title: Including hydrological self-regulating processes in peatland models: Effects on peatmoss drought projections.
abstract: The water content of the topsoil is one of the key factors controlling biogeochemical processes, greenhouse gas emissions and biosphere - atmosphere interactions in many ecosystems, particularly in northern peatlands. In these wetland ecosystems, the water content of the photosynthetic active peatmoss layer is crucial for ecosystem functioning and carbon sequestration, and is sensitive to future shifts in rainfall and drought characteristics. Current peatland models differ in the degree in which hydrological feedbacks are included, but how this affects peatmoss drought projections is unknown. The aim of this paper was to systematically test whether the level of hydrological detail in models could bias projections of water content and drought stress for peatmoss in northern peatlands using downscaled projections for rainfall and potential evapotranspiration in the current (1991-2020) and future climate (2061-2090). We considered four model variants that either include or exclude moss (rain)water storage and peat volume change, as these are two central processes in the hydrological self-regulation of peatmoss carpets. Model performance was validated using field data of a peatland in northern Sweden. Including moss water storage as well as peat volume change resulted in a significant improvement of model performance, despite the extra parameters added. The best performance was achieved if both processes were included. Including moss water storage and peat volume change consistently reduced projected peatmoss drought frequency with >50%, relative to the model excluding both processes. Projected peatmoss drought frequency in the growing season was 17% smaller under future climate than current climate, but was unaffected by including the hydrological self-regulating processes. Our results suggest that ignoring these two fine-scale processes important in hydrological self-regulation of northern peatlands will have large consequences for projected climate change impact on ecosystem processes related to topsoil water content, such as greenhouse gas emissions.
authors.affiliation: Wageningen University, Plant Ecology and Nature Conservation Group, Wageningen, The Netherlands; Wageningen University, Soil Physics and Land Management Group, Wageningen, The Netherlands; Wageningen University, Soil Geography and Landscape Group, Wageningen, The Netherlands. Electronic address: jelmer.nijp@wur.nl.
authors.forename: Jelmer J
authors.initials: JJ
authors.lastname: Nijp
authors.affiliation: Wageningen University, Soil Physics and Land Management Group, Wageningen, The Netherlands. Electronic address: klaas.metselaar@wur.nl.
authors.forename: Klaas
authors.initials: K
authors.lastname: Metselaar
authors.affiliation: Wageningen University, Plant Ecology and Nature Conservation Group, Wageningen, The Netherlands. Electronic address: juul.limpens@wur.nl.
authors.forename: Juul
authors.initials: J
authors.lastname: Limpens
authors.affiliation: Uppsala University, Department of Earth Sciences, Uppsala, Sweden. Electronic address: claudia.teutschbein@geo.uu.se.
authors.forename: Claudia
authors.initials: C
authors.lastname: Teutschbein
authors.affiliation: Swedish University of Agricultural Sciences, Department of Forest Ecology and Management, Umeå, Sweden. Electronic address: matthias.peichl@slu.se.
authors.forename: Matthias
authors.initials: M
authors.lastname: Peichl
authors.affiliation: Swedish University of Agricultural Sciences, Department of Forest Ecology and Management, Umeå, Sweden. Electronic address: mats.b.nilsson@slu.se.
authors.forename: Mats B
authors.initials: MB
authors.lastname: Nilsson
authors.affiliation: Wageningen University, Plant Ecology and Nature Conservation Group, Wageningen, The Netherlands. Electronic address: frank.berendse@wur.nl.
authors.forename: Frank
authors.initials: F
authors.lastname: Berendse
authors.affiliation: Wageningen University, Soil Physics and Land Management Group, Wageningen, The Netherlands; Monash University, School of Chemistry, Melbourne, Victoria 3800, Australia. Electronic address: sjoerd.vanderzee@wur.nl.
authors.forename: Sjoerd E A T M
authors.initials: SEATM
authors.lastname: van der Zee
keywords: Climate change; Drought; Ecohydrology; Model development; Moisture; Northern peatlands