单桩极限承载力时间效应估算方法比较

沉入饱和软土中的预制制桩的极限承载力随间歇期的增长而增大,这一现象虽已被工程界广泛认可,但至今仍然没有得到很好地解决。有效地确定单桩承载力随时间变化的规律对桩基础设计非常重要。人们提出了多种估算预制桩随时间变化的桩承载力的方法,但由于不同方法有各自的适用性和局限性,算出的结果有时差别很大,在使用时很难准确把握。首先分析了用于估算饱和软土中预制桩承载力随时间变化的几种方法：对数函数法、双曲函数法、人工神经网络法和基于超孔隙水压力消散的理论解析公式法。再以简洁性、理论性、适用性等为准则,结合工程实例,对以上几种方法进行比较,指出各自优缺点,推荐基于超孔隙水压力消散的简化解析方法来估算软土中预制桩承载力随时间变化的规律。     

中国土壤有效含水量分布

1IntroductionAvailable soil water capacity (ASWC) is the volume of soil water that should be available to plants. It is commonly estimated as the amount of water held between field capacity (FC) and permanent wilting point (PWP) with corrections for salin…     

A simple expression for the bulk field capacity of a sloping soil horizon

Field capacity is a commonly used soil parameter in surface water hydrological models, loosely defined as the moisture content of a soil after drainage. The most commonly applied expression for field capacity is defined as the remaining water in a vertical soil column subject to 1/3 atm. of pressure head. While this quantification is sufficient in some cases, the definition is not consistent with the use of bulk field capacity in calculations of lateral drainage from hillslopes, as required by some surface soil parameterizations, nor does it address additional complications arising from differences in soil texture or sample size. Here, a simple alternative expression for bulk field capacity in a sloping or vertical soil is derived directly from Richards equation with the use of the Brooks‐Corey characteristics. It is demonstrated that this expression is consistent with data acquired from vertical soil columns, but may be extended to additional situations commonly found in surface water models and land surface schemes. The calculation of bulk field capacity requires only the Brooks‐Corey pore size distribution index, soil air‐entry pressure, and hillslope length and slope, and may be considered a physically based alternative to pedotransfer function or lookup table approaches. Copyright © 2010 John Wiley & Sons Ltd and Crown in the right of Canada.     

Learning effects of interactive decision-making processes for climate change adaptation

Learning is gaining attention in relation to governance processes for contemporary environmental challenges; however, scholarship at the nexus of learning and environmental governance lacks clarity and understanding about how to define and measure learning, and the linkages between learning, social interactions, and environment. In response, this study aimed to advance and operationalize a typology of learning in an environmental governance context, and examined if a participatory decision-making process (adaptive co-management) for climate change adaptation fostered learning. Three types of learning were identified: cognitive learning, related to the acquisition of new or the structuring of existing knowledge; normative learning, which concerns a shift in viewpoints, values or paradigms, and relational learning, referring to an improved understanding of others’ mindsets, enhanced trust and ability to cooperate. A robust mixed methods approach with a focus on quantitative measures including concept map analysis, social network analysis, and self-reflective questions, was designed to gauge indicators for each learning type. A participatory decision-making process for climate change adaptation was initiated with stakeholders in the Niagara region, Canada. A pseudo-control group was used to minimize external contextual influences on results. Clear empirical evidence of cognitive and relational learning was gained; however, the results from normative learning measures were inconclusive. The learning typology and measurement method operationalized in this research advances previous treatments of learning in relation to participatory decision-making processes, and supports adaptive co-management as a governance strategy that fosters learning and adaptive capacity.     

Using land cover changes and demographic data to improve hydrological modeling in the Sahel

At the beginning of the drought in the Sahel in the 1970s and 1980s, rainfall decreased markedly, but runoff coefficients and in some cases, absolute runoff increased. This situation was due to the conversion of the land cover from natural vegetation with a low annual runoff coefficient, to cropland and bare soils, whose runoff coefficients are higher. Unless they are adapted, hydrological conceptual models, such as GR2M, are unable to reproduce this increase in runoff. Despite the varying environmental and climatic conditions of the West African Sahel, we show that it is possible to increase the performance of the GR2M model simulations by elaborating a time‐varying soil water holding capacity and to incorporate this value in the annual maximum amount of water to be stored in reservoir A of the model. We looked for interactions between climate, rural society, and the environment. These interactions drive land‐cover changes in the Sahel, which in turn drive the distribution of rainfall between infiltration, evaporation, and runoff and hence the water resources, which are vital in this region. We elaborated several time series of key indicators linked to these interactions. We then integrated these changes in the runoff conditions of the GR2M model through the maximum value of the reservoir capacity. We calculated annual values of water holding capacity using the annual values of four classes of land cover, natural vegetation, cultivated area, bare soil, and surface water. We then used the hydrological model with and without this time‐varying soil value of A and compared the performances of the model under the two scenarios. Whatever the calibration period used, the Nash–Sutcliffe index was always greater in the case of the time‐varying A time series.     

