的有效性验证；其次,将三个研究流域火灾前率定的参数应用于火灾后模拟森林火灾对流域径流过程的影响。分析发现,在火灾前后气候条件稳定的条件下,森林火灾是灾后短期内径流增加的主要原因,伴随植被的恢复森林火灾引起流域产水量增量的减小。(4)考虑火灾引起植被及土壤水动态的变化,模拟了森林火灾的径流响应过程。针对集总式降雨径流模型中很少考虑植被动态信息的不足,将土壤含水量与遥感植被动态信息与Penman-Monteith模型相结合,改进新安江模型,进而提高受火灾干扰流域的径流模拟精度。本文以新安江模型为例,采用考虑土壤含水量动态及植被动态信息的Penman-Monteith模型对新安江模型中的三层土壤蒸发模型进行改进。将改进的新安江模型在受2003年森林火灾影响的4个研究流域应用,改进新安江模型的率定期和验证期的模拟精度均有一定提高。为了进一步说明植被动态信息对径流过程的影响,本文设计了3个反映不同植被信息的实验方案在验证期对改进模型进行测试。对比3个实验方案发现,利用植被动态信息的实验方案径流模拟精度有所提高,纳什效率系数(NSE)提高了1%-7%,模拟误差降低了3%-11%,说明集总式降雨降雨径流模型中考虑植被动态信息可以提供径流模拟的精度。综上所述,本研究可以为我国在森林火灾对流域水文过程的影响研究方面提供借鉴和参考,并为我国森林火灾后水资源的合理规划利用提供科学依据。更多还原

【Abstract】 Forest fires show an increase due to the increase in forest fire weather (low precipitation and relative humidity, high temperature and wind speed) caused by gobal warming. Forest fires affect catchment hydrological cycle, including reduced infiltration rates caused by changes in soil properties, reduced evapotranspiration rates caused by loss of vegetation and surface litter and destroyed ecological environment. The hydrological effects of forest fires have been recived wide attentions from scholarsathome and abroad. In the context of climate change, researches on hydrological response to forest fires help to reveal the water cycle mechanism, to rationally allocate forest and water resources and to promote the sustainable development of terrestrial ecosystems in forest catchments. Taken two forest fires (1983and2003bushfire) in the state of Victoria, Australia as examples, statistical method and hydrological modeling are used to evaluate forest fire impact on evapotranspiration and streamflow. In order to improve runoff estimates, this paper incorporates soil moisture and vegetation dynamic into rainfall runoff model. The main focus and conclusions of this study are as follows:(1) Forest fire weather is greatly affected by climate and weather conditions. Four meteorological indexes are selected to analyze climate change impact on the chances of a fire starting. They are temperature (maximum temperation, minimum temperature and mean temperature), precipitation, relative humidity and potential evapotranspiration, respectly. The5-year moving average method and anomaly analysis are used to test changing trend of the four indexes in the test period. The results show that the regional climate becomes warmer and drier. It shows an increase chance of a fire starting. Preventing work should be ready for forest fires.(2) Forest fires show impacts on evapotranspiration through destroying vegetion cover. Forest fires result in a noticeably reduction of mean leaf area index (LAI) and surface albedo in the year of fires. Then, LAI and surface albedo gradually recover along with vegetation recovering. Changes in suface albedo reflect changes in the surface radiation balance, thus affecting evapotranspiration rates at catchment scale. The impact of forest fires on evapotranspiration is related to fire severity. The more severe the fires are, the more evapotranspiration reduces. Conversly, the less evapotranspiration reduces. Subsequently, the evapotranspiration increases along with vegetation recovering. (3) This paper presents the impact of forest fires on streamflow using hydrological modeling approach. The hydrological models are used including AWRA-L, Xinanjiang and GR4J model from Australia, China and France, respectively. Firstly, the applicability of hydrological modelling to quantify bushfire impact on streamflow mainly depends on how the model parameters are calibrated and how they are transferred from calibration period to simulation period. It is important to investigate the transposability of model parameters in time (i.e., to make sure that their estimation is not dependent on climate characteristics of the calibration periods). This can provide us with a better understanding of uncertainty associated with using hydrological models for quantifying bushfire impacts on streamflow. Four median-size catchments close to the three study catchments are selected to investigate the model transposability. Validation results provide confidence in the bushfire impact assessments based on hydrological modelling. Secondly, the three hydrological models are used to quantify the bushfire impact on streamflow. The results show that there is a substantial increase in streamflow after the immediate1983bushfires that is not attributable to climate. Then, the increment of streamflow is reduced due to plantation recovering.(4) Soil moisture and remotely sensed vegetion dynamic information are incorporated into Penman-Monteith (PM) equation. Xinanjiang model is modified by replacing the original three-layer with one-layer evapotranspiration sub model (PM equation) to improve runoff estimates for four south-east Australian catchments which experienced severe bushfire impacts. The three modeling experiments are designed for the modified Xinanjiang model (XAJ-ET) to investigate the simulation capability of the modified model in four forested catchments which were affected by extensive bushfires in January2003. The improvement is indicated by a slight increase (1%-7%) in the Nash-Sutcliffe efficiency of daily runoff and noticeable decrease (3%-11%) in volumetric errors. It indicates that incorporation of vegetation dynamic data into Xinanjiang model can improve runoff simulation efficiency.更多还原