Near-surface ground ice map of the Northern Hemisphere

The functioning and vulnerability of permafrost are largely determined by near-surface ground ice content. However, high-quality, grid-based ground ice maps for the Northern Hemisphere are currently unavailable. This study presents the first 1-km resolution grid-based ground ice map within 5 m below the permafrost table across the Northern Hemisphere. The map integrates an unprecedented amount (1178 boreholes) of field measurement for volumetric ice content (VIC) and multisource geospatial data, especially paleoclimate, remote sensing data, and surficial geology units, using Copula-Embedded Bayesian Model Averaging (COP-BMA) techniques with multiple machine learning models and 200 ensemble simulations. The validation indicates relatively low errors (R² = 0.86, RMSE = 7.08%VIC, bias = 0.02%VIC), while the uncertainty, represented by the 95% prediction interval (PI), is 16.08% ± 3.55%VIC. The map indicates that the total ice storage of near-surface permafrost across the Northern Hemisphere is approximately 54,600 km³ (47,800-62,300 km³), about twice the value from the International Permafrost Association map. This difference may be due to, but is not limited to, advancements in mapping techniques, the integration of additional measurement data, and improved spatial resolution. High VIC (>80%) is predominantly concentrated in low-lying plains, wetlands, and marshes. In contrast, mountainous regions, including the Qinghai-Xizang Plateau and Mongolian Plateau, exhibit lower VIC, typically ranging from 20% to 40%. The new ground ice map exhibits a spatial pattern that is largely consistent with previous maps while providing enhanced spatial detail. This high-resolution map serves as a benchmark for tracing permafrost changes and assessing impacts on climate, hydrology, ecosystems, and infrastructure in permafrost regions.