Psychological Adaptation Mediates the Climate Livability–Settlement Intention Link: A Case Study of In-Migrants in Harbin, China

High-latitude, cold-climate cities have long faced inherent climatic disadvantages due to prolonged frigid winters, historically limiting their attractiveness for population inflow. Global warming, particularly the polar amplification effect, offers potential for improving climate livability in such cities, creating new opportunities for population redistribution and urban development. Taking Harbin, a representative cold-climate city in Northeast China, as a case study, this research integrates meteorological data (2010–2023) with questionnaire responses from 1053 recent in-migrants. Using Analytic Hierarchy Process and Structural Equation Modeling, we systematically examine how climate livability is associated with migration decisions. The key findings are as follows. (1) Harbin’s climate livability improved significantly from 2010 to 2023. (2) In-migrants display a spatial pattern of “proximate dominance and distant diversity”, with pronounced heterogeneity in climate perception and satisfaction across origin regions. (3) Climate livability is associated with settlement intention through a partial mediation pathway: the indirect effect via deep adaptation (β = 0.330) accounts for 37.2% of the total effect, while a significant direct effect (β = 0.559) also exists, correcting an earlier inflated full-mediation estimate. (4) This perception–adaptation–decision pathway remains stable across subgroups and is not significantly moderated by origin climate contrast or occupational exposure, although boundary conditions apply. (5) Migration decisions involve trade-offs between climatic experience and socioeconomic rationality: climate livability reinforces long-term settlement intentions through psychological adaptation, while short-term migration is chiefly driven by socioeconomic factors. These findings provide empirical evidence and policy insights for cold-climate cities, such as Harbin, aiming to establish inclusive adaptation support systems and implement phased, context-sensitive population strategies.