Simulating the thermal behavior of northern peatlands with a 3‐D microtopography

Abstract

Globally, peatlands represent important stores of carbon which may have an important influence on future climatic conditions. Understanding how peatlands will influence, and also respond to, future climates will require an understanding of their thermal behavior. Peatland surfaces are often characterized by a 3‐D microtopography. Therefore, we might expect strong horizontal thermal gradients and exchanges between neighboring microforms with contrasting hydrological regimes and vegetation composition. However, previous peatland temperature models have assumed that horizontal temperature gradients are insignificant and that temperatures can be simulated adequately by applying 1‐D vertical models. We outline the development, parameterization, and evaluation of a 3‐D model that simulates peat temperatures in two microforms, a Sphagnum fuscum hummock surrounded by a Sphagnum magellanicum lawn, to identify the importance of such horizontal heat fluxes. The 3‐D Heat‐in‐Peat (HIP) model provides a reasonable representation of temperatures in the microforms with a root‐mean‐squared error between modeled and measured peat temperatures ranging from 2.33° to 0.20°C. The 3‐D HIP model highlights the importance of a 3‐D microtopography on the surface energy balance and peat temperatures. Comparison of the 3‐D HIP model with 1‐D simulations of peat temperatures shows that horizontal temperature gradients significantly influence peat temperatures within the hummock, with simulated temperatures at a depth of 0.375 m beneath the hummock being underestimated by up to 1.2°C in 1‐D simulations. In contrast, temperatures within the Sphagnum magellanicum lawn were adequately simulated by ignoring horizontal heat fluxes.