Climate warming over 1961–2019 and impacts on permafrost zonation in Northeast China

In boreal forest ecosystems, permafrost and forest types are mutually interdependent; permafrost degradation impacts forest ecosystem structure and functions. The Xing’an permafrost in Northeast China is on the southern margin of the Eastern Asia latitudinal permafrost body. Under a warming climate, permafrost undergoes rapid and extensive degradation. In this study, the frost-number (Fn) model based on air temperatures and ground surface temperatures was used to predict the distribution of the Xing’an permafrost, and, temporal and spatial changes in air and ground-surface temperatures from 1961 to 2019 are analyzed. The results show that Northeast China has experienced a rapid and substantial climate warming over the past 60 years. The rises in mean annual air and mean annual ground-surface temperatures were higher in permafrost zones than those in the seasonal frost zone. The frost numbers of air and ground-surface temperatures were calculated for determining the southern limit of latitudinal permafrost and for permafrost zonation. The southern limits of discontinuous permafrost, sporadic permafrost, and latitudinal permafrost moved northward significantly. According to the air-temperature frost-number criteria for permafrost zoning, compared with that in the 1960s, the extent of Xing’an permafrost in Northeast China had decreased by 40.6% by the 2010s. With an average rate of increase in mean annual air temperatures at 0.03 °C a−1, the extent of permafrost in Northeast China will decrease to 26.42 × 104 by 2020, 14.69 × 104 by 2040 and to 11.24 × 104 km2 by 2050. According to the ground-surface temperature frost-number criteria, the southern limit of latitudinal permafrost was at the 0.463. From the 1960s to the 2010s, the extent of latitudinal permafrost declined significantly. Due to the nature of the ecosystem-protected Xing’an-Baikal permafrost, management and protection (e.g., more prudent and effective forest fire management and proper logging of forests) of the Xing’an permafrost eco-environment should be strengthened.