Understanding spatial and temporal patterns of burned areas at regional scales, provides a long-term perspective of fire processes and its effects on ecosystems and vegetation recovery patterns, and it is a key factor to design prevention and post-fire restoration plans and strategies. Remote sensing has become the most widely used tool to detect fire affected areas over large tracts of land (e.g., ecosystem, regional and global levels). Standard satellite burned area and active fire products derived from the 500-m Moderate Resolution Imaging Spectroradiometer (MODIS) and the Satellite Pour l’Observation de la Terre (SPOT) are available to this end. However, prior research caution on the use of these global-scale products for regional and sub-regional applications. Consequently, we propose a novel semi-automated algorithm for identification and mapping of burned areas at regional scale. The semi-arid Monte shrublands, a biome covering 240,000 km2 in the western part of Argentina, and exposed to seasonal bushfires was selected as the test area. The algorithm uses a set of the normalized burned ratio index products derived from MODIS time series; using a two-phased cycle, it firstly detects potentially burned pixels while keeping a low commission error (false detection of burned areas), and subsequently labels them as seed patches. Region growing image segmentation algorithms are applied to the seed patches in the second-phase, to define the perimeter of fire affected areas while decreasing omission errors (missing real burned areas). Independently-derived Landsat ETM+ burned-area reference data was used for validation purposes. Additionally, the performance of the adaptive algorithm was assessed against standard global fire products derived from MODIS Aqua and Terra satellites, total burned area (MCD45A1), the active fire algorithm (MOD14); and the L3JRC SPOT VEGETATION 1 km GLOBCARBON products. The correlation between the size of burned areas detected by the global fire products and independently-derived Landsat reference data ranged from R2 = 0.01–0.28, while our algorithm performed showed a stronger correlation coefficient (R2 = 0.96). Our findings confirm prior research calling for caution when using the global fire products locally or regionally. 相似文献
Forest fires are one of the most important causes of environmental alteration in Mediterranean countries. Discrimination of different degrees of burn severity is critical for improving management of fire-affected areas. This paper aims to evaluate the usefulness of land surface temperature (LST) as potential indicator of burn severity. We used a large convention-dominated wildfire, which occurred on 19–21 September, 2012 in Northwestern Spain. From this area, a 1-year series of six LST images were generated from Landsat 7 Enhanced Thematic Mapper (ETM+) data using a single channel algorithm. Further, the Composite Burn Index (CBI) was measured in 111 field plots to identify the burn severity level (low, moderate, and high). Evaluation of the potential relationship between post-fire LST and ground measured CBI was performed by both correlation analysis and regression models. Correlation coefficients were higher in the immediate post-fire LST images, but decreased during the fall of 2012 and increased again with a second maximum value in summer, 2013. A linear regression model between post-fire LST and CBI allowed us to represent spatially predicted CBI (R-squaredadj > 85%). After performing an analysis of variance (ANOVA) between post-fire LST and CBI, a Fisher's least significant difference test determined that two burn severity levels (low-moderate and high) could be statistically distinguished. The identification of such burn severity levels is sufficient and useful to forest managers. We conclude that summer post-fire LST from moderate resolution satellite data may be considered as a valuable indicator of burn severity for large fires in Mediterranean forest ecosytems. 相似文献
The potential of the short-wave infrared (SWIR) bands to detect dry-season vegetation mass and cover fraction is investigated with ground radiometry and MODIS data, confronted to vegetation data collected in rangeland and cropland sites in the Sahel (Senegal, Niger, Mali). The ratio of the 1.6 and 2.1 μm bands (called STI) acquired with a ground radiometer proved well suited for grassland mass estimation up to 2500 kg/ha with a linear relation (r2 = 0.89). A curvilinear regression is accurate for masses ranging up to 3500 kg/ha. STI proved also well suited to retrieve vegetation cover fraction in crop fields, fallows and rangelands. Such dry-season monitoring, with either ground or satellite data, has important applications for forage, erosion risk and fire risk assessment in semi-arid areas. 相似文献
On the basis of improving the algorithm of the mixing length in and above forest canopies, a PBL numerical model including the multi-layer, heterogeneous vegetation is developed. Simulations indicate that different treatments of mixing length can make a great difference in the wind field especially for dense forest, and results from the improved mixing length scheme are in better agreement with observations than those from the original scheme. It may be expected that the improved mixing length scheme can lead to more ra-tional turbulent transfer than the original one. From the sensitivity experiments, we obtain the characteris-tics of both wind and temperature profiles in and above plant canopies, e.g., during the daytime, a stable thermal stratification exists near the surface in the canopies, but a neutral or slightly unstable condition ap-pears above plant canopies, while at night the reverse situations occur; the increase of the temperature of the dense-forest case is less than that of the sparse-forest case; the windspeed is reduced within the canopy lay-er and the large wind shear occurs near the treetop, etc. 相似文献
Desalinization effects on benthic diatom communities were investigated in two adjacent streams in Northern Thuringia, the creek Urbach and the river Helbe. Salt-saturated stockpile effluents had been introduced into the Urbach until 1996, resulting in fluctuating chloride concentrations with maximum values up to 25.4 g · 1−1 (Helbe: max. 3.7 g · 1−1).
