Ninth International Conference on Permafrost ... - IARC Research

Mapping the Permafrost in China Using Remotely Sensed Land SurfaceTemperature DataXin Li, Shuguo Wang, Rui Jin, Youhua RanCold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences Lanzhou 730000, ChinaWorld Data Center for Glaciology and Geocryology in Lanzhou, Lanzhou 730000, ChinaThe permafrost area in China is about 1.72 × 10 6 km 2 . Thearea of altitudinal/mountain permafrost is approximately1.36 × 10 6 km 2 (Li et al. 2008), which ranks first in the worldin terms of middle- and high-altitude permafrost area. Thepermafrost in China is very sensitive to climatic warming.Significant permafrost degradation has occurred and isoccurring in most permafrost regions in China, and hasresulted in an increase of environment fragility and relatedhazards (Li et al. 2008, Jin et al. 2000, Jin et al. 2006).Mapping the permafrost is of critical importance therefore.The existing small-scale permafrost/frozen soil maps inChina include the map of snow, ice, and frozen ground inChina (1:4,000,000) (Shi et al. 1988), permafrost map of theQinghai-Tibet Plateau (1:3,000,000) (Li & Cheng 1996),the map of geocryological regionalization and classificationin China (1:10,000,000) (Qiu et al. 2000), and the map ofglaciers, frozen ground, and deserts in China (1:4,000,000)(Wang et al. 2006). In additional, the circum-Arctic mapof permafrost and ground-ice conditions (1:10,000,000)(Brown 1998) can be subset to be used as a regional map.These maps provide a good summary of geocryologicalresearch in China; however, there are two weaknessesof these existing small-scale permafrost maps. The firstis that the classification systems of these existing mapsare inconsistent. All of the legends are continuity-based,but each map uses a different and incomparable maplegend itself. The inconsistence is caused, partially, by theambiguity of the definition of continuity, which is based onthe surrounding region it is lying in and, therefore, is scaledependent(Nelson & Outcalt 1987). Obviously, a consistentand unified legend system is needed for both altitudinaland latitudinal permafrost mapping in China. The lack of ithinders the monitoring and modeling of permafrost.Another weakness of traditional permafrost mapping is thedata unavailability. Global and regional permafrost mappingusually relies on meteorological data. That most commonlyused is air temperature, but it is sparse in many permafrostareas, e.g., the Qinghai-Tibetan Plateau. The scarcity of datais an obstacle of high-resolution permafrost mapping.To address the first weakness, we propose using a stabilitybasedclassification system proposed by Cheng (Cheng 1984)to unify the legends of altitudinal and latitudinal permafrostmaps. This classification uses temperature criteria, which ismore objective than the continuity criteria. It is also moreapplicable when using GIS mapping technology, becauseGIS mapping is usually grid-based, which is easy forpresenting the existence of permafrost in a grid cell, but notthe percentage of permafrost distribution.To address the second weakness, we propose to use remotesensing data. As stated above, air temperature isotherm isusually used to delineate permafrost zonation. However,many investigators suggested that the air temperature isnot an optimal predictor of permafrost distribution, becausethe very large effects of snow cover and other variablesinfluencing permafrost occurrence are ignored. Instead,land surface skin temperature (LST) should be used (Nelson& Outcalt 1987, Cheng, pers. com.). The LST, though amore ideal criterion, is traditionally more unavailable thanair temperature and its heterogeneity is very strong so thatextracting LST to data-void regions is more difficult. Theremote sensing era has changed this situation. Thermalinfrared remote sensing is providing direct observations ofLST in high spatial and temporal resolutions, being capableof bridging the gap between permafrost mapping and dataunavailability.The paper aims to develop a new, general, and highresolutionpermafrost map of China by applying the thermalstability-based classification system (Cheng 1984) and usingremotely sensed LST and snow depth data.ReferencesCheng, G.-D. 1984. Problems of zonation of high-altitudepermafrost. ACTA Geographica Sinica 39(2): 185-193.Jin, H.J., Li, S.X., Cheng, G.D., Wang, S.L. & Li, X. 2000.Permafrost and climatic change in China. Global andPlanetary Change 26(4): 387-404.Jin, H.J., Zhao, L., Wang, S.L. & Jin, R. 2006. Thermalregimes and degradation modes of permafrost alongthe Qinghai-Tibet Highway. Science in China D:Earth Sciences 49(11): 1170-1183.Li, S.D. & Cheng, G.D. 1996. Permafrost DistributionMap on the Qinghai-Tibet Plateau. Lanzhou: GansuCulture Press.Li, X., Cheng, G.D., Jin, H.J., Kang, E.S., Che, T.,Jin, R., Wu, L.Z., Nan, Z.T., Wang, J. & Shen,Y.P. 2008. Cryospheric change in China.Global and Planetary Change, doi:10.1016/j.gloplacha.2008.02.001.Nelson, F.E. & Outcalt, S.I. 1987. A computational methodfor prediction and regionalization of permafrost.Arctic and Alpine Research 19(3): 279-288.Qiu, G.-Q., Zhou, Y.-W., Guo, D.-X. & Wang, Y.-X. 2000.The Map of Geocryological Regionalization andClassification in China. Beijing: Science Press.181