Obtaining quantitative information about the recovery of fire-affected ecosystems is of utmost importance from the management and decision-making point of view. Nowadays the concern about natural environment protection and recovery is much greater than in the past. However, the resources and tools available for its management are still not sufficient. Thus, attention and precision is needed when decisions must be taken. Quantitative estimates on how the vegetation is recovering after a fire can be of help for evaluating the necessity of human intervention on the fire-affected ecosystem, and their importance will grow as the problem of forest fires, climate change and desertification increases.This article performs a comparison of methods to extract quantitative estimates of vegetation cover regrowth with Landsat TM and ETM+ data in an area that burned during the summer of 1998 in the Liguria region (Italy). In order to eliminate possible sources of error, a thorough pre-processing was carried out, including a careful geometric correction (reaching RMSE lower than 0.3 pixels), a topographic correction by means of a constrained Minnaert model and a combination of absolute and relative atmospheric correction methods. Pseudo Invariant Features (PIF) were identified by implementing an automated selection method based in temporal Principal Component Analysis (PCA), which has been called multi-Temporal n-Dimensional Principal Component Analysis (mT-nD-PCA).Spectral Mixture Analysis (SMA) was compared against quantitative vegetation indices which are based on well known traditional vegetation indices like Normalized Difference Vegetation Index (NDVI) and Modified Soil Adjusted Vegetation Index (MSAVI). Accuracy assessment was performed by regressing vegetation cover results obtained with each method against field data gathered during the fieldwork campaign carried out in the study area. Results obtained showed how vegetation cover fractions extracted from the NDVI based quantitative index were the most accurate, being superior to the rest of the techniques applied, including SMA. 相似文献
A mathematical model is presented which allows one to treat the combined phenomena of heat, mass and species transfer by diffusion as they occur within smouldering fires in accumulations of dust or other solid bulk materials. The model was applied to predict self-ignition temperatures of five different dusts, where it could be shown that computed and experimental self-ignition temperatures coincide within an error margin of ±5%.
For smouldering fires, if initiated by either self-ignition or an ignition source, it could be shown that the temperature and the velocity at which the reaction front propagates both depend on the volume of the dust accumulation. In addition, the propagation velocity increases when the initial temperature of the dust accumulation is increased and decreases when the initial moisture content of the dust accumulation is increased.
Comparisons of the numerical model with experiments show that the smouldering propagation is mirrored qualitatively, while the accuracy of the computations strongly depends on the accuracy of the input parameters, namely on the apparent activation energy. 相似文献
Climate change incurs costs, but government adaptation budgets are limited. Beyond a certain point, individuals must bear
the costs or adapt to new circumstances, creating political-economic tipping points that we explore in three examples. First,
many Alaska Native villages are threatened by erosion, but relocation is expensive. To date, critically threatened villages
have not yet been relocated, suggesting that we may already have reached a political-economic tipping point. Second, forest
fires shape landscape and ecological characteristics in interior Alaska. Climate-driven changes in fire regime require increased
fire-fighting resources to maintain current patterns of vegetation and land use, but these resources appear to be less and
less available, indicating an approaching tipping point. Third, rapid sea level rise, for example from accelerated melting
of the Greenland ice sheet, will create a choice between protection and abandonment for coastal regions throughout the world,
a potential global tipping point comparable to those now faced by Arctic communities. The examples illustrate the basic idea
that if costs of response increase more quickly than available resources, then society has fewer and fewer options as time
passes. 相似文献
The grid-net system estimating the electrical conductivity changes was evaluated as a potential detection system for the leakage of diesel fuel and landfill leachate. Aspects of electrical conductivity changes were varied upon the type of contaminant. The electrical conductivity in the homogeneous mixtures of soil and landfill leachate linearly increased with the ionic concentration of pore fluid, which became more significant at higher volumetric water contents. However, the electrical conductivity in soil/diesel fuel mixture decreased with diesel fuel content and it was more significant at lower water contents. The electrode spacing should be determined by considering the type of contaminant to enhance the electrode sensitivity especially when two-electrode sensors are to be used. The electrode sensitivity for landfill leachate was constantly maintained regardless of the electrode spacings while that for the diesel fuel significantly increased at smaller electrode spacings. This is possibly due to the fact that the insulating barrier effect of the diesel fuel in non-aqueous phase was less predominant at large electrode spacing because electrical current can form the round-about paths over the volume with relatively small diesel fuel content. The model test results showed that the grid-net detection system can be used to monitor the leakage from waste landfill and underground storage tank sites. However, for a successful application of the detection system in the field, data under various field conditions should be accumulated. 相似文献
The long-term behavior of 90Sr was investigated from 1987 to 1997 in fifteen lakes in southern and central Finland following the 1986 Chernobyl accident. Both water and fish samples (perch, pike, vendace) were analyzed. 90Sr stays long in the freshwater ecosystem; the observed half-lives during the study period were generally around 10 years in water and even longer in fish. One lake exhibited very different behavior for 90Sr, with elevated levels in fish and water and very short observed half-life in fish, less than 2 years. Concentration factors of 90Sr in fish (Bqkg−1 f.w. in fish/Bqkg−1 in water) among the studied lakes significantly correlated with both the Ca concentration and electrical conductivity of the water. More 90Sr was transferred into fish in lakes with a low electrical conductivity and a low Ca concentration. Among other water parameters evaluated were pH, color, total nitrogen, and phosphorus. 相似文献