Increasing contribution of peatlands to boreal evapotranspiration in a warming climate

Abstract

The response of evapotranspiration (ET) to warming is of critical importance to the water and carbon cycle of the boreal biome, a mosaic of land cover types dominated by forests and peatlands. The effect of warming-induced vapour pressure deficit (VPD) increases on boreal ET remains poorly understood because peatlands are not specifically represented as plant functional types in Earth system models. Here we show that peatland ET increases more than forest ET with increasing VPD using observations from 95 eddy covariance tower sites. At high VPD of more than 2 kPa, peatland ET exceeds forest ET by up to 30%. Future (2091–2100) mid-growing season peatland ET is estimated to exceed forest ET by over 20% in about one-third of the boreal biome for RCP4.5 and about two-thirds for RCP8.5. Peatland-specific ET responses to VPD should therefore be included in Earth system models to avoid biases in water and carbon cycle projections.

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Fig. 1: Multimodel mean projection of changes in growing season ΔVPDGS by the end of the twenty-first century.
Fig. 2: Eddy covariance flux tower locations and spatial pattern of dryness index in the boreal biome.
Fig. 3: ET and gs response to VPD.
Fig. 4: A comparison of peatland and forest ET under current and future climates.

Data availability

Source data for Figs. 1–4 and Extended Data Figs. 1–3 are provided with the paper. Eddy covariance flux tower data used in this study can be accessed through the AmeriFlux (https://ameriflux.lbl.gov/), FLUXNET (https://fluxnet.fluxdata.org/data/fluxnet2015-dataset/), or European Fluxes Database Cluster (http://www.europe-fluxdata.eu/) webpages (see Supplementary Data). Site data that are not accessible through these webpages (see Supplementary Data) are available from the corresponding author on request. Monthly climate data and PET can be accessed through the East Anglia Climate Research Unit webpage (https://crudata.uea.ac.uk/cru/data/hrg/cru_ts_4.02/). Most CMIP5 model output is archived and made available through the Earth System Grid Federation (https://esgf.llnl.gov/). CanESM2 model output can be downloaded through the Canadian Centre for Climate Modelling and Analysis (http://climate-modelling.canada.ca/data/cgcm4/CanESM2/index.shtml) and CESM1-CAM5 model output is available through the Climate Data Gateway at the National Center for Atmospheric Research (https://www.earthsystemgrid.org/). Peatland maps are freely available through the Research Data Leeds Repository (http://archive.researchdata.leeds.ac.uk/251/) and on request from the corresponding author. MODIS data can be accessed for all flux tower sites through the Global Subset Tool: MODIS/VIIRS Products (https://modis.ornl.gov/cgi-bin/MODIS/global/subset.pl). The global FLUXCOM land-atmosphere energy flux data product can be accessed through the FLUXCOM webpage (http://www.fluxcom.org/EF-Products/). Global monthly mean LAI climatology can be accessed through the ORNL Distributed Active Archive Center for Biogeochemical Dynamics (https://daac.ornl.gov/VEGETATION/guides/Mean_Seasonal_LAI.html).

Code availability

All MATLAB code used in this study is available through the corresponding author’s GitHub repository72 (https://github.com/manuelhelbig/BWF_Synthesis; https://doi.org/10.5281/zenodo.3653056) and is available from the corresponding author on request. The software used to generate all results is MATLAB 2016a.

