Analysis of resolution-induced differences in soil - hydrology - vegetation interactions in the Arctic using state-of-the-art land surface model

Arctic permafrost degradation and carbon decomposition do not occur homogeneously across Arctic ecosystems due to the rich landscape diversity and the high amount of small-scale heterogeneities. Traditionally, Earth system models (ESM) are deployed to investigate future climate change in the northern permafrost areas. The typical heterogeneous landscape characteristics of the Arctic are however in scale well below the usual ESM resolutions of several hundred kilometers. To take in-depth account of small-scale heterogeneous landscapes, a higher land surface model resolution is advantageous.

To investigate whether and why resolution matters in simulating the interactions of soil physics, hydrology, and vegetation in the Arctic, we develop a high-resolution version of the land surface model (LSM) JSBACH3 on the scale of 5 km for a case study in the Chersky region in eastern Siberia. We then compare the results with the output of the same model in a low ESM resolution of about 200 km. The LSM simulations are performed in standalone mode (without feedbacks to climate) using the same climate forcing for both, high- and low- resolution setups. Our analysis shows that small-scale soil characteristics are more relevant regarding resolution than vegetation properties. We found that the formulation of supercooled water processes in the soil has a major impact on the differences between low and fine resolutions, as well as soil organic matter fractions. Other soil parameters such as hydraulic conductivity, soil porosity or heat conductivity have relatively minor effects on differences between model resolutions.

We show the relevance of model resolution in the simulation of Arctic land physical and biogeochemical interactions and thus argue that the development of a high-resolution pan-Arctic LSM would be a major advancement in modelling future Arctic permafrost and carbon projections.