Ninth International Conference on Permafrost ... - IARC Research

Dynamics of the Cryosphere of Northern Tien Shan as a Reaction toClimate ChangeIgor V. SeverskiyKazakh Institute of Geography,Eduard V. SeverskiyPermafrost Institute of Russian, Academy of Sciences.On the basis of analysis of long-term observation, datachanges of snowiness, glaciation, and thermal regime ofseasonally and perennially frozen grounds in the mountainsof southeast Kazakhstan (Northern Tien Shan, DzhungharAlatau) for last decades are considered.According to analysis in the testified region, for the lastdecades the average maximum snow water equivalent (themain component of snow resources) has not changed. Similarresults were found for western Tien Shan and Gissar-Alai.Glacial systems of Central Asia mountains develop in thesame direction and have similar rates of modern changes; sofor the last decades, the area of glaciers in different regionsof Tien Shan, Gissar-Alai, Pamirs and Dzhunghar Alatau hasdecreased at the average rate 0.8–1.0% per year.The dimensions and temperatures of the glacier degradationhave been determined on the basis of comparison of dataof the unified Glacier Inventories, composed by aerophotographmaterials and by satellite images for 6 yearswithin the period of 1955 to 1999.Mean maximum glacial retreat rates at the Northern TienShan characteristic of the mid-1970s by the mid-1980sslowed down.Glacier retreat rate depends to a great extent on its size.A glacier area F = 13–14 km 2 is the threshold. In case ofits excess, the self-regulation mechanism of the glacier is sovivid that it neutralizes evidence of all local factors, and itsregime is defined by microclimatic conditions of the region.The regime of each glacier is unique and can differ fromnot only average data for this type of glacier system, but alsofrom that of a nearby glacier. The differences can be not onlysignificant but also can have a different negative/positivetrend. Glacier retreat rate does not depend on its expositionand morphological type. Territorial differences in the retreatrates are defined by the orientation of slopes in reference tothe sides of the horizon and the prevailing direction of humidair mass movements, and the location of the region in themountainous system.Predominating opinion about the inevitability of glaciersdisappearance in Central Asia mountains cannot be acceptedas an axiom. Taking into account stability in the rate ofprecipitation and especially in the rate of snow resources,one can suppose that glaciers in this region will not disappearduring this century. Based on our analysis, which takes intoaccount current global warming trends, the glacier area ofBalkhash Basin may shrink by about one-third, but will notdisappear completely.Most scientific publications support an opinion thatthe glacier runoff must increase with glacier retreat dueto global warming. Our research shows that the result ofmodern climate warming is glacier runoff decrease. Butdespite the reduction of glaciers, annual runoff volumesand the interannual distribution remained unchangedduring the last decades. During the same period, normsof atmospheric precipitation and maximum snow waterequivalent in the zone of runoff formation remained stablealso. All these allow the proposal of the existence of acertain compensation mechanism. Research, based on dataanalysis of repeated photogrammetric surveys of a group ofglaciers and temperature regime of permafrost in ZailiyskiyAlatau, suggests that such mechanism can be an increased(with climate warming) participation of melting waters ofground ice (buried glaciers, rock glaciers, permafrost) in theriver runoff.Taking into consideration, also, the fact that reserves ofground ice in high mountains of Central Asia and Kazakhstanare equivalent to present-day glacier resources and in theChinese mountains they are two times greater, and alsoconsidering that the rates of melting ground ice are muchlower than those of the open glaciers, we believe that evenif the present-day trends in climate warming are preserved,the above-mentioned compensating mechanism may workduring several coming decades as minimum. Hence it canbe predicted that the ongoing degradation of glaciers willnot cause considerable reduction in the runoff and regionalwater resources, at least up to the next decades.Materials from 33 years of geothermal monitoringtestify to the ambiguous reaction of perennial and seasonalpermafrost to climate changes in the Northern Tien Shan.Regularities of perennially frozen ground distribution andfeatures of spatial changes of depth and character of seasonalfreezing of soils in the Northern Tien Shan are reflected inthe regional structure of altitudinal geocryological zonalityThe total area of perennial permafrost tracts in the subzonewith sporadic spreading amounts to not more than 1–2%, itcomes up to 30% at insular spreading, it rises up to 70% atintermittent distribution, and at dense one, it is not less than90% of the total subzone area. There are not any conditionsfor formation of local masses of permafrost on a southernmacro-slope; therefore the subzone of sporadic spreading isabsent there. Altitude borders of other subzones are locatedthere on 300–400 m above in comparison with the positionon a northern slope.During the period of 1974–1995, ground temperature inlayer of perennial permafrost had increased 0.2–0.5°С, butafter that, has been retained at -0.2°С during the last 11years.281