Editing IPCC:AR6/WGII/Chapter-2 (section)

===== 2.4.4.2.3 Observed changes in wildfire in individual regions with complex attribution =====

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While burned area has increased in parts of Asia, Australia, Europe and South America, published research has not yet attributed the increases to anthropogenic climate change ( ''medium evidence'' , ''high agreement'' ).

In the Amazon, deforestation for agricultural expansion and the degradation of forests adjacent to deforested areas cause wildfire in moist humid tropical forests not adapted to fire ( ''robust evidence'' , ''high agreement'' ) ( [[#Fonseca--2017|Fonseca et al., 2017]] ; [[#van%20Marle--2017|van Marle et al., 2017]] ; [[#da%20Silva--2018|da]] [[#Silva--2018|Silva et al., 2018]] ; [[#da%20Silva--2021|da Silva et al., 2021]] ; [[#dos%20Reis--2021|dos Reis et al., 2021]] ; [[#Libonati--2021|Libonati et al., 2021]] ). Roads facilitate deforestation, fragmenting the rainforest and increasing the dryness and flammability of vegetation ( [[#Alencar--2015|Alencar et al., 2015]] ). Extreme droughts that occur during warm phases of the ENSO and the Atlantic Multi-Decadal Oscillation combine with the degradation of vegetation to cause extreme fire events ( ''robust evidence'' , ''high agreement'' ) ( [[#Fonseca--2017|Fonseca et al., 2017]] ; [[#Aragao--2018|Aragao et al., 2018]] ; [[#da%20Silva--2018|da]] [[#Silva--2018|Silva et al., 2018]] ; [[#Burton--2020|Burton et al., 2020]] ; [[#dos%20Reis--2021|dos Reis et al., 2021]] ; [[#Libonati--2021|Libonati et al., 2021]] ). In the State of Roraima, Brazil, distance to roads and infrastructure that enable deforestation and ENSO were the factors most explaining fire occurrence in the extreme 2015–2016 fire season ( [[#Fonseca--2017|Fonseca et al., 2017]] ). From 1973 to 2014, burned area increased in the Amazon, coinciding with increased deforestation ( [[#van%20Marle--2017|van Marle et al., 2017]] ). In the State of Acre, Brazil, burned area increased 36-fold from 1984 to 2016, with 43% burned in agricultural and livestock settlement areas ( [[#da%20Silva--2018|da]] [[#Silva--2018|Silva et al., 2018]] ). In the extreme fire year 2019, 85% of the area burned in the Amazon occurred in areas deforested in 2018 ( [[#Cardil--2020|Cardil et al., 2020]] ). Even though relatively higher moisture in 2019 led to burning below the 2002–2019 average across most of South America, burning in areas of recent deforestation in the Amazon were above the 2002–2019 average, indicating that deforestation, not meteorological conditions, triggered the 2019 fires ( [[#Kelley--2021|Kelley et al., 2021]] ; [[#Libonati--2021|Libonati et al., 2021]] ). Furthermore, from 1981 to 2018, deforestation in the Amazon reduced moisture inputs to the lower atmosphere, increasing drought and fire in a self-reinforcing feedback ( [[#Xu--2020|Xu et al., 2020]] ). In the Amazon, deforestation exerts an influence on wildfire that can be stronger than climate change ( ''robust evidence'' , ''high agreement'' ).

In Australia, burned area increased significantly between the periods 1950–2002 and 2003–2020 in the southeast state of Victoria, with the area burned in the 2019–2020 bushfires being the highest on record ( [[#Lindenmayer--2020|Lindenmayer and Taylor, 2020]] ). In addition to the deaths of dozens of people and the destruction of thousands of houses, the 2019–2020 bushfires burned almost half of the area protected for conservation in Victoria, two-thirds of the forests allocated for timber harvesting ( [[#Lindenmayer--2020|Lindenmayer and Taylor, 2020]] ), wildlife and extensive areas of habitat for threatened plant and animal species ( [[#Geary--2021|Geary et al., 2021]] ). Generally, past timber harvesting did not lead to more severe fire canopy damage ( [[#Bowman--2021b|Bowman et al., 2021b]] ). Across southeastern Australia, the fraction of vegetated area that burned increased significantly in eight of the 32 bioregions from 1975 to 2009, but decreased significantly in three bioregions ( [[#Bradstock--2014|Bradstock et al., 2014]] ). Increases in four bioregions were correlated to increasing temperature and decreasing precipitation. Decreases in burned area occurred despite increased temperature and decreased precipitation. Analyses of climate across Australia from 1950 to 2017 ( [[#Dowdy--2018|Dowdy, 2018]] ; [[#Harris--2019|Harris and Lucas, 2019]] ) and during periods with extensive fires in 2017 in eastern Australia ( [[#Hope--2019|Hope et al., 2019]] ), in 2018 in northeastern Australia ( [[#Lewis--2020|Lewis et al., 2020]] ), and in period 2019–2020 in southeastern Australia ( [[#Abram--2021|Abram et al., 2021]] ; [[#van%20Oldenborgh--2021|van Oldenborgh et al., 2021]] ) indicate that temperature and drought extremes due to the ENSO, Southern Annular Mode and other natural inter-decadal cycles drive inter-annual variability of fire weather. While the effects of inter-decadal climate cycles on fire are superimposed on long-term climate change, the relative importance of anthropogenic climate change in explaining changes in burned area in Australia remains unquantified ( ''medium evidence'' , ''high agreement'' ).

