Response of tree growth to a changing climate in boreal central Canada: A comparison of empirical,process-based,and hybrid modelling approaches

The impact of 2 × CO₂ driven climate change on radial growth of boreal tree species Pinus banksiana Lamb., Populus tremuloides Michx. and Picea mariana (Mill.) BSP growing in the Duck Mountain Provincial Forest of Manitoba (DMPF), Canada, is simulated using empirical and process-based model approaches. First, empirical relationships between growth and climate are developed. Stepwise multiple-regression models are conducted between tree-ring growth increments (TRGI) and monthly drought, precipitation and temperature series. Predictive skills are tested using a calibration–verification scheme. The established relationships are then transferred to climates driven by 1× and 2 × CO₂ scenarios using outputs from the Canadian second-generation coupled global climate model. Second, empirical results are contrasted with process-based projections of net primary productivity allocated to stem development (NPP_s). At the finest scale, a leaf-level model of photosynthesis is used to simulate canopy properties per species and their interaction with the variability in radiation, temperature and vapour pressure deficit. Then, a top-down plot-level model of forest productivity is used to simulate landscape-level productivity by capturing the between-stand variability in forest cover. Results show that the predicted TRGI from the empirical models account for up to 56.3% of the variance in the observed TRGI over the period 1912–1999. Under a 2 × CO₂ scenario, the predicted impact of climate change is a radial growth decline for all three species under study. However, projections obtained from the process-based model suggest that an increasing growing season length in a changing climate could counteract and potentially overwhelm the negative influence of increased drought stress. The divergence between TRGI and NPP_s simulations likely resulted, among others, from assumptions about soil water holding capacity and from calibration of variables affecting gross primary productivity. An attempt was therefore made to bridge the gap between the two modelling approaches by using physiological variables as TRGI predictors. Results obtained in this manner are similar to those obtained using climate variables, and suggest that the positive effect of increasing growing season length would be counteracted by increasing summer temperatures. Notwithstanding uncertainties in these simulations (CO₂ fertilization effect, feedback from disturbance regimes, phenology of species, and uncertainties in future CO₂ emissions), a decrease in forest productivity with climate change should be considered as a plausible scenario in sustainable forest management planning of the DMPF.     

长沙对外贸易发展的现状及其对经济发展的影响

利用1998年到2006年长沙对外贸易的数据分析了长沙对外贸易发展的现状,结果表明长沙近几年对外贸易总体上呈不断增长趋势、贸易结构不断优化;同时对外贸易推动了长沙经济增长、技术进步、结构调整和竞争力的提升,但长沙对外贸易的规模偏小、增长速度偏低、对长沙经济增长的拉动作用小.长沙作为中部省会城市,其外贸发展情况必然带有整个中西部地区外贸的一些共性,对其他中部地区外贸研究具有一定参考价值.表2,参5.     

有限供水条件下农田灌溉时量优化——以河北省运东地区为例

本文探讨了灌溉水源限定条件下,农田灌溉时量优化计算方法,并以河北省运东地区3种主要作物为例进行了系统演算。从计算结果及其分析看,时量优化的经济效益明显,时量优化模型作为一种计算方法亦具有一定的实用意义。     

Dynamic risk assessment using failure assessment and Bayesian theory

To ensure the safety of a process system, engineers use different methods to identify the potential hazards that may cause severe consequences. One of the most popular methods used is quantitative risk assessment (QRA) which quantifies the risk associated with a particular process activity. One of QRA's major disadvantages is its inability to update risk during the life of a process. As the process operates, abnormal events will result in incidents and near misses. These events are often called accident precursors. A conventional QRA process is unable to use the accident precursor information to revise the risk profile. To overcome this, a methodology has been proposed based on the work of Meel and Seider (2006). Similar to Meel and Seider (2006) work, this methodology uses Bayesian theory to update the likelihood of the event occurrence and also failure probability of the safety system. In this paper the proposed methodology is outlined and its application is demonstrated using a simple case study. First, potential accident scenarios are identified and represented in terms of an event tree, next, using the event tree and available failure data end-state probabilities are estimated. Subsequently, using the available accident precursor data, safety system failure likelihood and event tree end-state probabilities are revised. The methodology has been simulated using deterministic (point value) as well as probabilistic approach. This Methodology is applied to a case study demonstrating a storage tank containing highly hazardous chemicals. The comparison between conventional QRA and the results from dynamic failure assessment approach shows the significant deviation in system failure frequency throughout the life time of the process unit.     

基于故障树与贝叶斯网络的钻井井塌事故的定量分析

井塌事故在钻井过程极其常见,由于钻井液、井身结构等设计不合理,以及钻井过程的误操作均会造成井塌的发生,其后果主要是造成卡钻、卡套管等事故,严重时造成井眼毁坏。为了对井塌事故进行危险性分析,采用贝叶斯网络与故障树相结合的方法,避免传统故障树方法的局限性。首先对井塌事故的所有危险因素进行辨识建立故障树,然后将故障树转化为贝叶斯网络,建立条件概率表,运用贝叶斯网络的推理能力对井塌事故进行危险性分析。对井塌事故各基本事件概率分布的计算分析结果表明,考虑事件的多态性,综合利用故障树分析法和贝叶斯网络法能有效提高井塌事故分析的有效性,推算出井塌事故概率分布更为准确。     

