Keywords

1 Introduction

The Naryn River is the largest water artery in Kyrgyzstan. In the outlet section (hydropost Uchkurgan), the area of the basin is 58400 km2, the annual discharge is estimated at 432 m3/s [1,2,3,4]. Its runoff used for hydropower and water management purposes. In the future, it planned to build 24 hydroelectric power stations in the Naryn river basin. At the same time, their construction in the upper reaches of the Naryn River was planned for the coming years. This determines the relevance of studying the water regime of the Naryn River.

The hydrological regime of the upper reaches of the Naryn River was described according to the data of a hydrological station located in the city of Naryn; climatic characteristics were determined according to long-term data of the Tien Shan meteorological station (3614 m above sea level) and Naryn (2040 m above sea level).

2 Relevance, Scientific Significance of the Issue

The problem of water supply for the population and various sectors of the economy has become relevant for many regions of the world. The uneven distribution of river flow within regions is becoming a serious problem, especially in arid regions of the world. These regions include the Central Asian region.

Kyrgyzstan has changed water relations with neighboring Republics. According to previous agreements, the use of water from the Toktogul reservoir, compared to energy, was focused on irrigation purposes. Energy is currently at the forefront.

This is due to the fact that Kyrgyzstan uses only 2% of the total volume of water from the Nizhne-Naryn HPP for irrigation. In addition, Toktogul HPP cannot provide electricity in autumn and winter. Due to the fact that an average of 11 billion m3 of water per year from the Toktogul reservoir used to irrigate the territories of Uzbekistan, Tajikistan and Kazakhstan. Under such conditions, Kyrgyzstan faces difficulties in managing the water regime of the Toktogul HPP due to a decrease in electricity supply in the winter.

At the same time, population growth observed in Kyrgyzstan, new houses and enterprises are being built. The expansion of irrigated lands is becoming an urgent task, the solution of which is necessary to provide the growing population with agricultural products.

3 Formulation of the Problem

The paper sets the task to investigate the hydrological regime of the upper reaches of the Naryn River (Narynhydropost, Naryn city) since 1930. Therefore, it is necessary to modernize and develop the systems of water supply, energy and water resources management. In this regard, one of the most important scientific and practical issues is the hydrological analysis of the flow of the Naryn River and the forecast of fluctuations in water content in the Toktogul reservoir to optimize the cost-effective operation of the Toktogul HPP.

4 Theoretical Part

The distribution of runoff within a year determined by the time when water enters the river system from genetic sources—snow, glaciers and rains. In the conditions of Kyrgyzstan, regulated by the peculiarities of orography and relief—the distribution of watershed areas in altitudinal zones and exposures—relative to moisture-bearing air masses, synoptic conditions of the cold and warm periods of the year.

Many scientists have developed theoretical foundations and methods for studying the hydrological characteristics of the rivers of Kyrgyzstan, including the Naryn river basin. These include V.L. Schultz “Rivers of Central Asia”, 1965, D.M. Mamatkanov “Modeling and prediction of fluctuations in river flow”, 1973, M.N. Bolshakov “Water resources of the rivers of the Soviet Tien Shan and methods for their calculation”, 1974, S.K. Alamanov “Study of the formation and long-term forecast of river flow in the north-west of Kyrgyzstan”, 1977, A.G. Grinevich, E.K. Pospaeva “Characteristics of vegetation runoff in the basin of the river. Naryn and questions of its forecasting”, 1975, I.V. Ratsek “Oscillations and evolution of glacial runoff in the basin of the river. Naryn”, 1991.

5 Practical Significance, Suggestions and Results of Implementations

To assess the situation in the upper reaches of the Naryn River, hydrological and meteorological data from the archive of the Hydrometeorological Service of the Kyrgyz Republic used for the period 1930–2020. Were applied Statistical, geographical and hydrological methods.

According to the data of the gauging station in the city of Naryn for 1930–2020, it can be seen that the average water discharge for the growing season has increased since 1992 (Fig. 1). So, if the average vegetation flow in 1931–1991 was 144.7 m3/s, later for the period from 1992 to 2020 it increased to 173.9 m3/s, or by 120%.

Fig. 1
A line graph of average vegetative water consumption of the river Naryn in Naryn city versus year. All data are estimated. A line trend increases from (1930, 140) to (2020, 170). Another line fluctuates along the increasing line trend.

Changes in water discharge on the river Naryn (hydropostNaryn from 1930 to 2020)

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The study of the Naryn River's feeding sources during the growing season showed that in upper reaches the increasing of water inflow in April-June occurs mainly due to snow melting, and in July–September—due to ice and high-mountain snow melting [5,6,7]. Calculations based on data for 1992–2020 showed that the ratio of the water content of the Naryn River by months of the growing season distributed as follows: 26% of the flow fell on July, 23% on June and August, 13% on May, 10% on September and 5% in April, as seen in Fig. 2.

Fig. 2
A 3-D bar graph of water content in percentage versus months in Roman numerals from 4 to 9. The graph data are as follows. 4, 5. 5, 13. 6, 23. 7, 26. 8, 23. 9, 10.

Percentage of monthly runoff to vegetation runoff (Naryn gauging station)

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The results of analyze Fig. 3, show that the supply of the river with glacial water decreased compared to its supply with snow water (Fig. 3). Since 1992, the part of the July runoff in the vegetation season of the total runoff has decreased by 10%, (Fig. 4). According to V.A. Kuzmichenok and A.N. Dikikh [7,8,9], the relative decrease of glacial water part in the river associated with a decreasing of the glacier’s area and the attraction of the lower boundary of the firn upwards. In August, the share of runoff did not change, while in September, on the contrary, it increased (about 1%). As shown on Fig. 4 the share of river feeding by melt waters (April-June), on the contrary, increases. Following this trend, the maximum water inflow gradually shifts from July to May–June.

