The spatio-temporal characteristics of forest fires in China: observations from hybrid remote sensing data

Forest fire is a natural disaster threatening global human well-beings as well as a crucial disturbance agent driving forest landscape changes. The remotely sensed burned area (BA) products can provide spatially and temporally continuous monitoring of global fires, but the accuracies remain to be improved. We firstly developed a hybrid burned area mapping approach, which integrated the advantages of a 250 m global BA product (CCI_Fire) and a 30 m global forest change (GFC) product, to generate an improved 250 m BA product (so-called CCI_GFC product). Based on 248 fire patches derived from Landsat imagery, the results showed that the CCI_GFC product improved the CCI_Fire product substantially, which are significantly better than MCD64A1 product. According to the CCI_GFC, we found the total BA in the past 17 years was about 12.1 million ha in China, which approximately covered 6.1% of the total forested areas with a significantly decreased trend through Mann-Kendall test (Tau= -0.47, P<0.05) . We conducted a grid analysis (0.05°×0.05°) to determine the hot spots of forest fire from 2001 to 2017. We also quantified fire characteristics on frequency, spatial distribution, and seasonality in terms of Burned Forest Rate (BFR), hot spot areas, and fire seasons, respectively. We found that low frequency burns with a 0<BFR≤20% in 17 years covered 64% of total grids; the medium-low frequency burns (20%<BFR≤40%), the medium frequency burns (40%<BFR≤60%), the medium-high frequency burns (60%< BFR≤80%) accounted for 15%, 7%, 4% respectively; the high frequency burns (80%<BFR≤100%) and extremely high burns (100%<BFR≤120%) together occupy 10% of total grids which mainly distributed in Xiao Hinggan mountains, south China, and southwest China. The seasonality of forest fires differed substantially among eco-regions. The fire seasons of two temperate forest eco-regions are spring and autumn. The two peak fire months are May and October, in which about 22% and 37% of the total burned area were founded respectively. As a comparison, fire seasons in tropical and subtropical eco-regions are spring and winter (i.e., November to March of the next year), which accounted 88% of the total burned area. Our study clearly illustrated the characteristics of forest fire patterns in the past 17 years, which highlighted the remarkable achievements due to a nationwide implementation of fire prevention policy. At the same time, we emphasized that it is critically important to regard the long-term forest fire dynamics to design scientific and reasonable strategies or methods for fire management and controlling, which will be of sound significance to optimize the allocation of financial resources on fire management, and to achieve sustainable management of forests.