Evaluation of the effect of meteorological factors in the flow of the Chirchik basin rivers

The flow of rivers varies not only throughout the year, but also varies from year to year. Many years of water quantities are mainly related to cirrhosis of air masses in the atmosphere, which is exposed to many years of climate. Atmospheric precipitation in almost years, the amount of water increases or can be the opposite. In addition, the perennial vibration of the amount of water depends on geological, tectonic processes. At the same time, the air temperature is of great importance in the rivers for glaciate waters. [3, 4]. Considering these cases, the study of the impact of climatic factors for the flow of rivers, which is reduced to a reservoir is one of the current issues of today.

Rivers of Chirchik Basin were selected as an object of research facilities. The quantitative assessment of meteorological factors in the flow of rivers will determine the study of the work.

The main purpose of this work is to quantify the impact of meteorological factors on the flow of rivers in the Chirchik basin. The following tasks have been identified in achieving the goal set in the research work:

• -    Coverage of the natural conditions and hydrometeorological study of the area where the Chirchik basin is located;

• -    Study of distribution of rivers flow throughout the year;

• -    Assessment of annual fluctuations of river flow and the impact of meteorological factors on it;

• -    Statistical assessment of river flow variability.

The scientific novelty is displayed in the following:

• -    The hydrometeorological study of the rivers of the Chirchik basin was covered from the point of view of the subject;

• -    the annual and inter-annual variation of river flow was studied;

• -    the multidimensional relationships between river flow and meteorological factors were statistically assessed;

• -    the variability of river flow was statistically assessed.

The scientific significance of the results of the study is that they can be used as an important scientific resource in the rational use and protection of river water resources, as well as in the development of action plans for the efficient use of water resources in the study area. The practical significance of the work is determined by the fact that the main conclusions and recommendations made on the basis of the results of the work, the information collected in it, serve to improve the quality of the educational process in the relevant areas of education and specialties.

The first studies on the influence of meteorological factors, including atmospheric precipitation and air temperature, on the formation of rivers in Uzbekistan, including the Chirchik Basin, were conducted in the early twentieth century. Issues of formation of mountain river flow and study of natural geographical factors determining it have been studied by V.G. Glushkov, E.M. Oldekop, L.K. Davidov, N.L. Korjenevskiy, V.L. Shults, O.P. Sheglova, A.N. Vajnov, M.N. Bolshakov, A.M. Vladimirov, I.S.Sosedov, F.H.Hikmatov and others. The distribution of annual runoff can be calculated for any period of time in rivers based on water consumption monitoring data. Therefore, in the study, the monthly distribution of the Piskom River (Mullala village) flow throughout the year was studied for multi-aquatic (1969), average perennial (1965-2018), and low-aquatic (1982) years.

According to the results of calculations, the estimated costs for extremely high-water years increase in hot summer periods. The main reason for this is related to the sources of saturation of the river. This is because the constant snow and glaciers in the high mountains begin to melt under the influence of summer temperatures, and the water in the river increases during these months [2].

Based on the results of calculations of the distribution of the flow of the river Piskom on a monthly basis during the year, diagrams of the monthly distribution of the flow during the year were drawn (Figure 1).

It can be seen from this diagram that in a multi-aquatic year (1969) the flow of the Piskom River is unevenly distributed throughout the year. For example, while January accounted for 4.11 % (79.6 million m3) of the flow, by February, these values had declined slightly (3.49 % or 68.5 million m3). Since March, the water level in the river has increased to 140.4 million m3. This is 7.26 % of the annual flow. The river had relatively high water levels in May, June, July and August. While the flow in July was 989 million m3 (52%), the amount of water in the river has been declining since September (795 million m3). The flow rates in the river, determined on the basis of low water and average perennial values, are also unevenly distributed over months (Figure 1).

Annual changes in river flow occur as a result of meteorological factors (atmospheric precipitation, air temperature, humidity). The fact that the annual rainfall in rivers saturated with rain and snow is higher than the norm also leads to an increase in river flow. In rivers saturated with constant snow and glacial water, summer temperatures are higher than normal, which leads to an increase in river flow. In both cases, other factors affecting river flow remain secondary [1, 3, 4].

W, %      Average perennial (1965-2018 yy.)

Figure 1. Distribution of the Piskom River flow by months during the year

Based on the above, diagrams of meteorological factors, in particular atmospheric precipitation and air temperature change, with the flow of the Piskom and Chatkal rivers were drawn (Figure 2 and 3). It can be seen that the influence of atmospheric precipitation on the formation of the Piskom River flow is much greater Changes in atmospheric precipitation with the flow of the Piskom River are often mutually exclusive. In the diagram drawn for river temperatures and air temperatures, however, such compatibility is not observed in some years.

To increase the accuracy of the relationship between river flow and meteorological factors, it is necessary to take into account air temperatures along with atmospheric precipitation. In this case, the multidimensional relationship between river flow and meteorological factors is statistically assessed [1, 3].

А)

Х, mm

—Х -*-Q

Q, m3/sec

1960    1970    1980    1990    2000    2010    2020 Т, years

B)

X, mm

XQ

Q, m3/sec

1960    1970    1980    1990    2000    2010    2020 Т, years

Figure 2. Annual variation of atmospheric precipitation recorded at the Piskom meteorological station with the flow of the Piskom (A) and Chatkal (B) rivers.

Table 1. Air temperature and precipitation trends recorded on the Piskom and Chatkal rivers and at the Piskom meteorological station

Piskom (Mullala v.)	Chatkal (Hudoydodsoy v.)	Piskom MS
Trend equations
Q = -0,224x + 522,8	Q = 0,655x - 1191,5	Х = 1,874x - 2858 t = 0,017 - 24,04

The analysis of the graphs shows that the effect of atmospheric precipitation on the formation of the studied river flow is noticeable. Changes in atmospheric precipitation with the flow of the Piskom and Chatkal rivers are often mutually exclusive. In the graph drawn for air temperatures with river flow, however, such compatibility is not observed in some years. Given all the above considerations, it is necessary to take into account air temperatures along with atmospheric precipitation to increase the accuracy of the relationship between river flow and meteorological factors. In this case, the multidimensional relationship between river flow and meteorological factors is statistically assessed.

Based on the results obtained in the study, the following conclusions were made:

• 1.    The month-to-month distribution of the Piskom River flow over the year was studied for multi-aquatic (1969), low-water (1982), and average perennial (1965-2018) values. At perennial averages, river flow is unevenly distributed over months. In January, 61.9 million m³ of annual flow, or 2.6 percent, flowed, while in February it decreased slightly (2.2%). Starting in May (367 million m³), the flow in the river increased and continued until July (280 million m3 or 11.6 percent);

• 2.    The maximum value of the average monthly water consumption observed in the Chatkal River is Q = 314 m³/sec, which corresponds to July. The value of the flow volume in July was W VI = 813 · 106 m³, which is 22.6 per cent of the annual flow. According to the calculations, the flow volume in February amounted to only 2.4% of the annual flow rate.

• 3.    Graphs of the combined changes in meteorological factors, in particular atmospheric precipitation and air temperature, with the flow of rivers were drawn. These graphs used data on average annual water consumption observed at the Mullala and Hudoydodsoy hydrological posts of the Piskom River and the annual atmospheric precipitation and average annual air temperatures recorded at the Piskom meteorological station.