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Acknowledgements

The research published in this paper is part of the project titled Boreal Water Futures, which is funded by the Global Water Futures programme of the Canada First Research Excellence Fund; additional information is available at www.globalwaterfutures.ca. We thank all the eddy covariance flux tower teams for sharing their data and we are grateful to the ESM groups for providing their model output through CMIP5. We thank the World Climate Research Programme’s Working Group on Coupled Modelling for leading the CMIP. We acknowledge the research group that made the peatland map freely available and we thank E. Chan (ECCC) for processing the shapefile PEATMAP to a raster map. We are grateful to E. Sahlée and A. Rutgersson for providing lake eddy covariance data to an earlier version of the manuscript, T. Zivkovic and S. Davidson for insightful feedback, and M. Khomik, A. Green, E. Kessel, G. Drewitt, P. Kolari and M. Provenzale for helping with data preparation. I.M. acknowledges funding from ICOS-FINLAND (grant no. 281255), the Finnish Center of Excellence (grant no. 307331) and the EU Horizon 2020 RINGO project (grant no. 730944). A.P. acknowledges funding through the research project no. 18–05–60203-Arktika (RFBR and Government of Krasnoyarsk Territory, Krasnoyarsk Regional Fund of Science) and support for flux tower sites RU-ZOP and RU-ZOB through the Max Planck Society. A.D. and J.T. acknowledge funding from US National Science foundation (grant no. DEB-1440297) and a DOE Ameriflux Network Management Project award to the ChEAS core site cluster. T.A.B., A.G.B. and R.J. acknowledge support received through grants from the Fluxnet Canada ResearchNetwork (2002–2007; NSERC, CFCAS and BIOCAP) and the Canadian Carbon Program (2008–2012; CFCAS) and by an NSERC (Climate Change and Atmospheric Research) grant to the Changing Cold Regions Network (CCRN; 2012–2016) and an NSERC Discovery Grant. H. I. and M. U. acknowledge support by the Arctic Challenge for Sustainability (ArCS) project. J.K. and A.V. acknowledge funding from RFBR project no. 19–04–01234-a. B.A. acknowledges funding through NASA, NSERC, BIOCAP Canada, the Canadian Foundation for Climate and Atmospheric Sciences and the Canadian Foundation for Innovation for flux measurements at CA-MAN and through the Canadian Forest Service, the Natural Sciences and Engineering Research Council of Canada (NSERC), the FLUXNET-Canada Network (NSERC, the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS) and BIOCAP Canada), the Canadian Carbon Program (CFCAS), Parks Canada, the Program of Energy Research and Development (PERD), and Action Plan 2000 for flux measurements at CA-SF1, CA-SF2 and CA-SF3. M.B.N, M.O.L, M.P. and J.C. gratefully acknowledge funding from the Swedish research infrastructures SITES and ICOS Sweden and research grants from Kempe Foundations, (grant no. SMK-1743); VR (grant no. 2018–03966) and Formas, (grant no. 2016–01289) and M.P. gratefully acknowledges funding from Knut and Alice Wallenberg Foundation (grant no. 2015.0047). M.W. and I.F. acknowledge funding by the German Research Foundation (grant no. Wi 2680/2–1) and the European Union (grant no. 36993). B.R. and L.K. acknowledge support by the Cluster of Excellence ‘CliSAP’ (EXC177) of the University of Hamburg, funded by the German Research Foundation. O.S. acknowledges funding by the Canada Research Chairs, Canada Foundation for Innovation Leaders Opportunity Fund, and Natural Sciences and Engineering Research Council Discovery Grant Programs. H.I. acknowledges JAMSTEC and IARC/UAF collaboration study (JICS) and Arctic Challenge for Sustainability Project (ArCS).

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Contributions

M.H. and J.M.W. designed the study. M.H., J.M.W. and J.R.M. developed the methodology. J.M.W., P.A., B.A., M.A., A.G.B., T.A.B., P.D.B., S.K.C, J.Chen, J.Chi, A.R.D., A.D., E.E., T.F., L.B.F., I.F., A.G., S.H., M.H., E.R.H., H.Ikawa, H.Iwata, P.-E.I., R.J., J.K., M.K., L.K., A.Lindroth, T.O., M.O.L., A.Lohila, T.M., I.M., P.M., P.A.M., D.F.N., E.M.N., M.B.N., M.P., R.M.P., R.P., A.P., W.L.Q., N.T.R., D.E.R., B.R.K.R., O.S., I.B.S., P.T., E.-S.T., J.-P.T., J.T., M.U., A.V., M.W., S.W. and V.Z. contributed eddy covariance flux data. M.H. analysed the data and wrote the first draft. All authors contributed to data interpretation and commented on the manuscript at all stages.

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Correspondence to Manuel Helbig.

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Extended data

Extended Data Fig. 1 Anomalies of growing season (May-September) mean daily maximum vapour pressure deficit (VPDGS) for the boreal biome (circles, relative to the mean of 1981–2010).

The solid line shows five-year running mean. VPDGS is derived from the University of East Anglia Climate Research Unit [CRU] TS v4.03 dataset (Methods) and boreal biome grid cells are identified based on ref. 59. Source data

Extended Data Fig. 2

Relationship between observed half-hourly afternoon (15h-18h) evaporative fraction and vapour pressure deficit for forest and peatland sites during the growing season. Shaded areas show standard errors. Source data

Extended Data Fig. 3

Probability density function (PDF, solid lines) of observed growing season (May- September) forest (n = 305 growing seasons) and peatland (n = 122 growing seasons) evapotranspiration. Dashed lines show median growing season evapotranspiration. Source data

Supplementary information

Supplementary Information

Supplementary Data 1

List of eddy covariance flux tower sites used in this study, including metadata for each site.

Source data

Source Data Fig. 1

Projected changes in vapour pressure deficit in the boreal biome.

Source Data Fig. 2

Dryness index map and flux tower site locations.

Source Data Fig. 3

VPD-ET/gs response curve data.

Source Data Fig. 4

Map of current and projected ratios of peatland versus forest ET.

Source Data Extended Data Fig. 1

VPD anomaly data for the boreal biome.

Source Data Extended Data Fig. 2

VPD-evaporative fraction response curve data.

Source Data Extended Data Fig. 3

Growing season ET data for boreal peatlands and forests.

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Helbig, M., Waddington, J.M., Alekseychik, P. et al. Increasing contribution of peatlands to boreal evapotranspiration in a warming climate. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0763-7

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