| Permafrost,defined as ground that remains below 0°C for at least two consecutive years,is a product of cold climates.Permafrost is considered as one of the major components of the cryosphere due to its wide extent and strong influence on the environment,such as surface energy balance,hydrological processes,biogeochemical processes,and engineering activities.To investigate the thermal characteristics and dynamics of permafrost as well as seasonally frozen ground over the upper reaches of the Heihe River Basin(URHR),an observation network with fourteen boreholes was established during 2011–2014.The in-situ measurements indicated mean annual air temperature ranged from-2.4°C to-5.2°C at the monitored elevation range of about 3600–4150 m,and mean annual ground surface temperature ranged from-1.3°C to 1.7°C during 2013–2017.The mean annual ground temperature at 16–18 m depth ranged from-1.8°C on the high(>4000 m a.s.l)north-facing slope to near zero around areas near the lower limit of permafrost.Active layer thickness at the monitored sites varied significantly with the range of 0.77–4.84 m during 2011–2017,and maximum frozen depth in seasonally frozen ground was around 5 m.Permafrost thickness was between~136 m and less than 10 m.Both permafrost and seasonally frozen ground were found to be subject to serious warming during the measured period in the URHR.This study provides new quantitative insights for permafrost and seasonally frozen ground in the URHR.The active layer plays a key role in geomorphic,hydrologic,and biogeochemical processes in permafrost regions.We conducted a systematic investigation of active layer thickness(ALT)in northeastern Qinghai-Tibetan Plateau by using ground-penetrating radar(GPR)with 100 and200 MHz antennas.We used mechanical probing,pit,and soil temperature profiles for evaluating ALT derived from GPR.The results showed that GPR is competent for detecting ALT,and the error was±0.08 m at common midpoint co-located sites.Considerable spatial variability of ALT owing to variation in elevation,peat thickness,and slope aspect was found.The mean ALT was 1.32±0.29m with a range from 0.81 to 2.1 m in Eboling Mountain.In Yeniu Gou,mean ALT was 2.72±0.88m and varied from 1.07 m on the north-facing slope to 4.86 m around the area near the lower boundary of permafrost.ALT in peat decreased with increasing elevation at rates of-1.31m/km(Eboling Mountain)and-2.1m/km(Yeniu Gou),and in mineral soil in Yeniu Gou,the rate changed to-4.18 m/km.At the same elevation,ALT on the south-facing slope was about 0.8 m thicker than that on the north-facing slopes,while the difference was only 0.18 m in peat-covered area.Within a 100 m~2 area with a local elevation difference of 0.8 m,ALT varied from 0.68 m to1.25 m.Both field monitoring and modeling studies on spatial ALT variations require rethinking of the current strategy and comprehensive design.Compiling permafrost distribution over the URHR is expected to be challenging largely due to limited data sets and strong spatial heterogeneity.Benefit from recent economical,engineering,and scientific activities,a large number of permafrost investigations(e.g.,borehole drilling,soil pit,soil temperature profile,and geophysics)have been conducted over the area.Here the first time,we present the inventory of permafrost presence/absence with 523 sites/plots over the UHHR.Based on the in-situ measurements,a new high-resolution(30 arcsec)permafrost zonation index(PZI)map was generated by using multi-variable of air temperature and snow water equivalent based on generalized linear model.Our results showed the permafrost distribution model,and hence PZI map,was robust established with overall classification accuracy of 84.5%.Excluding glaciers and lakes,the permafrost region and area were established as about 15.4×10~3 km~2 and 12.5×10~3 km~2,respectively. |
PDF Full Text Request