Assessing the Response of Blanket Peatlands to Climate Change Using the DigiBog Model and Winter's Concept of the “Hydrologic Landscape”

Peatlands are important global carbon stores, but it is unclear whether they will continue as carbon sinks under future climates, or degrade, leaking carbon to the atmosphere. We used the DigiBog peatland development model to explore this question for a blanket peatland in Glen Affric, Scotland, investigating how topography and climate have affected net peat accumulation across this complex landscape. DigiBog accurately captured spatial variation in measured modern peat thickness (Lin's Concordance Correlation Coefficient = 0.86). As expected, peat accumulated to greater depths in topographic basins compared to slopes and drainage divides over the Holocene. Simulations of the future suggest the study site will continue accumulating peat until 2100 CE under all Representative Concentration Pathways. However, DigiBog predicts greatest future peat accumulation away from basins, continuing a trend observed over the last c. 2000 years. We also tested Winter's (2000), https://doi.org/10.1111/j.1752-1688.2000.tb04269.x conceptual model, which proposes that wetland vulnerability to climate change depends on position in the hydrologic landscape, by comparing peat thickness with the Topographic Wetness Index. While correlations were moderate to strong, our finding of greater recent accumulation away from basins contradicts Winter's model's predictions. Additionally, DigiBog shows that thin (<40 cm) hillslope peats persisted throughout the Holocene despite drier climatic phases, rather than experiencing complete loss and re-establishment cycles. We conclude that process-based ecohydrological models like DigiBog can complement simpler modeling approaches and should be used when assessing rates and spatial patterns of peat accumulation and loss in response to 21st Century climate change.