Improving the simulation of permafrost extent by representing the multi-tiling energy budgets in ORCHIDEE-MICT model

The surface energy budget plays a critical role in terrestrial hydrologic and biogeochemical cycles. Nevertheless, its highly spatial heterogeneity across different vegetation types is still missing in the land surface model, ORCHIDEE-MICT (ORganizing Carbon and Hydrology in Dynamic EcosystEms–aMeliorated Interactions between Carbon and Temperature). In this study, we describe the representation of a multi-tiling energy budget in ORCHIDEE-MICT and assess its short and long-term impacts on energy, hydrology, and carbon processes. We found that: 1) With the specific values of surface properties for each vegetation type, the new version presents warmer surface and soil temperatures, wetter soil moisture, and increased soil organic carbon storage across the Northern Hemisphere. 2) Despite reproducing the absolute values and spatial gradients of surface and soil temperatures from satellite and in-situ observations, the considerable uncertainties in simulated soil organic carbon and hydrologic processes prevent an obvious improvement of temperature bias existing in the original ORCHIDEE-MICT. 3) The simulated continuous permafrost area (15.2 Mkm2) and non-continuous permafrost area (3.1 Mkm2) are comparative to observation-based datasets from Brown et al. (2002) (10.8 Mkm2 for continuous and 4.6 Mkm2 for non-continuous) and Obu et al. (2019) (11.5 Mkm2 for continuous and 5.3 Mkm2 for non-continuous). Consequently, the new version will facilitate various model-based permafrost studies in the future.