The biophysical climate mitigation potential of boreal peatlands during the growing season

Manuel Helbig ,B.d Amiro ,Elyn Humphreys ,Jiquan Chen ,Mika Korkiakoski ,Vyacheslav Zyrianov ,Pierre Taillardat ,William L Quinton ,Michelle Garneau ,Hiroyasu Iwata ,Pavel Alekseychik ,Eeva‐Stiina Tuittila ,Martin Wilmking ,Philip Marsh ,Mikaell Ottosson Löfvenius ,Erin M Nicholls ,Mika Aurela ,Ankur R Desai ,Masahito Ueyama ,Oliver Sonnentag ,Silvie Harder ,J M Waddington ,Takeshi Ohta ,Jinshu Chi ,Hiroki Ikawa ,Daniel F Nadeau ,Ivan Mammarella ,Lawrence B Flanagan ,Juha‐Pekka Tuovinen ,Matthias Peichl ,Thomas Friborg ,Annalea Lohila ,Alan G Barr ,Nigel T Roulet ,T Andrew Black ,Lars Kutzbach ,Juliya Kurbatova ,Rachhpal S Jassal ,Andrej Varlagin ,Achim Grelle ,Mats Nilsson ,I B Strachan ,Timo Vesala ,Paul A Moore ,Е Д Лапшина ,Sean K Carey ,Michal Heliasz ,Eugénie Euskirchen ,Pierre‐Érik Isabelle ,J Turner ,Anatoly Prokushkin ,Trofim C Maximov ,Anders Lindroth ,Allison L Dunn ,Richard M Petrone ,Benjamin R K Runkle ,Christopher Schulze

doi:10.1088/1748-9326/abab34

Abstract

Peatlands and forests cover large areas of the boreal biome and are critical for global climate regulation. They also regulate regional climate through heat and water vapour exchange with the atmosphere. Understanding how land-atmosphere interactions in peatlands differ from forests may therefore be crucial for modelling boreal climate system dynamics and for assessing climate benefits of peatland conservation and restoration. To assess the biophysical impacts of peatlands and forests on peak growing season air temperature and humidity, we analysed surface energy fluxes and albedo from 35 peatlands and 37 evergreen needleleaf forests—the dominant boreal forest type—and simulated air temperature and vapour pressure deficit (VPD) over hypothetical homogeneous peatland and forest landscapes. We ran an evapotranspiration model using land surface parameters derived from energy flux observations and coupled an analytical solution for the surface energy balance to an atmospheric boundary layer (ABL) model. We found that peatlands, compared to forests, are characterized by higher growing season albedo, lower aerodynamic conductance, and higher surface conductance for an equivalent VPD. This combination of peatland surface properties results in a ∼20% decrease in afternoon ABL height, a cooling (from 1.7 to 2.5 °C) in afternoon air temperatures, and a decrease in afternoon VPD (from 0.4 to 0.7 kPa) for peatland landscapes compared to forest landscapes. These biophysical climate impacts of peatlands are most pronounced at lower latitudes (∼45°N) and decrease toward the northern limit of the boreal biome (∼70°N). Thus, boreal peatlands have the potential to mitigate the effect of regional climate warming during the growing season. The biophysical climate mitigation potential of peatlands needs to be accounted for when projecting the future climate of the boreal biome, when assessing the climate benefits of conserving pristine boreal peatlands, and when restoring peatlands that have experienced peatland drainage and mining.

Highlights

Peatlands are found throughout the boreal biome and cover about 15% of the boreal land area (Xu et al 2018)
We address the question whether peatlandspecific biophysical land surface properties have the potential to mitigate climate warming regionally by creating cooler and more humid growing season climates compared to boreal forests
Differences in energy partitioning were reflected in significantly higher midday Bowen ratios for forests than for peatlands between March and September (figure 2(b))

Summary

Introduction

Peatlands are found throughout the boreal biome and cover about 15% of the boreal land area (Xu et al 2018). Peatlands are usually characterised by high evapotranspiration rates during the growing season if the water table depth remains close to the surface (Lafleur et al 2005), i.e. partitioning more available energy into latent heat (i.e. water vapor) than into sensible heat (Lafleur 2008). Using a panboreal evapotranspiration dataset, Helbig et al (2020) have shown that growing season evapotranspiration in boreal peatlands is higher than in boreal forests mainly due to higher surface conductance of peatlands. How such differences in land surface properties and surface energy fluxes may alter regional climates in the boreal biome remains uncertain. To assess the net climate mitigation potential of peatlands, both the biogeochemical and biophysical impacts need to be considered since biophysical climate impacts can either amplify or attenuate the magnitude of climate warming regionally (Pielke et al 2002)

Methods

Results

Conclusion