Wet tundra polygon centers and distance between polygon centroids on Samoylov Island, Lena Delta, Siberia, Russia, with links to shape files

Subgrid processes occur in various ecosystems and landscapes but, because of their small scale, they are not represented or poorly parameterized in climate models. These local heterogeneities are often important or even fundamental for energy and carbon balances. This is especially true for northern peatlands and in particular for the polygonal tundra, where methane emissions are strongly influenced by spatial soil heterogeneities. We present a stochastic model for the surface topography of polygonal tundra using Poisson–Voronoi diagrams and we compare the results with available recent field studies. We analyze seasonal dynamics of water table variations and the landscape response under different scenarios of precipitation income. We upscale methane fluxes by using a simple idealized model for methane emission. Hydraulic interconnectivities and large-scale drainage may also be investigated through percolation properties and thresholds in the Voronoi graph. The model captures the main statistical characteristics of the landscape topography, such as polygon area and surface properties as well as the water balance. This approach enables us to statistically relate large-scale properties of the system to the main small-scale processes within the single polygons.

次网格过程（subgrid process）广泛存在于各类生态系统与景观之中，但由于其尺度极小，在气候模型中往往未被表征，或是参数化程度不足。此类局地非均质性通常对能量与碳平衡至关重要，甚至具有基础性作用。这一点在北方泥炭地，尤其是多边形苔原（polygonal tundra）中尤为显著：该区域的甲烷排放深受土壤空间非均质性的调控。本研究基于泊松-沃罗诺伊图（Poisson–Voronoi diagrams）构建了多边形苔原地表地形的随机模型，并将模拟结果与已发表的最新实地研究数据进行对比。我们分析了不同降水情景下地下水位变化的季节动态，以及景观的响应特征，并通过构建简化的理想化甲烷排放模型实现了甲烷通量的尺度上推。此外，还可借助沃罗诺伊图（Voronoi graph）中的渗流特性与临界阈值，探究水力连通性与大规模排水过程。该模型能够准确复现景观地形的主要统计特征，包括多边形面积、地表属性以及水量平衡。该方法使得我们能够通过统计分析，将系统的大尺度属性与单个多边形内部的核心小尺度过程建立关联。