Arctic land is characterized by a high surface and subsurface heterogeneity on different scales. However, the effects of land surface model resolution on fluxes and soil state variables in the Arctic have never been systematically studied, even though smaller scale heterogeneities are resolved in high-resolution land boundary condition datasets. Here, we compare 210 km and 5 km setups of the land surface model JSBACH3 for an idealized case study in eastern Siberia to investigate the effects of high versus low-resolution land boundary conditions on simulating the interactions of soil physics, hydrology and vegetation. We show for the first time that there are differences in the spatial averages of the simulated fluxes and soil state variables between resolution setups. Most differences are small in the summer mean, but larger within individual months. Heterogeneous soil properties induce large parts of the differences while vegetation characteristics play a minor role. Active layer depth shows a statistically significant increase of +20% in the 5 km setup relative to the 210 km setup for the summer mean and +43% for August. The differences are due to the nonlinear vertical discretization of the soil column amplifying the impact of the heterogeneous distributions of soil organic matter content and supercooled water. Resolution-induced differences in evaporation fluxes amount to +43% in July and are statistically significant. Our results show that spatial resolution significantly affects model outcomes due to nonlinear processes in heterogenous land surfaces. This suggests that resolution needs to be accounted in simulations of land surface models in the Arctic.

Spin-up is essential to provide initial conditions for land surface models (LSM) when they cannot be given reliably as in the application to regional permafrost change studies. In this study, the impacts of spin-up strategy including total spin-up length and cycling scheme on modeling of permafrost dynamics on the Qinghai-Tibet Plateau (QTP) were evaluated through two groups of experiments using a modified Noah LSM. The first group aims to test different total spin-up lengths and the second group for different cycling schemes. The results show that the presence of permafrost prolongs the convergence of the model. Vertically, the slowest convergence is observed at the permafrost table. The insufficiency of total spin-up length is prone to underestimate permafrost area and overestimate the degradation rate. Different cycling schemes considerably affect the resulting initial thermal fields and result in degradation rates with a difference of 3.37 x 10(3) km(2)/a on the QTP, which exceeds the difference (2.92 x 10(3) km(2)/a) in the degradation rates reported in existing studies. The multi-year cycling scheme is generally preferred, but overlong cycle length should be avoided to prevent the introduction of climate change trends in the spin-up period. We recommend a spin-up strategy of a 500-year cycling with the first 5- to 10-year of forcing for modeling permafrost on the QTP with the Noah LSM. Our findings highlight the importance of the spin-up strategy, which is usually neglected in present LSM-based permafrost modeling studies.