Encontrados 10 documentos, a visualizar página 1 de 1
Wildfire selectivity for land cover type: does size matter ?
Barros, Ana M.G.; Pereira, J.M.C.Previous research has shown that fires burn certain land cover types disproportionally to their abundance. We used quantile regression to study land cover proneness to fire as a function of fire size, under the hypothesis that they are inversely related, for all land cover types. Using five years of fire perimeters, we estimated conditional quantile functions for lower (avoidance) and upper (preference) quantil...
A test for directional-linear independence, with applications to wildfire orien...
GarcÃa-Portugués, Eduardo; Barros, Ana M.G.; Crujeiras, Rosa M.; González-Manteiga, Wenceslao; Pereira, J.M.C.Original Paper ; A nonparametric test for assessing the independence between a directional random variable (circular or spherical, as particular cases) and a linear one is proposed in this paper. The statistic is based on the squared distance between nonparametric kernel density estimates and its calibration is done by a permutation approach. The size and power characteristics of various variants of the test a...
Spatial characterization of wildfire orientation patterns in California
Barros, Ana M.G.; Pereira, J.M.C.; Moritz, Max A.; Stephens, Scott L.Using 100 years of fire perimeter maps, we investigate the existence of geographical patterns in fire orientation across California. We computed fire perimeter orientation, at the watershed level, using principal component analysis. Circular statistics were used to test for the existence of preferential fire perimeter orientations. Where perimeters displayed preferential orientation, we searched for evidence of...
Fire frequency analysis in Portugal (1975-2005), using Landsat-based burnt area...
Oliveira, Sofia L.J.; Pereira, J.M.C.; Carreiras, João M.B.Fire frequency in 21 forest planning regions of Portugal during the period 1975–2005 was estimated from historical burnt area maps generated with semi-automatic classification of Landsat Thematic Mapper (TM) satellite imagery. Fire return interval distributions were modelled with the Weibull function and the estimated parameters were used to calculate regional mean, median and modal fire return intervals, as ...
Identifying geographical patterns of wildfire orientation: a watershed-based an...
Barros, Ana M.G.; Pereira, J.M.C.; Lund, Ulric J.We searched for geographical patterns in the orientation of wildfires, using watersheds as spatial support for the analysis. An 1975–2005 annual fire atlas of mainland Portugal was used to compute the orientation of fire perimeters and watersheds, using principal component analysis. Circular statistics were employed to test for the existence of a preferred, as opposed to random, mean fire orientation in each ...
Spatial extremes of wildfire sizes: Bayesian hieralquical models for extremes
Mendes, Jorge M.; Bermudez, Patricia Cortés de Zea; Pereira, J.M.C.; Turkman, K.F.; Vasconcelos, M.J.P.In Portugal, due to the combination of climatological and ecological factors, large wildfires are a constant threat and due to their economic impact, a big policy issue. In order to organize efficient fire fighting capacity and resource management, correct quantification of the risk of large wildfires are needed. In this paper, we quantify the regional risk of large wildfire sizes, by fitting a Generalized Pare...
Global fire activity patterns (1996-2006) and climatic influence: an analysis u...
Le Page, Y.; Pereira, J.M.C.; Trigo, R.; Camara, C.; Oom, D.; Mota, B.Vegetation fires have been acknowledged as an environmental process of global scale, which affects the chemical composition of the troposphere, and has profound ecological and climatic impacts. However, considerable uncertainty remains, especially concerning intra and inter-annual variability of fire incidence. The main goals of our globalscale study were to characterise spatial-temporal patterns of fire activi...
The North Atlantic oscillation and European vegetation dynamics
Gouveia, Célia; Trigo, Ricardo M.; Camara, Carlos C.; Libonati, Renata; Pereira, J.M.C.The relationship between vegetation greenness and the North Atlantic Oscillation (NAO) is assessed over Europe. The study covers the 21-year period from 1982 to 2002 and is based on monthly composites of the Normalised Difference Vegetation Index (NDVI) and Brightness Temperature from the Global Inventory Monitoring and Modelling System (GIMMS) as well as on monthly precipitation from the Global Precipitation C...
Global wildland fire emissions from 1960 to 2000
Schultz, Martin G.; Heil, Angelika; Hoelzemann, Judith J.; Spessa, Allan; Thonicke, Kirsten; Goldammer, Johann; Held, Alexander C.; Pereira, J.M.C.In many regions of the world, fires are an important and highly variable source of air pollutant emissions, and they thus constitute a significant if not dominant factor controlling the interannual variability of the atmospheric composition. This paper describes the 41-year inventory of vegetation fire emissions constructed for the Reanalysis of the Tropospheric chemical composition over the past 40 years proje...
Leaf area estimation from tree allometrics in Eucalyptus globulus plantations
Fabião, António; Pereira, J.M.C.; Tomé, Margarida; Carreiras, J.M.B.; Tomé, José; Pereira, J.S.; David, J.S.Data from five studies on the relationships between dendrometric measurements and leaf area of Eucalyptus globulus Labill. plantations were pooled and analyzed to develop regression models for the estimation of leaf area of individual trees. The data, collected at two sites in west-central and southwestern Portugal, varied in age from 2 to 19 years and in plant density from 481 to 1560 trees/ha and included bot...
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