黄土高原极端温度事件的时空变化

极端温度事件对农业生态系统有显著影响,其变化趋势需要进行评估。基于黄土高原50个站点的日序列最高和最低温度数据,经定义极端温度事件及其衡量指标(频率、强度、年极值和日温差)后,评价了黄土高原1961-2007年极端温度事件的空间分布和长期变化趋势。结果表明1,961-2007年黄土高原极端温度事件不同指标的空间分布有显著差异,基本上沿东南—西北方向呈梯度变化。多数站点极端温度事件的变化具有单调趋势,但趋势具有显著意义的站点数有很大差异,96%以上站点极端高(低)温事件的频率显著升高(降低);70%站点的日温差(46%降低和24%升高)和最低温度年极值的升高趋势具有显著性;约50%站点极端低温事件的强度和最高温度年极值的增加趋势显著;其他指标的显著性趋势较少。黄土高原极端温度事件对全球变暖的响应有其特殊性。     

北京极端天气事件及其与区域气候变化的联系

应用逐日观测资料分析了北京极端天气事件的变化及其与区域气候变暖的可能联系，得到了如下结论：（1）近30多年来高温和闷热事件在增加，低温、大风、雷暴和大雾事件在减少，暴雨和沙尘暴的出现频率无明显的变化。（2）高温、闷热、低温、大风、雷暴和大雾存在着较强的年际变化，但不具有明显的周期性特征，暴雨和沙尘暴事件分别存在10年和8～10年的主周期变化。（3）年平均气温和高温、闷热、低温、大风等极端事件之间存在着较强的相关性，这些极端天气事件的变化与区域气候变暖关系密切。     

极端气温对城市人群死亡的影响评估

利用北京心肺血管疾病研究所提供的1994-2000年北京城近郊区的七个监测点的以25-74岁人群为监测对象的25余万居民中全死因死亡事件监测数据、同期北京观象台的逐日气温观测数据、月平均气候资料，对极端气温对城市人群死亡的影响进行分析，得出对城市人群死亡影响的极端气温阈值及其长序列的时间线形变率，采用最优子集回归方法建立预测评估模型，根据气候模式对未来气候变化的预测结果，对未来北京城市人群死亡的影响进行定量评估。     

新疆极端水文事件年内分布的非均匀性

利用1901-2010年的资料,采用传统统计方法以及新引入的衡量年内分布情况的集中度、集中指数,对比分析了新疆极端水文事件的年内分布特征。分析发现,传统统计方法和集中度、集中指数得出的年内分布具有很好的一致性,是一种可靠的分析方法,今后可以借鉴使用。结果表明:新疆极端水文事件年内分布极不均匀,夏半年和夏季的集中指数较大,而冬半年和冬季的集中指数较小,即大部分地区极端水文事件主要发生在夏半年,冬半年发生相对较少,但北疆的阿勒泰地区冬半年极端水文事件较多;吐鲁番的极端水文事件年内分布非常集中,乌鲁木齐、奎屯—石河子、阿克苏地区次之,阿勒泰地区集中度最小。     

北京地区极端温度事件的变化趋势和年代际演变特征

利用北京地区20个气象观测站1978-2007年逐日平均温度资料,分析了近30年北京地区极端温度事件的变化趋势以及年代际空间演变特征。研究结果显示,北京观象台近30年的两次迁站对研究极端温度事件并无太大影响;近10年夏季显著的热岛效应,是城区极端高温事件发生频次明显高于其他地区的重要原因;尽管北京地区冬季平均温度的空间分布形态变化甚微,并始终存在着明显的热岛效应,但城区极端低温事件的发生频次有可能发生了与热岛效应无关的突变过程。     

吉林省夏季极端降水事件特征分析

利用吉林省46个气象站1961-2010年逐日降水资料,采用百分位定义极端事件阈值的方法,对吉林省极端降水事件的时空分布及变化趋势特征进行了分析。结果表明:(1)吉林省极端降水事件主要发生在夏季,其中5%的降水日数贡献了该季度25%～30%的降水量;夏季极端降水强度以通化地区最强、东部山区最弱,极端降水频率东部山区最大、西北部最小;(2)吉林省100mm以上的极端大暴雨天气也时有发生,通化地区南部发生几率最大,约为4～6 a一遇;中部一带约为8～10a一遇;西北平原区和东部山区出现大暴雨概率很小。(3)近50a吉林省夏季极端降水事件稍有增多的趋势,而强度变化趋势不明显,但存在明显的地域差别,西北部表现为频率减少、强度减弱,中部和东南部表现为频率增多、强度增强。(4)极端降水事件存在年代际差异,20世纪70年代极端降水频率最小,90年代极端降水强度最大,60年代初期极端降水强度存在由强转弱的突变。     

