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Section 3. Geography
Rakhmonov Komiljon Radjabovich, Khikmatov Fazliddin Khikmatovich, Prof. Dr., National University of Uzbekistan named after Mirzo Ulugbek, Lecturer of the Faculty of geology and geography, Tashkent city, Uzbekistan E-mail: [email protected]
FORECAST OF WASH INTENSITY FROM HIGH MOUNTAIN RIVER BASINS OF CENTRAL ASIA WITH THE CHANGE OF CLIMATE
Abstract: The paper considers the problems of forecasting the wash intensity of soils from the surface of the high-mountain river basins in Central Asia, taking into account climate change.
Keywords: river, high-mountain basin, glaciation, soil erosion, suspended sediment flow, climate change, climate scenarios, statistical evaluation, nomogram, forecast, washout intensity.
phological model by Shcheglova [8], to characterize the temperature regime, the average height of the lower boundary of the glaciers was chosen. At the same time, the entire glaciation area of the river basin is taken into
Introduction
Currently, the largest reservoirs of the Central Asia are Toktagul, which was built on the course of Naryn river, with a volume of 19,5 km 3 and Nurek — on the course ofVahsh river, with a volume of 10,5 km 3 etc. The main tasks of these reservoirs are the long-term regulation of the river flows of fed from the highmountain regions of Central Asia. Effective use of these expensive hydraulic structures, together with whole water and energy resources of the high-mountain part of Central Asia requires an assessment of the erosion of fine soil by rivers whose basins bear the modern mountain glaciation.
The main aim of this research is to improve the methodology of predicting soil washout intensity from the surface of high-mountain basins in river Central Asia under the climate change.
Data. The runoff of suspended sediments of the studying rivers, the air temperature taken into account at representative high altitude stations and the total area of glaciation of the basins were used as the main source materials.
Methods of research. In the study of prognostic dependence, the objective method of equalization and normalization of correlation relationships, proposed by Alekseyev [1], was applied. Different from climatomor-
account. Recommendations of A. S. Shchetinnikov, A. N. Krenske and others [7] were used on calculating the average summer temperature at the level of the average height of the lower boundary of glaciers.
Results and discussion. As a result of special -estimation withusing objective method of equalization and normalization of correlation relationships the equation of normalized regression obtained the following form: Uo(Mr) = °.651 . Ui(Fj + °.453 . U^l Where U° (Mr1, U1 (Fgla) ^J - are the normalized values, of the flush module, the total glacier area and the mean temperature at the average elevation of the lower boundary of the glaciers, respectively.
The tightness of the connection of this equation is characterized by a total correlation coefficient of 0,761 ± ± 0,035. On the basis of this equation, a nomogram for calculating the soil washout module (MR) was constructed from the catchments of the snow-glacial fed and glacial-snow fed types according to the classification of Shchulz (Fig. 1).
Figurel. Nomogram for calculating the flushing module (MR) from the catchments of the snow-glacier fed and glacier-snow types fed in the glacier basin area (lgFglac) and the mean air temperature for June-September (f/V_IX) at the mean height of the glacier ends
The constructed nomogram allows estimating the soil washout module from the surface of the basins of the studied rivers by their glacier area (lgFglac) and average air temperature for June-September (ijV-IX) at the average altitude of the ends of mountain glaciers.
It is known, currently the several models exist, e. g. global climate change scenarios recognized by the World Meteorological Organization (WMO): the MGFDL -
Model of the Geophysical Fluid Dynamics Laboratory (USA), the MGISS - model of the Goddard Institute for Space Sciences (USA); the MUKMO - Model of the U. K. Meteorological Office, and the CCCM - model of the Canadian Climate Center. In the work we used these models in the interpretation of the scientists of Hydro-meteorological Research Institute (NIGMI) of Uzhy-dromet, for the conditions of Central Asia (Table 1).
Table 1. - Changes in air temperature and precipitation according to models of global climate change
Climate model Air temperature, ° C Atmospheric precipitation, in%
CCCM + 6.5 -11
UKMO + 5.2 + 6
GFDL + 3.4 + 14
GISS + 4.7 + 13
Note: (+) - increase in temperature or increase in precipitation; (-) - decrease.
In this research, the flushing intensity was estimated taking into account only the climatic changes, since the flow formation zone is mainly located in mountainous areas and does not have a strong influence of non-climatic changes as anthropogenic factors.
Estimation of the change in the runoff modulus of high-mountain rivers, due to changes in air temperature, according to different climatic scenarios is based on the nomogram (Fig. 1.)
Obtained results in (Table 2) indicate that the largest changes in the sediment runoffmodule are observed in the first climate scenario (CCCM). According to this model, increasing temperature at the lower boundary of the glaciers by a factor of 2.7 leads to an increase in the flushing modulus by 3.2 times. Relatively small flushing changes correspond to the third climatic scenario (GFDL), where as a result of a temperature increase of 1.9 times, the flow modulus increases by 2.1 times (Table 2).
Table 2. - Module for sediment discharge of the snow-glacial fed and glacier fed river types due to changes in air temperature according to different climate scenario
Hydroclimatic characteristics Climate scenarios
CCCM UKMO GFDL GISS
Average temperature at the lower boundary of glaciers, tH, °C 3.8
Temperature increase, °C 10.3 9.0 7.2 8.5
Relative temperature rise tH 2.7 2.4 1.9 2.2
Average sediment discharge module, MR, ton/km 2 634
Change of sediment discharge module, MR, ton/km 2 2055 1764 1362 1624
Increase in relative sediment discharge module MR 3.2 2.8 2.1 2.6
In addition, it should be noted that a long-term change in air temperature affects the glaciomorphologi-cal parameters of mountain glaciers, especially their area. In estimating the change in the sediment runoff module, the decrease in glacier area of tion is also taken into account. The decrease in the area of glaciation by an average of 12.5% (A. S. Shetinnikov, 1997, 1998) does not lead to sharp decreases in the sediment flow rate ofhigh-mountain rivers. In percentage terms, they vary within 7.6-9.2%.
Changes of state of glaciers and their parameters are also determined by the amount of precipitation. Therefore, while assessing changes in flushing from the highmountain zone, it is necessary to take into account not only the changes in air temperature and atmospheric precipitation, but also the subsequent evolution of mountain glacier systems.
Conclusions. An assessment was made of the change in the intensity of the washout of soil from the catchments of the high-mountainous Central Asian region in connection with the expected climate change. Calculations performed according to different climatic scenarios showed the following: according to the climate scenario of the CCCM, the sediment runoff module increased average by 3,2 times with an increase in temperature of 2.7 times, and according to the GFDL model, as a result of an increase in temperature of 1,9 times, the modulus of flow increases 2.1 times. In general, when assessing changes in flushing from the high-mountain zone, it is necessary to take into account not only the changes in air and precipitation temperature, but also the degradation accompanying them, and evolution in the future (G. E. Glazyrin, 1985, 1991; A. S. Shetinnikov, 1997, 1998) of mountain glacier systems.
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