土壤与全球环境变化

本文着重论述了“土壤变化”与“全球气候变化”之间的相互作用。土壤圈通过其内部一系列的理化、生化变化及土地利用变化等,产生CO_2、CH_4、N_2O等“温室效应”气体特别是CH_4和N_2O向大气的排放,对“全球气候变化”产生重要的影响,而全球气候变暖又会引起土壤沙漠化、酸化、盐渍化等退化过程的进一步加剧,严重改变人类生存的环境。加强科学宣传,提高全球民众环境意识,加强科学研究与监测,提出相应措施,是适应或改变上述全球变化的重要战略对策。     

THE CHANCE A FLOOD WILL BE EXCEEDED IN A PERIOD OF YEARS1

ABSTRACT. Much has been written about the chance that a hydrologic event, such as a flood peak of a given size or greater, will occur during a given period of years. Four variables are involved, and any one of the four can be the dependent variable: (1) the probability of encountering such an event in a single year, (2) the probability of encountering one or several of these events in a period of years, (3) the least number of times of encountering the event in that period of years, and (4) the number of years in the period involved. Most of these problems are not difficult to solve, but they are tedious to calculate, not well understood, and consequently seldom used in water resources planning and development. The most popular approach is based on the binomial distribution. Graphical procedures similar to those developed by Riggs [1961] were further elaborated and are presented here with illustrative examples to facilitate their use in solving the many related problems. The confidence that one can place in these probability estimates is also explained and illustrated by tables and further examples. To help assure proper use of these methods, commonly used terms such as “recurrence interval” and “partial duration series” are discussed. No new theory is developed: at issue is a deeper understanding of the significance of design levels and their ease of computation.     

The role of electricity in sustainable development

Current projections estimating world population growth read in conjunction with corresponding projections of increased world energy consumption, point to electricity as the cleaner fuel of the future, especially because of its high efficiency and low levels of pollution. Due mostly to the fact that the electrical end-use devices are considerably more efficient than those using other forms of energy, most developed countries show decreasing curves of energy intensity as technologies become more sophisticated and shift over to increased reliance on electricity. It is therefore argued in this article that a gradual shift away from fossil fuels to electricity is a promising possibility to bring down global air pollution and emissions of greenhouse gases to acceptable levels. Examples are given of greater efficiency achieved by electrification. Overall gains in energy efficiency from the change over from fossil fuels to electricity, are possible even in situations where the electricity is generated by fossil fuel combustion, despite the loss of primary energy in the conversion process. The article also presents electricity generating projects designed for developing countries and countries with economies in transition. The generation of electricity from the combustion of renewable sources (biomass waste), fossil fuels, and other innovative methods are outlined.     

interactions amongst policies designed to resolve individual air issues

Six air issues are currently on science and policy agendas in Canadaand elsewhere. These are climate change, stratospheric ozone depletion(increased UV-B radiation), acidic deposition, SMOG (increasedground-level ozone), suspended particulate matter, and hazardous airpollutants. Atmospheric scientists and decision makers have largelyaddressed these issues individually resulting in single-issue policies. However, it is now recognized that these issues are inter-related, andthey may interact to cause negative as well as some beneficial effects,not only on the state of the atmosphere but also on societal andecological systems. This paper illustrates through several examples theatmospheric dysfunction caused by the linkages among the six airissues. It also points to potentially conflicting policies arising from thesingle-issue approach, and it emphasizes the need for better integrationof air issues. The linkages are summarized qualitatively in Table I.     

Environmental degradation and remediation: is economics part of the problem?

It is argued that standard environmental economic and 'ecological economics', have the same fundamentals of valuation in terms of money, based on a demand curve derived from utilitymaximization. But this approach leads to three different measuresof value. An invariant measure of value exists only if the consumer has 'homothetic preferences'. In order to obtain a numerical estimate of value, specific functional forms are necessary, but typically these estimates do not converge. This is due to the fact that the underlying economic model is not structurally stable.According to neoclassical economics, any environmental remediation can be justified only in terms of increases in consumer satisfaction, balancing marginal gains against marginal costs. It is not surprising that the optimal policy obtained fromthis approach suggests only small reductions in greenhouse gases.We show that a unidimensional metric of consumer's utility measured in dollar terms can only trivialize the problem of global climate change.     