Population collapses in the pre-modern period: case study of the Fuping County,Northwest China

The pre-modern history of population change in the Fuping County (Shaanxi Province, China) during the Ming and Qing Dynasties (AD 1368–1911) was reconstructed using historical sources. The Fuping County experienced two major population collapses, i.e. the late Ming Dynasty (1550–1640s) and the 1860–1880s. The first one was caused by the great AD 1556 earthquake and the extreme droughts and warfare in the 1630–1640s. The second one was caused by warfare and extreme droughts. As a whole, natural disasters, including extreme drought and great earthquake, were the key direct causes of population collapse, and climatic cooling would be a potential indirect cause. It is very interesting that population collapses occurred almost synchronously in the Fuping County and whole China, and the trends of population change were also very similar. Climate–population relationship in China would be valid at finer geographic level, and climatic cooling could be a potential indirect cause of population collapse.     

1962～2012年西南地区极端温度事件时空变化特征

基于西南地区88站1962~2012年日气温数据,采用百分位阈值法定义极端温度事件,结合线性倾向率、Mann-Kendall秩次相关法、反距离加权插值法对其时空变化进行了分析。结果表明:极端温度指数存在明显的空间分布差异,暖日指数、暖夜指数、冷夜指数和年内日最低气温整体上均由东南向西北逐渐降低;霜冻天指数则由东南向西北部逐渐升高,西北部梯度变化明显;冷日指数和年内日最高气温呈马鞍状分布,较高值均在西南和东北部;因多数地区高温天数极少,故没有明显的梯度变化。霜冻天指数、冷夜指数和冷日指数减少趋势明显,分别为2.7、4.6和3.5d/10a;暖日指数和暖夜指数、年内日最低气温和最高气温均呈增加趋势,分别为3.6、4.9、0.4和0.1℃/10a;高温天指数变化不显著。整体上来看,西南地区极端高温事件和极端低温事件分别呈上升和下降趋势,但有部分区域呈相反变化趋势,体现出西南地区气候变化的独特性。     

Characteristics of pellets with immobilized activated sludge and its performance in increasing nitrification in sequencing batch reactors at low temperatures

Immobilized pellets obtained by means of entrapping activated sludge in waterborne polyurethane were successfully adapted in ammonium(NH_4~+–N)synthetic wastewater.Its physicochemical characteristics were determined using scanning electron microscope,pyrosequencing,and microelectrodes,and its influence on the nitrification process in sequencing batch reactors(SBRs)at low temperatures was evaluated.A large number of rod-shaped bacteria were observed on the surface of the immobilized pellet,in which Rudaea spp.(Xanthomonadaceae family)was an important bacterial component(23.44% of the total bacteria).The oxygen uptake rate of immobilized pellets reached 240.83±15.59 mg O_2/(L·hr),and the oxygen was primarily consumed by the bacteria on the pellet surfaces(0–600μm).The dosing of the pellets(30 m L/L)into an SBR significantly improved the nitrification efficiency at low temperatures of 7–11°C,achieving an average NH_4~+–N removal of 84.09%,which is higher than the removal of 67.46% observed for the control group.     

Modelling breakdown of industrial thermal insulation during fire exposure

The aging of many of the installations in the oil and gas industry may increase the likelihood of loss of containment of flammable substances, which could lead to major accidents. Flame temperatures in a typical hydrocarbon fire may reach 1100–1200 °C, which are associated with heat flux levels between 250 and 350 kW/m². To limit or delay the escalation of an initial fire, passive fire protection (PFP) can be an effective barrier. Additionally, both equipment and piping may require thermal insulation for heat or cold conservation. Previous studies have investigated whether thermal insulation alone may protect the equipment for a required time period, e.g., until adequate depressurization is achieved. The present study entails the development of a numerical model for predicting the heat transport through a multi-layer wall of a distillation column exposed to fire. The outer surface is covered by stainless-steel weather protective cladding, followed by PFP, thermal insulation, and finally an inner column of carbon steel of variable thicknesses. The model for the breakdown of thermal insulation is based on observed dimensional changes and independent measurements of the thermal conductivity of the insulation after heat treatment. The calculated temperature profiles of thermally insulated carbon steel during fire exposure are compared to fire test results for carbon steel with thicknesses of 16, 12, 6 and 3 mm. The model's predictions agree reasonably well with the experiments. The degradation of the thermal insulation at temperatures above 1100 °C limits its applicability as fire protection, especially for low carbon-steel thickness. However, the model predicts that adding a 10-mm layer of more heat-resistant insulation (PFP) inside the fire-exposed cladding may considerably extend the time to breakdown of the thermal insulation.