Abstract
Aufeis is a seasonal ice accumulation formed by successive freezing of groundwater or surface-water overflow on land surfaces, river ice or lake ice during winter. It is widespread across cold regions and plays important roles in hydrology, geomorphology, ecosystems, and infrastructure stability, yet remains underrepresented in regional and global cryospheric assessments. This review synthesizes recent advances in aufeis research, focusing on spatiotemporal distribution, formation mechanisms, seasonal dynamics, environmental functions, engineering impacts, and mitigation strategies, while identifying major knowledge gaps and future research priorities. Current evidence suggests that aufeis extent has generally declined in many cold-region landscapes over recent decades, although large uncertainties persist in forested, mountainous, and data-sparse regions, particularly across Asia. Under continued climate warming and hydroclimatic intensification, aufeis is likely to become smaller, more fragmented, and less spatially continuous. However, its response is not uniformly negative: permafrost degradation may locally enhance groundwater recharge, talik development, and winter baseflow, thereby promoting aufeis formation in some settings. This dual response highlights the strong dependence of aufeis dynamics on local hydrogeological structure, permafrost conditions, snow regime, and surface–subsurface connectivity. Beyond its geomorphic expression, aufeis can function as an important seasonal water reservoir, contributing substantially to spring and early-summer runoff and, in some basins, rivaling or exceeding the hydrological contribution of nearby small glaciers. These hydrological functions are critical for sustaining cold-region ecosystems, regulating streamflow seasonality, and buffering water scarcity during early thaw periods. At the same time, aufeis poses persistent and in some cases growing risks to roads, railways, pipelines, and other linear infrastructure, prompting a shift from conventional passive control measures toward integrated, process-informed, resilience-based mitigation. Aufeis-related landforms, sedimentary records, and geochemical signatures also provide valuable archives for reconstructing Quaternary hydrogeological and periglacial environments. A process-based, interdisciplinary understanding of aufeis is therefore essential for predicting its response to climate change, improving cold-region water resource assessment, interpreting paleoenvironmental records, and supporting the design, maintenance, and adaptation of resilient infrastructure in a warming cryosphere.