Abstract
Across the globe, human activities have been gaining importance relatively to climate and ecology as the main controls on fire regimes and consequently human activity became an important driver of the frequency, extent and intensity of vegetation burning worldwide. Our objective in the present study is to look for weekly cycles in vegetation fire activity at global scale as evidence of human agency, relying on the original MODIS active fire detections at 1 km spatial resolution (MCD14ML) and using novel statistical methodologies to detect significant periodicities in time series data. We tested the hypotheses that global fire activity displays weekly cycles and that the weekday with the fewest fires is Sunday. We also assessed the effect of land use and land cover on weekly fire cycle significance by testing those hypotheses separately for the Villages, Settlements, Croplands, Rangelands, Seminatural, and Wildlands anthromes. Based on a preliminary data analysis of the daily global active fire counts periodogram, we developed an harmonic regression model for the mean function of daily fire activity and assumed a linear model for the de-seasonalized time series. For inference purposes, we used a Bayesian methodology and constructed a simultaneous 95% credible band for the mean function. The hypothesis of a Sunday weekly minimum was directly investigated by computing the probabilities that the mean functions of every weekday (Monday to Saturday) are inside the credible band corresponding to mean Sunday fire activity. Since these probabilities are small, there is statistical evidence of significantly fewer fires on Sunday than on the other days of the week. Cropland, rangeland, and seminatural anthromes, which cover 70% of the global land area and account for 94% of the active fires analysed, display weekly cycles in fire activity. Due to lower land management intensity and less strict control over fire size and duration, weekly cycles in Rangelands and Seminatural anthromes, which jointly account for 53.46% of all fires, although statistically significant are weaker than those detected in Croplands.
Highlights
Across the globe, human activities have been gaining importance relatively to climate and ecology as the main controls on fire regimes, and during the last few decades anthropogenic vegetation burning expanded its impact on land cover, ecosystem dynamics, and atmospheric greenhouse gas emissions from regional to global scales[1,2,3,4]
23 found significantly weekly cycles in sub-Saharan Africa cropland burning, with Sunday minima in predominantly Christian regions and Friday minima in mainly Muslim regions
AQUA was launched in mid-2002 with a 2:30AM/ PM overpass and that more than doubled the amount of active fires detected because the AQUA daytime overpass observes the most active period of the diurnal cycle of vegetation burning
Summary
Human activities have been gaining importance relatively to climate and ecology as the main controls on fire regimes, and during the last few decades anthropogenic vegetation burning expanded its impact on land cover, ecosystem dynamics, and atmospheric greenhouse gas emissions from regional to global scales[1,2,3,4]. [23] found significantly weekly cycles in sub-Saharan Africa cropland burning, with Sunday minima in predominantly Christian regions and Friday minima in mainly Muslim regions They did not find significant weekly cycles in fire activity in densely settled areas, where vegetation burning is very limited, nor in rangelands, forests and wildlands, where fire management intensity is weaker than in croplands. These continental-scale findings, combined with the recognition of the strongly anthropogenic nature of global vegetation burning[24] motivated the hypothesis of weekly cycles in global fire activity, as observed with remotely sensed active fire data. These differences are likely to affect the results of a weekly cycle analysis
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