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Research questions at the regional, national and global scales frequently require the upscaling of existing models. At large scales, simple model aggregation may have a prohibitive computational cost and lead to over-detailed problem representation. Methods that guide model simplification and revision have the potential to support the choice of the appropriate level of detail or heterogeneity within upscaled models. Efficient upscaling will retain only the heterogeneity that contributes to accurate aggregated results. This approach to model revision is challenging, because automatic generation of alternative models is difficult and the set of possible revised models is very large. In the case where simplification alone is considered, there are at least n2−1 possible simplified models where n is the number of model variables. Even with the availability of High Performance Computing, it is not possible to evaluate every possible simplified model if the number of model variables is greater than roughly 35. To address these issues, we propose a method that extends an existing procedure for simplifying and aggregating mechanistic models based on replacing model variables with constants. The method generates simplified models by selectively aggregating existing model variables, retaining existing model structure while reducing the size of the set of possible models and ordering them into a search tree. The tree is then searched selectively. We illustrate the method using a catchment scale optimization model with c. 50,000 variables (Farm-adapt) in the context of adaptation to climatic change. The method was successful in identifying redundant model variables and an adequate model 10% smaller than the original model. We discuss how the procedure can be extended to other large models and compare the method to those proposed by others. We conclude by urging model developers to regard their models as a starting point and to consider the need for alternative models during model development. 相似文献
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Oluyede Clifford Ajayi Festus K. Akinnifesi Gudeta Sileshi Sebastian Chakeredza 《Natural resources forum》2007,31(4):306-317
Low soil fertility is one of the most important biophysical constraints to increasing agricultural productivity in sub‐Saharan Africa. Several renewable soil fertility replenishment (RSFR) technologies that are based on nutrient re‐cycling principles have been developed in southern Africa. Some success stories have been recorded (e.g. nitrogen‐fixing legumes), but the adoption of RSFR technologies has generally lagged behind scientific advances thereby reducing the potential impacts of the technologies. This paper describes the major RSFR technologies being promoted in the region, synthesizes available information regarding their adoption by farmers, and identifies the challenges, key lessons learnt and the way forward for up‐scaling RSFR technologies in the region. The review indicated that farmer uptake of RSFR technologies depends on several factors that can be grouped into broad categories: technology‐specific (e.g. soil type, management regime), household‐specific (e.g. farmer perceptions, resource endowment, household size), policy and institutions context within which RSFR is disseminated (inputs and output prices, land tenure and property rights), and geo‐spatial (performance of species across different bio‐physical conditions, location of village). Adoption of RSFR technologies can be enhanced by targeting them to their biophysical and social niches, facilitating appropriate policy and institutional contexts for dissemination, understanding the broader context and dynamics of the adoption process, a paradigm shift in the approach to the dissemination of RSFR (e.g. expanding RSFR to high value crop systems, exploring synergy with inorganic fertilizer) and, targeted incentive systems that encourage farmers to take cognizance of natural resource implications when making agricultural production decisions. 相似文献
34.
风电场在其建设及运行期间,会对周边的生态环境造成一定影响。文章具体以喀左县双庙风电场建设为例,探讨风电场的建设期和运营期对周边生态环境产生的影响,同时提出了风电场生态环境恢复的具体方法和措施。为风电场的生态环境保护提供借鉴。 相似文献
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I. V. Emelyanova G. E. Donald D. J. Miron D. A. Henry M. G. Garner 《Environmental Modeling and Assessment》2009,14(4):449-465
A probabilistic Bayesian method called weights of evidence (WofE) was used to develop a synthetic dataset of cattle farm locations at a national scale across Australia. The synthetic
dataset was required for the modelling of livestock movements with a view to assessing biosecurity implications. The WofE method is based on the analysis of spatial relationships between evidential patterns with respect to an event, such
as the actual location of a farm. The evidential patterns of cattle farms were derived from maps of land use, land tenure,
drainage systems, roads, settlements and long-term averaged rainfall. These evidential patterns were used for delineating
and ranking land areas suitable for cattle farming. For each evidential pattern statistics such as a positive weight, a negative weight and a contrast were calculated for estimating the degree of correlation between the evidential patterns and known farm locations. The integrated
evidential patterns of known farms were then used for estimating posterior probabilities and splitting land into five different
classes according to its suitability for farming.