THE EFFECT OF EL NIÑO-RELATED DROUGHT ON THE RECOVERY OF ACIDIFIED LAKES

Although SO₂ emissions and deposition rates havedeclined substantially since the implementation of sulphuremission control programmes in North America [1], recovery(measured as decreases in concentrations) of affected lakes in central Ontario has been much less substantial thananticipated based on the decrease in deposition. The slowrecovery is attributed to the reoxidation and release of storedsulphur in catchments. Reduced sulphur retained in previousyears when sulphur deposition was higher is exposed to air andoxidized during severe droughts, then exported duringsubsequent wet periods. Elevated stream concentrations and export rates occur in the autumns of yearswith prolonged severe droughts, particularly in catchments withextensive wetlands. Drought in our study catchments occurred inyears following strong El Niño events. When the SouthernOscillation Index (SOI) was strongly negative (1976–77, 1982–83,1986–87, 1991–92, 1993–94) the frequency of occurrence ofdrought the following summer in small catchments with shallowoverburden was extremely high. A lakes rate of recovery fromacidification depends upon the amount of excess reduced Sthat has been stored in anoxic zones in the catchment (largely afunction of the extent of wetlands) during years of elevated Sdeposition rates, and the frequency and severity of droughts. Iflong-term changes in global or regional climate alter thefrequency or magnitude of El Niño-related droughts, therecovery of acidified lakes will be affected.     

Spatial Patterns of Soil Moisture as Affected by Shrubs, in Different Climatic Conditions

At three study sites, representing Mediterranean, semi-aridand mildly-arid climatic conditions, the effect of shrubs onthe spatial patterns of soil moisture was studied. At eachsite soil moisture was measured, on hillslopes, at thevicinity of 8 shrubs. For each shrub the measurements havebeen taken at 3 microenvironments, i.e. under the shrub (US),at the margins of shrub (MS) and between shrubs (BS). At themicroenvironments US and MS the measurements were taken at 3 directions: upslope, downslope and sideslope of the shrubs. At all sampling points soil samples were taken from 3 depths: 0–2, 2–5 and 5–10 cm. In addition, rock fragments cover percentage near the shrubs was determined. A soil moisture pattern was found, around each shrub,which is composed of a radial gradient and a downslope gradient. The radial gradient is expressed by soil moisture decreasingfrom the US microenvironment, in all directions, through the MS towards the BS microenvironment. The US microenvironmenthas a `spatial advantage' of higher soil moisture content dueto (1) relatively higher infiltration rate, (2) capture overlandflow from the BS area upslope that shrub and (3) low evaporationrate because of the shading effect.The downslope gradient is expressed by decreasing soil moisturefrom the upslope direction of each shrub (MS and US microenvironments) towards the downslope direction of that shrub (MS and US microenvironments, respectively). Thisgradient is controlled by the relatively high content of rockfragments near the shrubs at their upslope direction. Suchrock fragments spatial distribution is attributed to (1) thedetachment and transport of rock fragments by sheep and goatstrampling and (2) the effect of shrub on the continuity ofoverland flow and sediment transport. The effect of rockfragments is similar to that of shrubs regarding increasinginfiltration and decreasing evaporation rate. The relativelyhigh soil moisture at the upslope direction of each shrubenhances annuals growth producing a positive feedback loop:soil moisture – annuals growth – trampling. This sequencemaintains the typical rock fragments spatial organization andcontributes to the sustainability of the grazing system.At all the study sites at the US microenvironment there isa trend of decreasing soil moisture with increasing soildepth. At microenvironments MS and BS soil moisture increaseswith soil depth.The results are of great relevance for rehabilitationstrategies as they suggest that in order to combatdesertification in degraded semi-arid and mildly-arid areas,where the main land use is grazing, both shrubs and rockfragment should be kept at their present spatial distribution.     