In Africa, the rate of change of burned area on the continent as a whole ranged from a non-statistically significant −0.45% yr -1 in the period 2002–2016 ( [[#Zubkova--2019|Zubkova et al., 2019]] ) to a significant −1.9% yr -1 in the period 2001–2016 ( [[#Wei--2020|Wei et al., 2020]] ). These decreases coincided with areas of agricultural expansion or areas where drought reduced fuel loads ( [[#Zubkova--2019|Zubkova et al., 2019]] ; [[#Wei--2020|Wei et al., 2020]] ). It is possible, however, that the 500-m spatial resolution of Modis remote-sensing fire data underestimates the area burned in Africa by half, by missing small fires ( [[#Ramo--2021|Ramo et al., 2021]] ). In the Serengeti-Mara savanna of east Africa, burned area showed no significant change from 2001 to 2014, although an increase in domestic livestock would tend to reduce the grass cover that fuels savanna fires ( [[#Probert--2019|Probert et al., 2019]] ).

In Mediterranean Europe, the area burned in the region as a whole decreased from 1985 to 2011 ( [[#Turco--2016|Turco et al., 2016]] ), although the burned area for Spain did not show a significant long-term increase from 1968 to 2010 ( [[#Moreno--2014|Moreno et al., 2014]] ) whereas that for Portugal in 2017 was the highest in the period 1980–2017 ( [[#Turco--2019|Turco et al., 2019]] ). Increased summer maximum temperature and decreased soil moisture explained most of the burned area observed, suggesting a contribution of climate change, but fire suppression, fire prevention, agricultural abandonment and reforestation as well as the reduction in forest area exerted even stronger influences on burned area than the climate across Mediterranean Europe ( ''robust evidence'' , ''high agreement'' ) ( [[#Moreno--2014|Moreno et al., 2014]] ; [[#Turco--2017|Turco et al., 2017]] ; [[#Viedma--2018|Viedma et al., 2018]] ; [[#Turco--2019|Turco et al., 2019]] ).

In the Arctic tundra and boreal forest, where wildfire has naturally been infrequent, burned area showed statistically significant increases of ~50% yr -1 across Siberia, Russia, from 1996 to 2015 ( [[#Ponomarev--2016|Ponomarev et al., 2016]] ) and 2% yr -1 across Canada from 1959 to 2015 ( [[#Hanes--2019|Hanes et al., 2019]] ). Wildfire burned ~6% of the area of four extensive Arctic permafrost regions in Alaska, USA, eastern Canada and Siberia from 1999 to 2014 ( [[#Nitze--2018|Nitze et al., 2018]] ). In boreal forest in the Northwest Territories, Canada and Alaska, USA, the area burned by wildfire increased at a statistically significant rate of 6.8% yr -1 in the period 1975–2015, ( [[#Veraverbeke--2017|Veraverbeke et al., 2017]] ), with smouldering below-ground fires that lasted through the winter covering ~1% of burned area in the period 2002–2016 ( [[#Scholten--2021|Scholten et al., 2021]] ). While burned area was correlated with temperature and reduced precipitation in Siberia ( [[#Ponomarev--2016|Ponomarev et al., 2016]] ; [[#Masrur--2018|Masrur et al., 2018]] ) and correlated with lightning, temperature and precipitation in the Northwest Territories and Alaska ( [[#Veraverbeke--2017|Veraverbeke et al., 2017]] ), no attribution analyses have examined relative influences of climate and non-climate factors.

In Indonesia, deforestation and draining of peat swamp forests dries out the peat, providing substantial fuel for fires ( [[#Page--2016|Page and Hooijer, 2016]] ). Extreme fire years in Indonesia, including 1997, 2006 and 2015, coincided with extreme heat and aridity during the warm phase of the ENSO ( [[#Field--2016|Field et al., 2016]] ). Fire-resistant forest in 2019 covered only 3% of peatlands and 4.5% of non-peatlands on Sumatra and Kalimantan ( [[#Nikonovas--2020|Nikonovas et al., 2020]] ).

In Chile, the area burned in the summer of 2016–2017 was 14 times the mean for the period 1985–2016 and the highest on record ( [[#Bowman--2019|Bowman et al., 2019]] ). While this extreme fire year coincided with the highest daily mean maximum temperature in the period 1979–2017 ( [[#Bowman--2019|Bowman et al., 2019]] ) in central Chile (the area of highest fire activity), burned area from 1976 to 2013 showed the highest correlation with the precipitation cycles of the ENSO and the temperature cycles of the Antarctic Oscillation ( [[#Urrutia-Jalabert--2018|Urrutia-Jalabert et al., 2018]] ).

Overall, burned area has increased in the Amazon, Arctic, Australia and parts of Africa and Asia, consistent with, but not formally attributed to anthropogenic climate change ( ''medium evidence'' , ''high agreement'' ). Deforestation, peat draining, agricultural expansion or abandonment, fire suppression and inter-decadal cycles such as the ENSO exert a stronger influence than climate change on wildfire trends in numerous regions outside of North America ( ''high confidence'' ).

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