相似文献
I. V. EmelyanovaEmail: |
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Drouet JL Capian N Fiorelli JL Blanfort V Capitaine M Duretz S Gabrielle B Martin R Lardy R Cellier P Soussana JF 《Environmental pollution (Barking, Essex : 1987)》2011,159(11):3156-3161
Modelling complex systems such as farms often requires quantification of a large number of input factors. Sensitivity analyses are useful to reduce the number of input factors that are required to be measured or estimated accurately. Three methods of sensitivity analysis (the Morris method, the rank regression and correlation method and the Extended Fourier Amplitude Sensitivity Test method) were compared in the case of the CERES-EGC model applied to crops of a dairy farm. The qualitative Morris method provided a screening of the input factors. The two other quantitative methods were used to investigate more thoroughly the effects of input factors on output variables. Despite differences in terms of concepts and assumptions, the three methods provided similar results. Among the 44 factors under study, N2O emissions were mainly sensitive to the fraction of N2O emitted during denitrification, the maximum rate of nitrification, the soil bulk density and the cropland area. 相似文献
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Kathleen F. Carlson Author Vitae Susan G. Gerberich Author Vitae Author Vitae Ann S. Masten Author Vitae Author Vitae John M. Shutske Author Vitae Author Vitae Colleen M. Renier Author Vitae 《Journal of Safety Research》2009,40(2):97-103
Problem
Children on family agricultural operations have high risk of injury. The association between children's behavioral traits and their risk of injury is not well understood.Method
Data from the Regional Rural Injury Study-II were used to assess behavioral risk factors for injury to children ages six to < 20 years. A total of 379 injury events (cases) and 1,562 randomly selected controls were identified. Adjusted odds ratios (OR) and 95% confidence intervals (CI), calculated using logistic regression, were used to estimate injury risk in reference to behavioral traits.Results
Injury risks were greater for children with high levels of depressive symptoms (OR = 1.9, CI = 1.0-3.7) and aggression (OR = 1.6, CI = 0.9-2.7), and low levels of careful/cautious behavior (OR = 1.8, CI = 1.1-2.9). Children with low levels of self-regulation had reduced risks (OR = 0.4, CI = 0.2-0.8).Discussion
Results suggest that children's behaviors affect their risk of agricultural injury. Additional research could elucidate mechanisms and inform interventions.Impact on industry
The development of multifaceted, sustainable approaches for prevention is necessary for this unique population. These findings suggest a need for interventions that incorporate specific behavior-related risk factors in the context of family farms and ranches. 相似文献39.
F. R. Funes-Monzote Marta Monzote E. A. Lantinga H. van Keulen 《Environment, Development and Sustainability》2009,11(4):765-783
From the 1960s onwards, a ‘High External Input’ dairy production model was applied widely in Cuba. Overall milk production
of the national herd increased considerably, but the system was inefficient from both a financial and energetic point of view.
In the early 1990s, after the abrupt end of inflow of capital and other resources from Eastern Europe, the dairy sector collapsed.
In the short term, the modern infrastructure of milk production deteriorated and the sector experienced profound vulnerability.
However, in the longer term, this situation stimulated a search for more sustainable approaches, such as low external input
Mixed Farming Systems (MFS). The current study aimed to evaluate two small scale prototype farms to assess the implications
of converting ‘Low External Input’ Dairy Farming Systems into MFS. Fifteen agro-ecological and financial indicators were selected
and monitored over a 6-year period. Two configurations of MFS, i.e. the proportion of the farm area occupied by arable crops,
were tested: 25 and 50%. Productivity, energy efficiency and cost-effectiveness all improved following conversion. Total energy
input was low for both farms and decreased over time, whereas energy efficiency was high and increased over time. Human labour
input was high directly following conversion, but decreased by one-third over the 6-year period. This study demonstrates,
at an experimental scale, the potential of MFS to achieve ecological, productivity and financial advantages for dairy production
in Cuba.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
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Geoffrey R. Squire Cathy Hawes Graham S. Begg Mark W. Young 《Environmental science and pollution research international》2009,16(1):85-94