基于MODIS NPP的2006—2015年三江源区产草量时空变化研究

草地既是高原地区重要的生态屏障,也是维系当地人民生产生活的自然资源,准确估算本区域的产草量,可为区域资源开发利用、社会经济可持续发展决策提供科学参考。论文基于MODIS遥感影像获得不同分辨率的NDVI、EVI和NPP产品,结合三江源区监测点的产草量地面实测数据,利用统计分析方法分别建立多种产草量遥感估算模型。利用择优选取的估产模型进行区域适用性评价和模型反演,研究三江源区产草量在2006—2015年的时空分布情况。研究结果表明,基于MOD17A2H NPP的一元线性模型的估算精度相对较高,三江源区的产草量（单产）呈东多西少、自东南向西北逐渐减少的空间分布特点。2006—2013年的产草量（总量）整体呈上升趋势,2013年的产草量（总量）达到3 869.43×10⁴ t,产草量（总量）自2014年开始降低,2015产草量（总量）为2 069.07×10⁴ t。     

浐河、灞河硝酸盐端元贡献比例——基于硝酸盐氮、氧同位素研究

近年来,河流氮污染一直是生物地球化学领域研究的热点问题。然而,识别水体硝酸盐来源、端元贡献比例及其在水体中存在生物转化(硝化、反硝化)过程,仍旧是氮循环研究的难点问题。本研究选取流经西安市的两条河流——浐河和灞河,测定其河水溶解态硝酸盐氮、氧同位素组成,并结合Bayesian同位素混合模型,有效识别了两条河流从源头到汇入渭河河口处,氮素来源的变化,同时,定量分析了其贡献比例的变化。结果显示,河流源头附近,土壤有机氮是河流硝酸盐主要来源,其贡献比例接近30%;河流中游,由于沿河农业活动的增加,同位素指示河流硝酸盐主要来源转化为化学肥料,其贡献比例接近25%;河流下游,由于城市用水的汇入,硝酸盐氮、氧同位素值偏正,主要位于污水及粪肥区间,指示硝酸盐含量较高的生活污水及工业废水的输入,其贡献比例能达到30%以上。通过本研究,研究者定性及半定量的区分和浐河、灞河氮素来源,为今后有效控制氮污染提供了理论基础。     

贵州典型森林群落植物冠层叶片遭受酸雨直接伤害的模拟实验与效应分析

在贵州龙里地区开展降雨连续监测,依据监测结果,配置不同pH值梯度的模拟酸雨;选择杨梅、油茶等10种贵州典型森林群落优势种,对植物叶片开展模拟酸雨喷淋试验;并利用便携式光合仪LI-6400观测喷淋前后叶片的光合作用,研究酸雨对贵州典型森林群落植物叶片的直接伤害作用.实验结果显示:①pH值5.0和4.0的模拟酸雨基本不会影响供试树种冠层叶片的光合作用;pH值3.0的模拟酸雨使小果红椿、枫树冠层叶片的净光合作用速率不同程度地升高,升高率为11.03%和0.62%,其他树种效果不明显;②pH值2.0的模拟酸雨使供试树种冠层叶片的净光合作用速率降低,其中小果红椿、枫树、白栗和香叶树尤为明显,降低率为28.32%、30.32%、12.21%和11.37%;pH值2.0的模拟酸雨使小果红椿叶片出现可见直接伤害,叶缘和脉间出现黄白色斑点,有穿孔,其他树种未发现可见直接伤害症状.研究表明,研究区典型森林群落植物叶片出现可见直接伤害的酸雨pH值阈值在2.0～3.0之间;同时,在酸雨对叶片造成可见直接伤害之前,存在隐性直接伤害,对叶片造成隐性直接伤害的酸雨pH值阈值为3.0.依据试验结果,从研究区监测数据分析,目前酸雨对该区植物冠层叶片的直接伤害有限.     

A new approach to estimate nuclide ratios from measurements with activities close to background

Measurements of low-level radioactivity often give results of the order of the detection limit. For many applications, interest is not only in estimating activity concentrations of a single radioactive isotope, but focuses on multi-isotope analyses, which often enable inference on the source of the activity detected (e.g. from activity ratios). Obviously, such conclusions become questionable if the measurement merely gives a detection limit for a specific isotope. This is particularly relevant if the presence of an isotope, which shows a low signal only (e.g. due to a short half-life or a small transition probability), is crucial for gaining the information of interest.     

2011-2013年中国雾霾易发生期间API的分布格局

以2011-2013年每年的1-3月和10-12月的中国120个城市逐日空气污染指数(API)数据为基础,通过选取最优的空间插值方法获得雾霾易发生期间每月的API空间分布;采用面向对象的分形网络演化算法对API分布图进行图像分割,获取"污染场"基元,通过G*指数的空间聚集分析提取"污染岛"范围;构建城市污染效应比例指数来反映污染效应的时空变化趋势;利用小波变换分析城市大气污染时间序列的多尺度变化特征。结果表明:近3年来雾霾易发生期间API空间分布的高值区域面积呈现不断增大的态势,京津冀、山东半岛、长三角等地污染岛分布面积较大;在时间尺度上,全国七大地理分区的API强度呈现出一定的周期性,污染强度虽未表现出明显的时间差异,但1-3月西部的污染大于东部,10-12月北方的污染大于南方。