【作者】 方克艳；

【导师】 勾晓华； 陈发虎； Edward Cook；

【作者基本信息】 兰州大学 ， 自然地理学， 2010， 博士

【摘要】 理解我国西北地区水文气候的时空特征及其与亚洲季风动态的联系对该地区水资源保护以及生态环境可持续发展具有重要意义。本文利用树轮指标探讨西北不同地区不同海拔高度树轮气候作用关系的异同,重建西北地区不同区域干旱指数和降水的变率,并探讨其与亚洲季风动态的联系。(1)树轮年表建立本文首先讨论了同一采样点内树轮生长与气候关系出现分异的情况,以及树轮序列标准化过程中可能出现的始端拟合问题和末端拟合问题。针对这些问题,本文建议野外采样时详细记录每棵树的生境,分析单个树轮序列生长特征及其与气候的响应关系,剔除个别由于生境差异而出现不同的树轮气候响应特征的样芯,比较不同样芯轮宽指数与年表指数的差异,选择适合的拟合曲线处理那些发生较大生长干扰和存在始端拟合问题的样芯。(2)树轮气候响应分析通过对祁连山东部的兴隆山、吐鲁沟和磨石沟三个山体树轮特征值和树轮气候响应关系的研究,发现区域树轮普遍表现出与温度负相关、与降水正相关以及与干旱指数更显著的正相关。结合阿尼玛卿山、祁连山中部和这三个山体的树轮指数的研究发现,树轮低频变化更多响应温度而高频变化更多响应降水；树种差异对树轮气候响应有影响,例如油松的树轮气候响应在高频上更显著而云杉的树轮气候响应在低频上更显著。通过对峨眉山和兴隆山顶部三个不同海拔样点的分析发现兴隆山顶部样点树轮生长表现出与干旱的负相关,峨眉山一个样点由于高位沼泽化的发展,导致该点干旱化趋势减弱。为了进一步了解树轮生长和树轮气候响应的时空特征,本文收集了西北地区的64个树轮年表的树轮网络。根据研究区树轮生长特征差异,将区域树轮生长划分为9个区,分区内部树轮共同信号强度的增强往往对应着气候极端事件的发生。西北地区多数树轮生长受到当年和前一年生长季干旱的限制。研究还发现树种差异和气候梯度都影响树轮气候响应关系,而气候的差异是影响树轮生长的主要因子。(3)单点树轮干旱重建由于西北地区树木生长主要表现为受干旱影响,因此本文在西北不同地区利用树轮宽度重建了干旱干旱指数。研究分别重建了兴隆山和贵清山210年和391年以来干旱指数的变化,解释方差分别达到40%和49%。研究还对比分析了中东亚干旱半干旱地区和典型季风区区域干旱历史的异同。为了弥补我国南方可共享的树轮干旱重建的不足,还重建了横断山地区568年以来的干旱历史。基于中东亚干旱半干旱地区6个干旱重建与典型季风区7个干旱重建的对比研究发现,中东亚干旱半干旱地区东西部干旱历史区别大而典型,季风区南面和北面差别大。(4)面域树轮干旱重建本文基于中国西北以及周边地区的干旱指数栅格数据把研究区划分为“西部区”和“东部区”,并根据研究区内部的130个树轮年表,分别重建了“西部区”1587年以来和“东部区”1660年以来的干旱历史。本文还采用“搜索相关系数”方法,探索了我国西北地区降水点对点的重建。基于我国西北地区26个基本站降水重建数据,本文对西北地区降水与太平洋和印度洋海温进行奇异值分解,找出了海温-西北降水遥相关作用的关键区域。更多还原

【Abstract】 Drought variability of northwestern (NW) China is of serious concern due to its significant impacts on local ecosystems and human populations. Tree rings were used in this thesis to reconstruct the spatiotemporal features of the drought variability over the past 400 years. The reconstructions enable scientists and policy-makers to place the recent drought events into a longer context of climate change to evaluate its severity.For these purposes, the author first discussed the "start-fitting" and "end-fitting" problems on the standardization of tree rings. The earlier one indicates that the determinisitive fitting curves (e.g. negative exponential or Hugershoff curves) tends be biased close to the pith. The latter one suggests that any changes in tree growth occurred in a given period are able to change the entire deterministive fitting curve, leading to biased tree-ring indices. It is also suggested to testing the homogeneity of tree rings and climate associations prior to the establishment of a tree-ring chronology.Investigations on tree growth and climate-growth relationships along altitudinal gradients at Xinglong Moutain, Tulugou and Moushigou indicated that tree rings showed negative correlations with temperature and postive correlations with precipitation and higher correlations with drought indices, indicating a drought-stressed pattern. It is, however, not the case for the high-altitude sites over at Anyemaqen and central Qilian Mountain where tree growth shows positive correlations with temperature. Tree rings at the uppermost site at Xinglong Mountain showed negative correlations with Palmer drought severity indices (PDSI). A middle-altitude at Mount Emei showed decrease in drought association due to the acidophilous induced "swamping-type effect".A comprehensive investigation on the spatiotemporal characteristics of tree growth and climate-growth associations was performed on 64 chronologies in NW China. These tree-ring chronologies were classified into 9 groups. The common signal strength between chronologies tends to increase in severe dry or wet epochs for most of the groups. The climate-growth relationships are classified into 8 clusters based on their tree-growth features. Most of the tree rings are close related to drought conditions in growing seasons of current and previous years. The features of climate-growth relationships are associated with to the tree species and climate gradients.Tree rings at Xinglong Mountain and Guiqing Mountain were used to reconstruct the regional PDSI from 1794 to 2003 and for the period 1618-2005, which explain 40% and 49% of the total variance, respectively. The thesis compared 6 drought reconstructions of central high Asia and 7 reconstructions in monsoonal Asia. A PDSI reconstruction of 568 years for Hengduan Mountain was presented at the Hengduan Mountain in monsoonal Asia. Drought variations of the western and eastern parts of the central High Asia show different patterns and drought histories of the southern and northern portions of the monsoonal Asia show divergent patterns.The author used a tree-ring network of 64 chronologies in NW China and vicinity to reconstruct the leading drought variability of the western and eastern parts of central High Asia, including NW China, since 1587 and 1660. Meanwhile, the thesis conducted point-by-point precipitation reconstructions for the 26 stations in NW China. Based on the reconstructed precipitation dataset, singular value decomposition method was employed to study the key linkages between precipitation of NW China and sea surface temperatures in Pacific and Indian oceans.更多还原