"Glaciers and climatic changes "
Source: Interstate Commission for Water Coordination of Central Asia / Assessment of water resources changes under probable climatic change / http://dialogue.icwc-aral.uz/index/third/agaltseva/05_chapt5.pdf
Glaciers and climatic changes
Presently, glaciers shrinking are under consideration. What is the cause: green house effect or climatic cycles? According to V.M. Kotlyakov, during last 420 thousand years there were 4 climatic cycles.Cold periods were longer than warm ones. Because of different causes temperature sharply reduced and fell with difference up to 10Сo. Even during last millennium temperature fluctuations amounted for 1.5-1.0 Сo. YII, XVI, XX centuries were warm as well as XIII-XY and XYII-XIX centuries were cold. Present warming does not come beyond natural fluctuations in spite of higher green house concentration . Glaciers located in the mountains are main source and long-term reserve of fresh water. But ice stock is not stable. Presently, glaciers retirement is observed: small glaciers disappear and large ones are being broken. Glacier shrinking leads to snow melt flow reduction. Observations in various glacier regions showed that flow reduces slower than glacier area. Actual area of glacier grows due to its separation. Different researches note incompliance between snow melt increase and glacier area reduction. Scientists have found that .long-term flow changes linked with glaciers degradation are shadowed by snow melt increase in dry years: glacier area decreases and flow increases..
Glaciers differently response to air temperature increase. Calculations performed for summer temperature change by 0.5Сo and 1Сo and annual precipitation by 20% showed that temperature change by 1Сo leads to change of firn ice border change on 120.140 m.
The same effect gives precipitation reduction by 20%. These characteristics effect on glacier area is more complicated. Maybe it depends on precipitation distribution and relief structure. These factors change much for various basins and lead to different results. For instance, temperature increase by 0.5Сo leads to glacier area in Sokh and Isfara basin reduction by 8%, in Margilandaya, Kashkadarya and Oihangs basin by 30%. Temperature
increase by 1Сo reduces glacier area twice. It worth to remind that long-term temperature change influence is difficult to find. If to consider glacier evolution during last 50 years and compare data on glacier morphometry in USSR Catalogue (1965-1982) with ground observations and aerospace images, some glaciers show stationary state and even increase (liner size increase, .dead tongue. animation). For main mass of glaciers signs of reduction are typical: glaciers with area less than 1 km2 disappear, large glaciers are broken into small ones, morena area glacier and pollution increase. Glacier response to climatic parameters (temperature, precipitation) changes has inert character: lag depends on area (0-10 years). It is necessary to note following peculiarities of glacier flow: Firstly, its share depends on snow amount during preceding winter and winter ablation. In low snow years glaciers are spent for flow compensating lack of snow melt and rain. Secondly, glacier flow reaches maximum in July-August when other water sources (seasonal snow and rain) are exhausted. If big glaciers are located in flow formation zone and glacier recharge exceeds 5-10% of total annual inflow, calculation without regard for glacier flow leads to big discrepancies in mountainous river flow modeling. For that model of glacier flow formation is included in a set of models because it computers total flow from glaciers including snow melt, ice and firn. For description and calculation of total melt water all glaciers within region under consideration are considered as single ice area. Dependant of basin size within this area several rayons are excreted uniting multitude of similar glaciers. Mathematical and physicalstatistical models of snow and ice accumulation and melting within annual cycle are taken as a methodological base.
It is evident that river basin frozenness depends on relief and climatic conditions. It is known that for high mountains firn line is integral climatic indicator. Accuracy of frozenness assessment is determined by climatic scenarios reliability. Frozenness response to climatic changes assessment was performed for Ghissar-Alai based on methodology described in . Since in all scenarios temperature increase is assumed, all combinations of temperature (0, 1, 2, 3Сo.) and precipitation (.50%, 0%, 50%,100%) changes were taken. Results showed that option is optimal when temperature is unchanged and precipitation is doubled. In this case firn line height reduces by 0.5km that will lead to sharp increase of glacier area and flow.
Option is the most unfavorable when precipitation decreases twice and temperature increasesby 3Co: firn line goes up by 700 m, frozenness area reduces by 86%, glacier flow by 96%. Obtained results show that climatic conditions change under temperature increase by
1-2°С will lead to river flow reduction of both types of recharge. Temperature increase by 1-2°С will foster glacier degradation process. For 1957-1980
glaciers within the Aral Sea basin lost 115.5 km3 of ice (near 104 km3 of water) that constitutes almost 20% of ice stock by 1957. By 2000 losses amounted for 14% of 1957 stock. By 2020-2025 glaciers will loose 10% more from initial volume.
Calculations of glacier flow done under .transition. scenarios (ICHAM, HADSM) showed that under those scenarios glacier flow reduction (3-5%) will occur by 2025 because under frozenness area reduction melting will occur at expense of melting layer increase.