全球变化知识资源中心

The increase in low flows (winter discharge and minimum monthly discharge), caused primarily by permafrost degradation, is common in high-latitude permafrost regions, whereas the dynamics of low flows in high-altitude permafrost regions remain largely unknown. Long-term discharge data from 28 unregulated catchments in western China were analysed, and the findings showed that winter discharge/minimum monthly discharge significantly increased (p <= 0.1) in 82/82%, 55/64%, and 0/0% of the catchments in the higher-latitude mountain permafrost regions (Tienshan Mountains), mid-latitude mountain permafrost regions (Qilian Mountains), and mid- to low-latitude plateau permafrost regions (the source regions of the Yangtze and Yellow rivers), respectively. The differences in permafrost type and the distribution of permafrost and alpine cold desert (which is similar to tundra) were found to be the main causes for the different responses in the low flows. The rate of change of low flows (winter discharge and minimum monthly discharge) was negatively and linearly correlated with permafrost coverage when coverage was less than 40% of the catchment area, whereas the low flows changed only slightly when the permafrost coverage exceeded 40%. A significant thickening of the active layer increased the low flows in the lower permafrost-covered catchments, which are dominated by warm permafrost. However, in the higher permafrost-covered catchments with cold permafrost and a cold climate, only an increase in permafrost temperature (without a notable thickening of the active layer) occurred, resulting in non-significant changes in low flows.