Abstract
Abstract. This study investigates and compares soil moisture and hydrology projections of broadly used land models with permafrost processes and highlights the causes and impacts of permafrost zone soil moisture projections. Climate models project warmer temperatures and increases in precipitation (P) which will intensify evapotranspiration (ET) and runoff in land models. However, this study shows that most models project a long-term drying of the surface soil (0–20 cm) for the permafrost region despite increases in the net air–surface water flux (P-ET). Drying is generally explained by infiltration of moisture to deeper soil layers as the active layer deepens or permafrost thaws completely. Although most models agree on drying, the projections vary strongly in magnitude and spatial pattern. Land models tend to agree with decadal runoff trends but underestimate runoff volume when compared to gauge data across the major Arctic river basins, potentially indicating model structural limitations. Coordinated efforts to address the ongoing challenges presented in this study will help reduce uncertainty in our capability to predict the future Arctic hydrological state and associated land–atmosphere biogeochemical processes across spatial and temporal scales.
Highlights
With increases in air temperature, models project an ensemble mean decrease of ∼ 13 000 000 km2 (91 %) of the permafrost domain by 2299 (Fig. 2b). Coincident with these changes, most models projected a long-term drying of the near-surface soils when averaged over the permafrost landscape (Fig. 2c)
To understand why models projected upper soil drying despite increases in the net precipitation (P -ET) into the soil, we examined whether or not increases in active-layer thickness (ALT) and/or the complete thaw of near-surface permafrost could be related to surface soil drying of the top 0– 20 cm ALT
We show that the timing and magnitude of projected soil moisture changes vary widely across models, pointing to an uncertain future in permafrost hydrology and associated climatic feedbacks
Summary
Hydrology plays a fundamental role in permafrost landscapes by modulating complex interactions among biogeochemical cycling (Frey and Mcclelland, 2009; Newman et al, 2015; Throckmorton et al, 2015), geomorphology (Grosse et al, 2013; Kanevskiy et al, 2017; Lara et al, 2015; Liljedahl et al, 2016), and ecosystem structure and function (Andresen et al, 2017; Avis et al, 2011; Oberbauer et al, 2007). Lawrence et al (2015) found that the impact of the soil drying projected in simulations with the Community Land Model decreased the overall global warming potential of the permafrost carbon–climate feedback by 50 %. The impact of soil moisture changes on the permafrost carbon feedback could be significant. This decrease was attributed to a much slower increase in CH4 emissions if surface soils dry, which is partially compensated for by a stronger increase in CO2 emissions under drier soil conditions
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