2000—2015年青藏高原植被NPP时空变化格局及其对气候变化的响应

全球变化背景下,青藏高原作为我国乃至全球气候变化的“天然实验室”,植被生态系统发生了深刻变化。引入重心模型等方法分析和探讨2000—2015年青藏高原植被NPP时空变化格局及其驱动机理,并定量区分NPP变化过程中气候变化和人类活动的相对作用。研究发现：（1）2000—2015年,青藏高原植被NPP年均值总体上呈现从东南向西北递减的趋势。在年际变化方面,近16年植被NPP呈现波动上升趋势,其中在2005年出现上升陡坡,并在2005—2015年表现为高位波动的态势。（2）青藏高原植被NPP增加区（变化率>10%）主要集中于三江源地区、横断山区北部、雅鲁藏布江中下游以及那曲地区的中东部,而植被NPP减小区（变化率<-10%）则主要分布于雅鲁藏布江上游和阿里高原。（3）近16年青藏高原植被NPP重心总体向西南方向移动,表明西南部植被NPP在增量和增速上大于东北部。（4）青藏高原植被NPP与气候因子相关性的地区差异显著,其中植被NPP与降水显著相关的区域主要位于青藏高原中部、青藏高原东南部及雅鲁藏布江流域中下游,而植被NPP与气温显著相关的区域主要位于藏南地区、横断山区北部、青藏高原中部和北部。（5）气候变化和人类活动在青藏高原植被NPP变化过程中的相对作用存在显著的时空差异性,在空间上呈现“四线—五区”的格局。研究成果能够为揭示青藏高原区域生态系统对全球变化的响应机制提供理论和方法支撑。     

全球能源安全的格局演变与地缘博弈

受经济全球化影响,国家能源安全问题的国际化趋势日益突出。21世纪以来,伴随世界多极化加速发展,世界能源安全格局演变特征及其驱动机制成为能源地缘政治研究的关键问题之一。基于这一认识,对2000年以来全球124个国家能源安全状态进行了系统评价,揭示了世界能源安全空间格局的演变特征及主要形成机制,并提出了未来能源地缘政治的博弈焦点。结果显示：（1）自21世纪初以来,全球能源安全格局演变整体上不断优化,但呈现出明显的阶段性特征,即2010年以来,全球能源安全格局优化趋势更为显著。（2）世界能源安全格局与国际地缘秩序区划基本吻合,即能源安全型国家集中分布在西欧和北美经济发达地区,较安全型国家主要分布在中欧、拉丁美洲以及亚洲高收入地区,过渡型国家主要分布在中东、东南欧以及东亚等能源体系亟需转型的地区,而较危险和危险型国家集中分布在南亚以及非洲经济欠发达地区。（3）近20年以来,世界能源安全水平显著提升主要得益于发达经济体能源使用安全维度的良好表现,而发展中国家由于创新能力较低、生产力较落后、居民可支配收入较少,其能源安全水平提升空间较小。（4）当前及今后一段时期内,全球能源安全格局将受到中美关系变化的冲击、能源转型的胁迫以及政治环境不确定性的影响。     

公共大空间建筑生化恐怖模式和通风技术分析

公共大空间建筑生化恐怖模式主要有制造火灾产生毒性气体、爆炸毒气弹分散毒性物质和人工直接布洒毒性物质。分析表明:火灾烟气受热浮力作用,在建筑物上部出现明显的烟气层,采用自然或机械排烟能有效地减缓或控制烟气层下降;爆炸分散毒性物质,除了爆炸点周边区域外,毒气扩散受热气流诱导,以及浓度差引起的运动;不考虑室内对流气流的影响,人工布洒毒性物质产生的毒性气体,其扩散主要是由浓度差引起的。不同类型恐怖袭击产生的毒性气体受室内对流气流的控制,合适的通风方式能够控制毒性气体的扩散和输运过程。但能否采用某一形式的通风系统兼备防范不同类型的恐怖袭击,需要对通风系统的通风量、气流组织和控制方式做更深入的研究。