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Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the BorealArctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 x 0.5 degrees grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 x 10(6) km(2) (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 x 10(6) km(2). Bog, fen, and permafrost bog were the most abundant wetland classes, covering similar to 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 x 10(6) km(2) (6 % of domain). Low-methane-emitting large lakes (>10 km(2)) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small (<0.1 km(2)) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval betwee, Funding Agencies|National Science and Engineering Research Council of Canada (NSERC)Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN-2016-04688]; Campus Alberta Innovates Program; ERCEuropean Research Council (ERC)European Commission [851181, 725546]; Helmholtz Impulse and Networking Fund; Gordon and Betty Moore FoundationGordon and Betty Moore Foundation [GBMF5439, 839]; Swedish Research Council VRSwedish Research Council [2016-04829]; Norwegian Research CouncilResearch Council of NorwayEuropean Commission [274711]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [201705268]; BMBF KoPf Synthesis projectFederal Ministry of Education & Research (BMBF) [03F0834B]; NASA Earth Science [NNH17ZDA001N]; NSF-EnvE [1928048]; Natural Sciences and Engineering Research Council of Canada (NSERC) through the Canada Research Chairs programNatural Sciences and Engineering Research Council of Canada (NSERC); National Aeronautics and Space Administration IDS program (NASA) [NNX17AK10G]; Environment and Climate Change Canada; Canadian Space AgencyCanadian Space Agency; Government of Alberta; Government of Saskatchewan; US Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; US Fish and Wildlife ServiceUS Fish & Wildlife Service; PEW Charitable Trusts; Canadian Boreal Initiative; Alberta-Pacific Forest Industries Inc.; Mistik Management Ltd.; Louisiana-Pacific; Forest Products Association of Canada; Weyerhaeuser; Lakeland Industry and Community; Encana; Imperial Oil; Devon Energy Corporation; Shell Canada Energy; Suncor Foundation; Treaty 8 Tribal Corporation ("Akaitcho"); Dehcho First Nations; NSF PLR Arctic System Science Research Networking Activities (RNA) Permafrost Carbon Network: Synthesizing Flux Observations for Benchmarking Model Projections of Permafrost Carbon Exchange [1931333]; Swedish Research Council FORMASSwedish Research CouncilSwedish Research Council Formas [2018-01794]; Na

Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the BorealArctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 x 0.5 degrees grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 x 10(6) km(2) (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 x 10(6) km(2). Bog, fen, and permafrost bog were the most abundant wetland classes, covering similar to 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 x 10(6) km(2) (6 % of domain). Low-methane-emitting large lakes (>10 km(2)) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small (<0.1 km(2)) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval betwee, Funding Agencies|National Science and Engineering Research Council of Canada (NSERC)Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN-2016-04688]; Campus Alberta Innovates Program; ERCEuropean Research Council (ERC)European Commission [851181, 725546]; Helmholtz Impulse and Networking Fund; Gordon and Betty Moore FoundationGordon and Betty Moore Foundation [GBMF5439, 839]; Swedish Research Council VRSwedish Research Council [2016-04829]; Norwegian Research CouncilResearch Council of NorwayEuropean Commission [274711]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [201705268]; BMBF KoPf Synthesis projectFederal Ministry of Education & Research (BMBF) [03F0834B]; NASA Earth Science [NNH17ZDA001N]; NSF-EnvE [1928048]; Natural Sciences and Engineering Research Council of Canada (NSERC) through the Canada Research Chairs programNatural Sciences and Engineering Research Council of Canada (NSERC); National Aeronautics and Space Administration IDS program (NASA) [NNX17AK10G]; Environment and Climate Change Canada; Canadian Space AgencyCanadian Space Agency; Government of Alberta; Government of Saskatchewan; US Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; US Fish and Wildlife ServiceUS Fish & Wildlife Service; PEW Charitable Trusts; Canadian Boreal Initiative; Alberta-Pacific Forest Industries Inc.; Mistik Management Ltd.; Louisiana-Pacific; Forest Products Association of Canada; Weyerhaeuser; Lakeland Industry and Community; Encana; Imperial Oil; Devon Energy Corporation; Shell Canada Energy; Suncor Foundation; Treaty 8 Tribal Corporation ("Akaitcho"); Dehcho First Nations; NSF PLR Arctic System Science Research Networking Activities (RNA) Permafrost Carbon Network: Synthesizing Flux Observations for Benchmarking Model Projections of Permafrost Carbon Exchange [1931333]; Swedish Research Council FORMASSwedish Research CouncilSwedish Research Council Formas [2018-01794]; Na

Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the BorealArctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 x 0.5 degrees grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 x 10(6) km(2) (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 x 10(6) km(2). Bog, fen, and permafrost bog were the most abundant wetland classes, covering similar to 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 x 10(6) km(2) (6 % of domain). Low-methane-emitting large lakes (>10 km(2)) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small (<0.1 km(2)) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval betwee, Funding Agencies|National Science and Engineering Research Council of Canada (NSERC)Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN-2016-04688]; Campus Alberta Innovates Program; ERCEuropean Research Council (ERC)European Commission [851181, 725546]; Helmholtz Impulse and Networking Fund; Gordon and Betty Moore FoundationGordon and Betty Moore Foundation [GBMF5439, 839]; Swedish Research Council VRSwedish Research Council [2016-04829]; Norwegian Research CouncilResearch Council of NorwayEuropean Commission [274711]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [201705268]; BMBF KoPf Synthesis projectFederal Ministry of Education & Research (BMBF) [03F0834B]; NASA Earth Science [NNH17ZDA001N]; NSF-EnvE [1928048]; Natural Sciences and Engineering Research Council of Canada (NSERC) through the Canada Research Chairs programNatural Sciences and Engineering Research Council of Canada (NSERC); National Aeronautics and Space Administration IDS program (NASA) [NNX17AK10G]; Environment and Climate Change Canada; Canadian Space AgencyCanadian Space Agency; Government of Alberta; Government of Saskatchewan; US Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; US Fish and Wildlife ServiceUS Fish & Wildlife Service; PEW Charitable Trusts; Canadian Boreal Initiative; Alberta-Pacific Forest Industries Inc.; Mistik Management Ltd.; Louisiana-Pacific; Forest Products Association of Canada; Weyerhaeuser; Lakeland Industry and Community; Encana; Imperial Oil; Devon Energy Corporation; Shell Canada Energy; Suncor Foundation; Treaty 8 Tribal Corporation ("Akaitcho"); Dehcho First Nations; NSF PLR Arctic System Science Research Networking Activities (RNA) Permafrost Carbon Network: Synthesizing Flux Observations for Benchmarking Model Projections of Permafrost Carbon Exchange [1931333]; Swedish Research Council FORMASSwedish Research CouncilSwedish Research Council Formas [2018-01794]; Na

Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the BorealArctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 x 0.5 degrees grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 x 10(6) km(2) (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 x 10(6) km(2). Bog, fen, and permafrost bog were the most abundant wetland classes, covering similar to 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 x 10(6) km(2) (6 % of domain). Low-methane-emitting large lakes (>10 km(2)) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small (<0.1 km(2)) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval betwee, Funding Agencies|National Science and Engineering Research Council of Canada (NSERC)Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN-2016-04688]; Campus Alberta Innovates Program; ERCEuropean Research Council (ERC)European Commission [851181, 725546]; Helmholtz Impulse and Networking Fund; Gordon and Betty Moore FoundationGordon and Betty Moore Foundation [GBMF5439, 839]; Swedish Research Council VRSwedish Research Council [2016-04829]; Norwegian Research CouncilResearch Council of NorwayEuropean Commission [274711]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [201705268]; BMBF KoPf Synthesis projectFederal Ministry of Education & Research (BMBF) [03F0834B]; NASA Earth Science [NNH17ZDA001N]; NSF-EnvE [1928048]; Natural Sciences and Engineering Research Council of Canada (NSERC) through the Canada Research Chairs programNatural Sciences and Engineering Research Council of Canada (NSERC); National Aeronautics and Space Administration IDS program (NASA) [NNX17AK10G]; Environment and Climate Change Canada; Canadian Space AgencyCanadian Space Agency; Government of Alberta; Government of