Biomass burning spatiotemporal variations over South and Southeast Asia

Abstract:

In this study, MODIS active fire and land use products were integrated to classify and evaluate biomass burning (BB) spatiotemporal variations over South Asia (SA) and Southeast Asia (SEA). Meanwhile, two indicators of BB intensity are considered, the number of fire spots and fire radiative power (FRP). Because the BB time series in equatorial SEA was too noisy, a more robust trend analysis, Siegel’s repeated median estimator (RME), was adopted to reduce the influence of outliers. Additionally, a monotonic trend analysis and two geographic distribution analyses were conducted to further quantify the interannual variations and summarize the spatial characteristics of BB. Analyses were conducted at several scales, including at a 0.25˚×0.25˚ grid-scale. The results indicated that BB in SA was dominated by crop residue burning (CRB). From 2001 to 2018, CRB in SA significantly increased by 844 spots/yr. The increase region was primarily distributed in central/southern India and eastern Pakistan. CRB in Punjab-Haryana, which was deemed as a significant source of air pollution for the Indo-Gangetic Plain, presented a substantial declining trend. BB in mainland SEA was more intense than that in the other regions, and the principal forms are forest and shrubland fires. Forest fires in mainland SEA declined at a rate of -209 spots/yr, and shrubland fires grew at a rate of 803 spots/yr, which was likely related to the dramatic land cover changes induced by local swidden agriculture. Unlike the other regions, BB in equatorial SEA primarily occurred in the second half of the year, and shrubland fires constituted over 50% of the local BB. BB in equatorial SEA was extremely vulnerable to El Niño events, and when the annual SST anomalies within the Niño 3 region improved by 1 ℃, the annual number of BB spots and FRP of equatorial SEA increased by 51,800 and 2.40×10⁶ MW, respectively. Although the interannual variation in equatorial SEA is dramatic, the RME still reveals that the BB significantly declined by -1,825 spots/yr and that as the principal form of BB, shrubland fires declined by -1,083 spots/yr.