Fig. 3
A line graph of water consumption versus year. The lines of April to June and July to September fluctuate along 2 increasing trends.

The ratio of the river's supply of melted snow water (April–June) and melted glacial water (July–September)

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Fig. 4
A line graph of the share of monthly runoff versus year. The lines, 4, 9, and 8 in Roman numerals fluctuate along 3 increasing trends. The line, 5 in Roman numerals fluctuates along a horizontal trend. The lines, 7 and 6 in Roman numerals fluctuate along 2 decreasing trends.

Changes in the share of monthly runoff in the total runoff of the vegetation season

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The temperature regime of the summer months and precipitation falling on the river catchment during the cold season play a key role in the formation of long-term runoff fluctuations during the vegetation season. In other words, climatic factors determine the formation of runoff [10,11,12,13]. For example, over the past 20 years, compared with 1930–1999 [14, 15], the amount of precipitation in the cold seasons of the year has increased, (Fig. 5). So, in October–April in 1930-2019p Precipitation in the upper reaches of the Naryn River increased from 646.8 mm to 1168 mm at the Tien Shan meteorological station and from 977.5 to 1401.8 mm at the Naryn meteorological station. As a result, the flow of the Naryn River also increased [16], as shown in Fig. 1. A.N. Dikikh [7] noted a decrease in the water level in the upper reaches of the Naryn River due to a precipitation decrease during the cold periods of the year in 1930–1998.

Fig. 5
2 3-D bar graphs of precipitation versus year. The highest and lowest values are as follows. 1, at Naryn, 2010 to 2019, 1401.8. 1930 to 1939, 977.5. 2, at Tien Shan, 2010 to 2019, 1168. 1930 to 1939, 646.8.

Changes for precipitation (in mm) from October to April at Naryn and Tien Shan weather stations

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Analyzing the data of the Naryn and Tien Shan weather stations, we notice climatic conditions changes in the upper reaches of the Naryn River over the past 20–40 years [6].

The sum of positive air temperatures at the Tien Shan weather station increased from 95.4 to 168.7 °C, at the Naryn weather station from 827.4 to 947 °C (Fig. 6).

Fig. 6
2 3-D bar graphs of the sum of positive air temperatures versus year plot an increasing trend. The highest and lowest values are as follows. 1, at Naryn, 2010 to 2019, 947. 1930 to 1939, 827.4. 2, at Tien Shan, 2010 to 2019, 168.7. 1930 to 1939, 95.4.

Sum of average annual positive air temperatures at Naryn and Tien Shan weather stations

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The number of days with positive temperatures also increased. For example, in the high mountain zone over the past 20 years it increased from 109 to 122 days, and in the middle mountain zone of the river—from 220 to 236 days over the past 40 years. As a result, the air temperature above 0 °C shifted from mid-May–June to April–May at the Tien-Shan weather station, from mid-March to the first half of March at the Naryn weatherl station [17, 18].

The analysis of the average annual water consumption at the Naryn hydropost and the correlations of the average monthly air temperatures at the Naryn and Tien Shan weather stations showed that the correlation between summer air temperatures and runoff at the Tien Shan weather station is very close (Fig. 7). According to O. Yu Kalashnikova. Studies [19, 20], the summer runoff of the upper reaches of the Naryn River during the vegetation season was 72% of the annual volume. In the summer months, the tendency of the air temperature raised. At the Tien Shan weather station, the air temperature in the summer months of 1930–2019 increased by 1.2 °C (Fig. 8). In the summer months, there is a tendency to increase the air temperature.

Fig. 7
A scatterplot of average vegetation water consumption versus average air temperature. The plots are scattered on either side of an increasing trend. The equations indicated on the graph are y = 23.199 x + 69 and R squared = 0.2962.

Dependence of the average vegetation water consumption at the Naryn hydropost on the average air temperature in June-August at the Tien Shan weather station

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Fig. 8
A line graph of air temperature in June to August versus year. The line fluctuates along an increasing line trend.

Changes in the average air temperature in June–August according to the data of the Tien Shan weather station

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In addition to climatic parameters, the vegetation period of runoff is influenced by low water flow (October–March) Fig. 9. For example, Fig. 10 shows that the low water flow runoff has been increasing since 1992. The low water flow runoff was 29.9 m3/s in 1931–1991 and increased by 37.7 m3/s or 120% in the period from 1992 to 2017.

Fig. 9
A scatterplot of average vegetation water consumption versus low water flow runoff. The plots are scattered on either side of an increasing trend. The equations indicated on the graph are y = 3.4149 x + 62.503 and R squared = 0.2474.

Dependence of the average vegetation water consumption at the Naryn hydropost on the average water consumption during the low water flow runoff period

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Fig. 10
A line graph of water consumption versus years. The line fluctuates along an increasing line trend.

Change in water consumption of the Naryn hydropost during the low water flow runoff period (m3/s)

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6 Conclusion

Since 1992, according to the data of the Narynhydro postwater discharges increased in the upper reaches of the Naryn River. The average vegetation period runoff was 144.7 m3/s in 1931–1991, and over the period from 1992 to 2017 it increased by 173.9 m3/s or 120%. In 1992–2017, the share of runoff in July (powered by melting glaciers) decreased by 10% at the Narynhydro post. In 1930–2019, in the upper reaches of the Naryn River, the amount of precipitation in October–April increased from 646.8 to 1168 mm at the Tien Shan weather station and from 977.5 to 1401.8 mm at the Naryn weather station. The sum of positive air temperatures at the Tien Shan weather station increased from 95.4 to 168.7 °C, and at the Narynweather station from 827.4 to 947 °C.