Modeled Subsidence of Permafrost Terrain 2025–2050: North‐Central Alaska

ABSTRACT A large fraction of the Alaska terrain is underlain by regolith that contains excess ice (ice that in volume exceeds the natural pore space). Possible loss of excess ice would lead to ground subsidence, which in turn would disturb and destabilize the ground surface. Depending on the volume fraction and local variations in excess ice content and soil properties, the subsidence would lead to forest disturbances, increased soil erosion, hydrological changes, and potential increase in sediment supply to rivers and creeks. In addition to InSAR annual evaluations, currently, the best available long‐term data of the ground subsidence come from historical observations (~20 years) on a few field sites of limited spatial extent in Alaska and Western Canada. Due to the projected changes of environmental conditions in Alaska in the coming decades, there is a reasonable expectation of widespread ground subsidence. To better understand the spatial variations and varying magnitudes of expected subsidence, we set out to model and map the future ground subsidence across north‐central Alaska, along the Dalton Highway corridor. We analyzed the current thermal regime on the dominant landcovers on various amounts of mapped excess soil ice. The in situ observations and the purpose‐built subsidence model, coupled with the existing landcover and excess ice maps and analytical projections under varying assumptions, allowed us to model the future ground subsidence by 2050. We run the model for two separate excess ice scenarios for north‐central Alaska: 50%, and 25% near surface excess ice guided by published map. The results show the projected average subsidence rates of 1.79–2.33 cm/year for 2025–2050 in the southern part (Yukon River area) of the study area for 25% and 50% excess ice, respectively, whereas the smallest projected subsidence rates of < 0.17 cm/year in the northern part (North Slope) of the study area. This broad variation is explained by the strong and persistent North–South climatic gradient. However, the small‐scale spatial variation in the subsidence, shown in the produced maps, reflects both the spatially varying amounts of soil excess ice and mapped landcovers.