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71.
Climatic change through global warming and drought is a major issue for agricultural production. Most researchers who discuss
the effects of such changes on agriculture report estimated yield changes based on crop process models. However, studies focusing
on the impact of climatic change on agricultural product markets are very rare. This paper examines the relationship between
climatic change and world food markets, i.e., the supply and demand of crops, by using a stochastic version of a world food
model, the International Food and Agricultural Policy Simulation Model. The results suggest that variations in the production
of maize and soybeans in some major producing countries will be large, and variations in the producer prices of all crops
will increase. Countries that suffer higher price risk because of high sensitivity to temperature fluctuations may need to
consider changes in cropping patterns. 相似文献
72.
Elizabeth Ramlal Denys Yemshanov Glenn Fox Daniel McKenney 《Journal of environmental management》2009
This study explores the economic attractiveness of afforestation as a strategy for the joint production of fibre, carbon storage and biosolids (treated municipal sewage sludge) disposal for municipalities in Southern and Central Ontario, Canada. We use a spatial, stochastic model, the Canadian Forest Service Afforestation Feasibility Model (CFS-AFM), to simulate a range of spatial biosolids application scenarios in hybrid poplar afforestation projects. Results suggest that such joint afforestation strategies could be financially attractive. Significant cost savings can be expected through decreases in transportation distances and avoided waste disposal fees. Sensitivity analysis is used to examine the effects of variations in critical model parameters on net present values. Our findings indicate that waste disposal savings from application of biosolids on hybrid poplar plantations combined with incentives for landowners to sequester carbon can easily compete with agricultural land rental values in some regions of Ontario. Social acceptance of this kind of activity, however, may be an impediment to adoption. 相似文献
73.
We develop a reserve design strategy to maximize the probability of species persistence predicted by a stochastic, individual-based,
metapopulation model. Because the population model does not fit exact optimization procedures, our strategy involves deriving
promising solutions from theory, obtaining promising solutions from a simulation optimization heuristic, and determining the
best of the promising solutions using a multiple-comparison statistical test. We use the strategy to address a problem of
allocating limited resources to new and existing reserves. The best reserve design depends on emigration, dispersal mortality,
and probabilities of movement between reserves. When movement probabilities are symmetric, the best design is to expand a
subset of reserves to equal size to exhaust the habitat budget. When movement probabilities are not symmetric, the best design
does not expand reserves to equal size and is strongly affected by movement probabilities and emigration rates. We use commercial
simulation software to obtain our results. 相似文献
74.
75.
Inexact multistage stochastic integer programming for water resources management under uncertainty 总被引:8,自引:0,他引:8
In this study, an inexact multistage stochastic integer programming (IMSIP) method is developed for water resources management under uncertainty. This method incorporates techniques of inexact optimization and multistage stochastic programming within an integer programming framework. It can deal with uncertainties expressed as both probabilities and discrete intervals, and reflect the dynamics in terms of decisions for water allocation through transactions at discrete points of a complete scenario set over a multistage context. Moreover, the IMSIP can facilitate analyses of the multiple policy scenarios that are associated with economic penalties when the promised targets are violated as well as the economies-of-scale in the costs for surplus water diversion. A case study is provided for demonstrating the applicability of the developed methodology. The results indicate that reasonable solutions have been generated for both binary and continuous variables. For all scenarios under consideration, corrective actions can be undertaken dynamically under various pre-regulated policies and can thus help minimize the penalties and costs. The IMSIP can help water resources managers to identify desired system designs against water shortage and for flood control with maximized economic benefit and minimized system-failure risk. 相似文献
76.
Realistic models of contaminant transport in groundwater demand detailed characterization of the spatial distribution of subsurface hydraulic properties, while at the same time programmatic constraints may limit collection of pertinent hydraulic data. Fortunately, alternate forms of data can be used to improve characterization of spatial variability. We utilize a methodology that augments sparse hydraulic information (hard data) with more widely available hydrogeologic information to generate equiprobable maps of hydrogeologic properties that incorporate patterns of connected permeable zones. Geophysical and lithologic logs are used to identify hydrogeologic categories and to condition stochastic simulations using Sequential Indicator Simulation (SIS). The resulting maps are populated with hydraulic conductivity values using field data and Sequential Gaussian Simulation (SGS). Maps of subsurface hydrogeologic heterogeneity are generated for the purpose of examining groundwater flow and transport processes at the Faultless underground nuclear test, Central Nevada Test Area (CNTA), through large-scale, three-dimensional numerical modeling. The maps provide the basis for simulation of groundwater flow, while transport of radionuclides from the nuclear cavity is modeled using particle tracking methods. Sensitivity analyses focus on model parameters that are most likely to reduce the long travel times observed in the base case. The methods employed in this study have improved our understanding of the spatial distribution of preferential flowpaths at this site and provided the critical foundation on which to build models of groundwater flow and transport. The results emphasize that the impacts of uncertainty in hydraulic and chemical parameters are dependent on the radioactive decay of specific species, with rapid decay magnifying the effects of parameters that change travel time. 相似文献
77.
防灾工程投资的动态评估 总被引:1,自引:0,他引:1
本文以动态的观点,根据灾害发生的不确定性以及未来各时间内,净现金流量发生的不确定性,将整个现金流量过程看作是一个随同过程,提出计算模型,达到相对正确地、动态地估算出平均防灾工程投资折现值,从而对防灾工程投资的经济效益作出正确评价。 相似文献
78.
隧道地层变位的可靠性分析 总被引:3,自引:1,他引:3
分析了隧道与围岩设计中的不确定性因素 ,指出由于隧道及岩土参数分布的随机性 ,地层变位具有不确定性。运用ANSYS有限元程序建立隧道地层变位的计算模型 ,进行数值模拟并取得地层变位的原始数据。在此基础上把主要影响因素视为随机输入变量 ,地层变位为随机输出变量 ,采用蒙特卡洛方法模拟出地层位移的统计值 ,进而计算出地层变位的可靠指标与失效概率 ,并通过相关系数矩阵和概率灵敏度图分析了随机输入参数对地层变位的影响 ,为隧道地层变位的可靠性分析提供了一种新的途径。 相似文献
79.
An individual method cannot achieve the optimum risk-assessment result in the worksites, and future perspectives should focus on the parallel application of a deterministic approach with a stochastic approach. In particular, the risk analysis and assessment techniques of the deterministic (DET) approach are classified into three main categories: (a) the qualitative, (b) the quantitative, and (c) the hybrid techniques (qualitative-quantitative, semi-quantitative). Furthermore, the stochastic (STO) approach includes the classic statistical approach (CSA) and the accident forecasting modeling (AFM). The objective of this paper is triple: (a) the presentation and classification of the main risk analysis and risk assessment methods and techniques of the deterministic approach and the stochastic approach as well, (b) the development and presentation of a new alternative risk assessment framework (called as STODET) including a stochastic and a deterministic process, and (c) the application of STODET in the Greek Public Power Corporation (PPC) by using occupational accidents that have been recorded, during the 17-year period of 1993-2009. In particular, the STODET application proves that required actions (or suppressive measures) are essential and must be taken in a medium-term period (1 working year) for abolishing the hazard sources. 相似文献
80.
A key obstacle to practical application of mechanism design theory to regulation is the difficulty of obtaining consistent beliefs regarding information that theoretical models assume to be commonly held. This article presents a solution to this problem by developing an easily implemented empirical methodology with which the government can use available data to develop beliefs regarding the technology and distribution of types in a regulated sector characterized by hidden information. Results are used to calibrate a second-best land conservation mechanism and evaluate its cost relative to simpler alternatives. 相似文献