Saskatchewan; US Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; US Fish and Wildlife ServiceUS Fish & Wildlife Service; PEW Charitable Trusts; Canadian Boreal Initiative; Alberta-Pacific Forest Industries Inc.; Mistik Management Ltd.; Louisiana-Pacific; Forest Products Association of Canada; Weyerhaeuser; Lakeland Industry and Community; Encana; Imperial Oil; Devon Energy Corporation; Shell Canada Energy; Suncor Foundation; Treaty 8 Tribal Corporation ("Akaitcho"); Dehcho First Nations; NSF PLR Arctic System Science Research Networking Activities (RNA) Permafrost Carbon Network: Synthesizing Flux Observations for Benchmarking Model Projections of Permafrost Carbon Exchange [1931333]; Swedish Research Council FORMASSwedish Research CouncilSwedish Research Council Formas [2018-01794]; Na

Methane emissions from boreal and arctic wetlands, lakes, and rivers are expected to increase in response to warming and associated permafrost thaw. However, the lack of appropriate land cover datasets for scaling field-measured methane emissions to circumpolar scales has contributed to a large uncertainty for our understanding of present-day and future methane emissions. Here we present the BorealArctic Wetland and Lake Dataset (BAWLD), a land cover dataset based on an expert assessment, extrapolated using random forest modelling from available spatial datasets of climate, topography, soils, permafrost conditions, vegetation, wetlands, and surface water extents and dynamics. In BAWLD, we estimate the fractional coverage of five wetland, seven lake, and three river classes within 0.5 x 0.5 degrees grid cells that cover the northern boreal and tundra biomes (17 % of the global land surface). Land cover classes were defined using criteria that ensured distinct methane emissions among classes, as indicated by a co-developed comprehensive dataset of methane flux observations. In BAWLD, wetlands occupied 3.2 x 10(6) km(2) (14 % of domain) with a 95 % confidence interval between 2.8 and 3.8 x 10(6) km(2). Bog, fen, and permafrost bog were the most abundant wetland classes, covering similar to 28 % each of the total wetland area, while the highest-methane-emitting marsh and tundra wetland classes occupied 5 % and 12 %, respectively. Lakes, defined to include all lentic open-water ecosystems regardless of size, covered 1.4 x 10(6) km(2) (6 % of domain). Low-methane-emitting large lakes (>10 km(2)) and glacial lakes jointly represented 78 % of the total lake area, while high-emitting peatland and yedoma lakes covered 18 % and 4 %, respectively. Small (<0.1 km(2)) glacial, peatland, and yedoma lakes combined covered 17 % of the total lake area but contributed disproportionally to the overall spatial uncertainty in lake area with a 95 % confidence interval betwee, Funding Agencies|National Science and Engineering Research Council of Canada (NSERC)Natural Sciences and Engineering Research Council of Canada (NSERC) [RGPIN-2016-04688]; Campus Alberta Innovates Program; ERCEuropean Research Council (ERC)European Commission [851181, 725546]; Helmholtz Impulse and Networking Fund; Gordon and Betty Moore FoundationGordon and Betty Moore Foundation [GBMF5439, 839]; Swedish Research Council VRSwedish Research Council [2016-04829]; Norwegian Research CouncilResearch Council of NorwayEuropean Commission [274711]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [201705268]; BMBF KoPf Synthesis projectFederal Ministry of Education & Research (BMBF) [03F0834B]; NASA Earth Science [NNH17ZDA001N]; NSF-EnvE [1928048]; Natural Sciences and Engineering Research Council of Canada (NSERC) through the Canada Research Chairs programNatural Sciences and Engineering Research Council of Canada (NSERC); National Aeronautics and Space Administration IDS program (NASA) [NNX17AK10G]; Environment and Climate Change Canada; Canadian Space AgencyCanadian Space Agency; Government of Alberta; Government of Saskatchewan; US Forest ServiceUnited States Department of Agriculture (USDA)United States Forest Service; US Fish and Wildlife ServiceUS Fish & Wildlife Service; PEW Charitable Trusts; Canadian Boreal Initiative; Alberta-Pacific Forest Industries Inc.; Mistik Management Ltd.; Louisiana-Pacific; Forest Products Association of Canada; Weyerhaeuser; Lakeland Industry and Community; Encana; Imperial Oil; Devon Energy Corporation; Shell Canada Energy; Suncor Foundation; Treaty 8 Tribal Corporation ("Akaitcho"); Dehcho First Nations; NSF PLR Arctic System Science Research Networking Activities (RNA) Permafrost Carbon Network: Synthesizing Flux Observations for Benchmarking Model Projections of Permafrost Carbon Exchange [1931333]; Swedish Research Council FORMASSwedish Research CouncilSwedish Research Council Formas [2018-01794]; Na