Mountain permafrost distribution modeling using Multivariate Adaptive Regression Spline (MARS) in the Wenquan area over the Qinghai-Tibet Plateau

In high mountainous areas, the development and distribution of alpine permafrost is greatly affected by macro- and mi- cro-topographic factors. The effects of latitude, altitude, slope, and aspect on the distribution of permafrost were studied to under- stand the dislribution patterns of permafrost in Wenquan on the Qinghai-Tibet Plateau. Cluster and correlation analysis were per- formed based on 30 m Global Digital Elevation Model （GDEM） data and field data obtained using geophysical exploration and borehole drilling methods. A Multivariate Adaptive Regression Spline model （MARS） was developed to simulate permafrost spa- tial distribution over the studied area. A validation was followed by comparing to 201 geophysical exploration sites, as well as by comparing to two other models, i.e., a binary logistic regression model and the Mean Annual Ground Temperature model （IVlAGT）. The MARS model provides a better simulation than the other two models. Besides the control effect of elevation on permafrost distribution, the MARS model also takes into account the impact of direct solar radiation on permafrost distribution.

Lakes in the Qinghai-Tibet Plateau are conducive to regional permafrost development

The Qinghai-Tibet Plateau(QTP)possesses the largest areas of permafrost in the midand low latitude regions on the earth and many large lakes in the permafrost area.Based on a comprehensive investigation around certain typical lakes,this study found that although the presence of lakes formed different ranges of unfrozen zones in permafrost,the heating effect of lake water on surrounding permafrost is limited to a small extent.The temperature of permafrost around the lake is closely related to the distance to the lake and the ice content of the permafrost.Around lakes are ice-rich permafrost zones and permafrost temperature in this area is significantly lower than that far away from the lake,which indicates that the existence of lakes in the QTP has special effect on the permafrost distribution.Based on the monitoring results,this study presents the typical distribution pattern of the permafrost around large lakes and discusses the reasons for the distribution pattern.Due to the huge area of lakes and the significant impact of lakes on permafrost distribution,it is suggested to re-estimate the total permafrost area and underground ice storage in the QTP.

Dynamics of freezing/thawing indices and frozen ground from 1900 to 2017 in the upper Brahmaputra River Basin, Tibetan Plateau

Dynamics of the frozen ground are key to understand the changes of eco-environment in cold regions,especially for areas with limited field observations.In this study,we analyzed the spatial and temporal variations of the ground surface freezing and thawing indices from 1900 to 2017 for the upper Brahmaputra River(also called the Yarlung Zangbo River in China)Basin(UBRB),southwestern Tibetan Plateau,with the air freezing and thawing indices using the University of Delaware(UDEL)monthly gridded air temperature dataset.The abrupt change years for air freezing index(AH)and ground surface freezing index(GH)were detected in 1999 and 2002,respectively,and for both air thawing index(ATI)and ground surface thawing index(GTI)were 2009.With the air temperature rising at a rate of 0.006℃ per year over 1900-2017,the AH and GH decreased at a rate of-0.1℃ d per year,while the ATI and GTI increased at rates of 0.3 and 0.5℃ d per year before the abrupt change year,respectively;all changing trends of freezing/thawing indices increased after the abrupt year,which was-2.9,-0.8,7.3,and 21.7℃ d per year for the AH,GFI,ATI,and GTI,respectively.We utilized the surface frost number model to obtain the dynamics of the frozen ground over the UBRB.When the empirical coefficient of E was assigned to 1.2,the simulated frozen ground occupied about 53.2%of the whole UBRB in the 1990s,which agreed well with the existing permafrost map published in 1996.The area of frozen ground accounts for 51.5%-54.5%of the UBRB during 1900-2017.This result may facilitate further studies of the multi-interactions among the frozen ground and relevant eco-environment,such as the air-ground surface energy exchange,hydrological cycles,and changes of the active layer thickness over the UBRB.