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 1960 s,the extent of Xing’an permafrost in Northeast China had decreased by 40.6% by the 2010 s.With an average rate of increase in mean annual air temperatures at 0.03℃ a-1,the extent of permafrost in Northeast China will decrease to 26.42× 10~4 by 2020,14.69 × 10~4 by 2040 and to 11.24 × 10~4 km~2 by2050.According to the ground-surface temperature frostnumber criteria,the southern limit of latitudinal permafrost was at the 0.463.From the 1960 s to the 2010 s,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.