Research Article

A human-driven decline in global burned area

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Science  30 Jun 2017:
Vol. 356, Issue 6345, pp. 1356-1362
DOI: 10.1126/science.aal4108
  • Fig. 1 Satellite observations show a declining trend in fire activity across the world’s tropical and temperate grassland ecosystems and land-use frontiers in the Americas and Southeast Asia.

    (A) mean annual burned area and (B) trends in burned area (GFED4s, 1998 through 2015). Line plots (inset) indicate global burned area and trend distributions by fractional tree cover (28).

  • Fig. 2 A decrease in the number of fires was the primary driver of the global decline in burned area.

    Normalized variation (2003 = 1) and linear trends in (A) burned area, (B) number of fires, and (C) mean fire size derived from the MODIS 500m product (MCD64A1). Shading denotes 95% prediction intervals. Adjusting for precipitation-driven trends in burned area isolated residual trends associated with other factors, including human activity (28). (D) Summary of trends in global burned area, calculated as the product of the number and size of fires, after adjusting for the influence of precipitation. Regional trends in fire number and fire size are provided in Table 1, table S1, and fig. S7.

  • Fig. 3 Comparison of burned area trends from satellite observations (GFED4s) and prognostic fire models from FireMIP.

    (A) Time series of global burned area. (B) A comparison of global mean annual burned area versus the relative trend in global mean burned area from the observations and models. GFED4s observations are shown in black and FireMIP models are shown with different colors. FireMIP model estimates were available from 1997 through 2013 for six models, from 1997 through 2012 for the CTEM fire module and JULES-INFERNO, and from 1997 through 2009 for MC-Fire. The FireMIP models are described in more detail in the supplementary materials and by Rabin et al. (34) (tables S3 and S4 and fig. S8).

  • Fig. 4 Population and agriculture influence the spatial pattern of burned area, with contrasting impacts in different biomes.

    Maps of the spatial correlation between burned area and (A) population density per km2, (B) fractional cropland area, and (C) livestock density per km2. Map panels indicate the spatial correlation between burned area (GFED4s) and human land use for the 36 0.25° pixels within each 1.5° grid cell. Line plots (inset) show the mean correlation as a function of fractional tree cover (28).

  • Fig. 5 Conceptual model showing changes in fire use along the continuum from common land ownership to highly capitalized agricultural management on private lands.

    In humid tropical regions (A and B) (precipitation ≥1200 mm year−1), deforestation fires for agricultural expansion (A) lead to peak burned area during an early land-use transition phase to more settled land uses (B). In the semi-arid tropics (C and D) (precipitation 500 to 1200 mm year−1), burned area is highest under common land ownership (D), as intact savanna and grazing lands allow for the spread of large fires. Conversion of savanna and grassland systems for more permanent agriculture (C) drives a nonlinear decline in burned area from landscape fragmentation and changing fire use for agricultural management (D). The conceptual model is based on the spatial distribution of burned area, land use, population, and GDP (28) (figs. S12 and S13). Similar patterns are observed across all continents, but absolute burned area differs as a function of culture, climate, and vegetation.

  • Table 1 Relative trends in burned area, number of fires, and mean fire size for different regions of the world.

    Trends are shown for different time periods, as indicated, to directly compare burned area estimates from different sources. All trends were calculated by using fire season estimates of burned area, with the exception of the FireMIP data, which were produced per calendar year (28). Increases (regular type) and decreases (bold) in burned area are indicated for each region and time period; significant trends are denoted by asterisks (*P < 0.1, **P < 0.05, and ***P < 0.01).

    Fire productTime
    period
    Full or
    residual*
    Trend (% year−1) with 95% confidence limits
    WorldNorth
    America
    South
    America
    EurasiaSoutheast
    Asia
    AfricaAustralia
    Burned area
    (GFED4s)
    1998–2015Full–1.35 (0.49)***–0.37 (2.66)–1.68 (2.75)–0.80 (1.98)0.23 (1.94)–1.27 (0.32)***–2.53 (4.23)
    PA–0.99 (0.29)***0.40 (2.13)–0.51 (1.68)–0.26 (1.34)0.25 (1.32)–1.26 (0.25)***–0.67 (1.91)
    Burned area
    (GFED4s)
    during the
    MODIS era
    2003–2015Full–1.27 (0.95)**–0.08 (2.17)–2.66 (5.38)–2.18 (2.98)–0.30 (3.23)–1.51 (0.51)***1.48 (7.95)
    PA–1.17 (0.39)***0.33 (1.77)–1.75 (3.14)–1.24 (1.96)–0.13 (2.02)–1.45 (0.42)***0.39 (3.16)
    Burned area from
    500m MODIS
    MCD64A1
    2003–2015Full–1.15 (1.21)*0.61 (2.76)–1.40 (6.99)–2.23 (4.13)–0.62 (3.92)–1.60 (0.56)***1.53 (8.21)
    PA–1.23 (0.44)***0.78 (2.12)–1.09 (3.64)–1.02 (2.35)–0.61 (2.46)–1.68 (0.46)***0.56 (3.40)
    Fire number2003–2015Full–0.98 (0.73)**–1.44 (2.92)–2.67 (4.98)–3.56 (4.39)–1.10 (3.36)–0.87 (0.38)***1.50 (6.59)
    PA–1.00 (0.35)***–1.41 (2.37)–2.13 (2.55)*–3.46 (3.06)**–1.03 (1.96)–0.88 (0.30)***0.73 (2.83)
    Fire size2003–2015Full–0.39 (0.38)**0.47 (1.73)1.39 (2.32)–0.09 (2.03)–0.68 (0.99)–0.78 (0.29)***–0.29 (1.69)
    PA–0.43 (0.18)***0.32 (1.28)1.29 (1.28)**–0.16 (1.36)–0.69 (0.85)–0.81 (0.21)***0.08 (1.11)
    Burned area
    predicted
    by FireMIP
    1997–2013Full–0.13 (0.56)–0.36 (1.37)–0.06 (0.77)0.06 (0.53)–1.89 (1.95)–0.25 (0.70)–0.50 (2.42)

    *Residual time series, after adjusting for the influence of precipitation variability (PA), were estimated by using the approach described in the supplementary materials.

    †Eurasia excludes regions in Southeast Asia.

    ‡In this instance, numbers in parentheses are the standard deviation of the trend averaged across the different FireMIP models (n = 9).

    Supplementary Materials

    • A human-driven decline in global burned area

      N. Andela, D. C. Morton, L. Giglio, Y. Chen, G. R. van der Werf, P. S. Kasibhatla, R. S. DeFries, G. J. Collatz, S. Hantson, S. Kloster, D. Bachelet, M. Forrest, G. Lasslop, F. Li, S. Mangeon, J. R. Melton, C. Yue, J. T. Randerson

      Materials/Methods, Supplementary Text, Tables, Figures, and/or References

      Download Supplement

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