The diatom vegetation and hydrographical and chemical data of an Urbach site were compared to those of a sampling site further downstream. Monthly sampling in 1996 started at the end of salt influx in January. Reference samples from the years 1995, 1986 and 1963 were evaluated along with the 1996 samples.
After termination of the introduction of salt-loaded effluents, relative abundances of brackish water species greatly decreased within three months. The Halobion Index (Ziemann 1982), reflecting osmotic and ion composition effects on diatoms, decreased until May 1996, then stabilized. In summer 1996, several diatoms had a mass development, showing that salinization impacts had previously overruled effects of other environmental variables. 相似文献
The flow division at an open channel junction is affected by the inflow discharge and the downstream water depths of the junction. The growth of vegetation in a channel system is environmental friendly, but its effect on the flow in an open channel junction can be significant. In this work a 3D RANS (Reynolds Averaged Navier–Stokes equation) model has been implemented to investigate the flow phenomena in channel junctions with or without vegetation. The model is first validated by two cases: flow in an open channel T-junction without vegetation, and flow in a single open channel with vegetation. The model is then applied to simulate flow in an open channel T-junction with varying width ratio and vegetation density of the branch channel. The results quantitatively predict the trend of increasing flow in the branch channel with the increase in branch channel width and/or the decrease in vegetation density. The overall energy loss coefficient of the system, however, decreases with the amount of flow in the branch channel. 相似文献
Surface crusts and seals can form from a variety of processes, both physical and biological, and have the potential to alter runoff and erosion, especially in regions with low vegetation covers. Despite the obvious links between seals and crusts these features have rarely been considered together. This study uses rainfall simulation experiments to investigate interrill soil crust and seal development in response to structural (or raindrop-impact-induced) and depositional (or runoff-induced) processes on a semiarid piedmont in southern New Mexico, USA, which has undergone substantive vegetation change (replacement of grasses by shrubs) over the last 100 years. The study design incorporates six double-paired runoff plots divided into four subplots, each of which was exposed to three rainfall simulation events. Crust development on these plots was assessed using penetration-resistance measurements while seal development was assessed using runoff coefficients. The penetration-resistance data indicate that subplots directly exposed to raindrop impacts (uncovered plots) have crusts that are 40% stronger than those positioned beneath a mesh cover (covered plots) that intercepts the kinetic energy of the rainfall. The crusts exposed to raindrop-impacts increased in strength following each simulation, whereas the crusts on the covered surfaces reached a plateau after two events.Runoff data indicate that seal development does not directly mirror crust formation. Runoff coefficients increased after each rainfall simulation event but were not significantly different between the covered and uncovered plots. Rather, the presence of stone lags or litter on the soil surface influenced the relation between runoff and seal development. Sediment yields from uncovered surfaces exceeded those from covered surfaces, indicating that raindrop impacts contribute to the delivery of sediment into flows. The results of this study indicate that the loss of vegetation cover on the piedmont has increased the extent of surface crust and seal development but that those crusts may be playing an important role in mitigating erosion. 相似文献
Burned area mapping is an essential step in the forest fire research to investigate the relationship between forest fire and climate change and the effect of forest fire on carbon budgets. This study proposed an algorithm to map forest fire burned area using the Moderate-Resolution Imaging Spectroradiameter (MODIS) time series data in Heilongjiang Province, China. The algorithm is divided into two steps: Firstly, the ‘core’ pixels were extracted to represent the most possible burned pixels based on the comparison of the temporal change of Global Environmental Monitoring Index (GEMI), Burned Area Index (BAI) and MODIS active fire products between pre- and post-fires. Secondly, a 15-km distance was set to extract the entire burned areas near the ‘core’ pixels as more relaxed conditions were used to identify the fire pixels for reducing the omission error as much as possible. The algorithm comprehensively considered the thermal characteristics and the spectral change between pre- and post-fires, which are represented by the MODIS fire products and the spectral index, respectively. Tahe, Mohe and Huma counties of Heilongjiang Province, China were chosen as the study area for burned area mapping and a time series of burned maps were produced from 2000 to 2011. The results show that the algorithm can extract burned areas more accurately with the highest accuracy of 96.61%. 相似文献