Spatial and temporal variability of canopy and forest floor interception in a beech forest

Depending on season, rainfall characteristics and tree species, interception amounts to 15–50% of total precipitation in a forest under temperate climates. Many studies have investigated the importance of interception of different tree species in all kinds of different climates. Often authors merely determine interception storage capacity of that specific species and the considered event, and only sometimes a distinction is made between foliated and non‐foliated trees. However, interception is highly variable in time and space. First, since potential evaporation is higher in summer, but secondly because the storage capacity has a seasonal pattern. Besides weather characteristics, such as wind and rain intensity, snow causes large variations in the maximum storage capacity. In an experimental beech plot in Luxembourg, we found storage capacity of canopy interception to show a clear seasonal pattern varying from 0·1 mm in winter to 1·2 mm in summer. The capacity of the forest floor appears to be rather constant over time at 1·8 mm. Both have a standard deviation as high as ± 100%. However, the process is not sensitive to this variability resulting only in 11% variation of evaporation estimates. Hence, the number of raindays and the potential evaporation are stronger driving factors on interception. Furthermore, the spatial correlation of the throughfall and infiltration has been investigated with semi‐variograms and time stability plots. Within 6–7 m distance, throughfall and infiltration are correlated and the general persistence is rather weak. Copyright © 2010 John Wiley & Sons, Ltd.     

“Caribou was the reason,and everything else happened after”: Effects of caribou declines on Inuit in Labrador,Canada

For many Indigenous Peoples in the Circumpolar North, cultural engagement and continuity across generations is directly related to relationships between and among people, animals, and landscapes. However, minimal research outlines the emotional responses and disruptions to culture and identity that are driven by ecological change, and the subsequent cultural dimensions of coping and adapting to this uncertainty. Through a case study that explores how caribou population declines and a caribou hunting ban are impacting Inuit in the Nunatsiavut and NunatuKavut regions of Labrador, Canada, this article examines the critical interplay between cultural continuity and adaptive capacity for responding to ecological uncertainty. More specifically, this study: 1) described the central role that caribou play for Inuit emotional wellness, identity, and cultural continuity; 2) explored how the rapid declines of caribou in Labrador are affecting Inuit emotional wellness, identity, and cultural continuity; and 3) characterized the ways in which Inuit are adapting to these emotio-social, cultural, and ecological changes. Drawing from an Inuit-led, multi-year, multi-media qualitative and visual media research program, data from video interviews (n = 84: Nunatsiavut region: n = 54; NunatuKavut region: n = 30) were analyzed using a video-based qualitative analysis, constant-comparative methods, and inductive qualitative approach. Results indicated that caribou are a foundational element for Inuit emotional wellness, identity, and cultural continuity. The changes in caribou populations are resulting in complex emotional responses, losses to cultural meaning and knowledge, and alterations to Inuit identities. The impacts on emotions, identity, and cultural continuity related to Inuit-caribou relations at an individual and collective level reflect the interconnections between cultural continuity and adaptive capacity that underlie the loss of this culturally important species. Though this research focuses on two Inuit groups and caribou in Labrador, the insights from these lived experiences highlight the ongoing cultural and identity consequences associated with species declines occurring globally.     

多源时相遥感影像数据耦合的水库库容曲线重构

遥感技术为库容曲线的重构带来了新思路,但仍存在多源遥感影像数据难以直接应用、水库批量面积提取效率低等问题,难以形成一套系统化、流程化的方法进行广泛应用。基于此,本文提出了多源时相遥感影像数据耦合的库容曲线重构方法,并重构了深圳市径心水库的水位-库容关系曲线。试验证明,重构后的库容曲线常水位区间的库容曲线偏离率在4.23%~11.5%之间,能够为径心水库的调度管理提供参考,同时对全国库容曲线无法及时重构的水库具有参考意义。     

Geographical imbalances and divides in the scientific production of climate change knowledge

Studies on scientific production of climate change knowledge show a geographical bias against the developing and more vulnerable regions of the world. If there is limited knowledge exchange between regions, this may deepen global knowledge divides and, thus, potentially hamper adaptive capacities. Consequently, there is a need to further understand this bias, and, particularly, link it with the exchange of knowledge across borders. We use a world-wide geographical distribution of author affiliations in >15,000 scientific climate change publications to show that (1) research production mainly takes place in richer, institutionally well-developed countries with cooler climates and high climate footprints, and (2) the network of author affiliations is structured into distinct modules of countries with strong common research interests, but with little knowledge exchange between modules. These modules are determined mainly by geographical proximity, common climates, and similar political and economic characteristics. This indicates that political-economic, social and educational-scientific initiatives targeted to enhance local research production and collaborations across geographical-climate module borders may help diminish global knowledge divides. We argue that this could strengthen adaptive capacity in the most vulnerable regions of the world.     

基于HWSD的流域栅格土壤水分常数估算

在科研及实践工作中往往需要大量的、空间分辨率较高的凋萎系数、田间持水量和饱和含水量数据,大规模布点测定这些土壤水分常数难度较大,需要探索估算这几种常用土壤水分常数的新方法。以黑龙江省呼兰河流域为例,采用DEM数据提取流域边界,应用提取后的流域DEM从世界土壤数据库(HWSD)中提取流域土壤的砂粒、粘粒百分含量及USDA土壤质地分类数据,再应用这三种土壤属性数据估算流域各栅格的凋萎系数、田间持水量和饱和含水量。研究结果表明:应用HWSD可以估算出呼兰河流域0~30cm和30~100cm两种土层的凋萎系数、田间持水量和饱和含水量,空间分辨率可达到30″,为获取较高分辨率及深土层的区域土壤水分常数提供了一种新方法。