1. Introduction
One of the most characteristic indicators of climate change is the melting of glaciers: since the beginning of the 20th century, more than 20% of European glaciers have disappeared over the past 30 years
[1]
Understanding what is happening to glaciers is necessary in order to predict changes in the water balance of territories. This is especially true for regions where melting glaciers are a source of fresh water.
The IPCC report
[2][3][4][5][6][7]
In this regard, of particular interest is the study of modern changes in seasonal and regional climate and its impact on the processes occurring in the cryosphere, leading to the melting of glaciers in the high mountain regions of the Caucasus.
2. Research methods and principles
To determine the climatic characteristics (seasonal temperatures, precipitation) affecting the glaciers of the Baksan River basin (Bolshoi Azau, Irik, Shkhelda, etc.), series of observations at the Terskol weather station (2144 m) were used as the main source of information (archive of the Elbrus anti-avalanche team of the North Caucasian paramilitary service for active influence on hydrometeorological processes).
The assessment of the coefficients of linear trends of meteorological parameters was obtained by the least squares method and expressed in °C/10 years and in mm/month/10 years. The significance of the trend is determined by the value of the coefficient of determination
where
The tabular value of the Fisher criterion (
3. Main results
According to the Terskol weather station (Kabardino-Balkaria, 2144 m above sea level, a high-mountain region with a pronounced continental climate and vertical zonation), the average annual temperature for 1961-2021 was 2.64°C with a climatic norm of 2.54°C (average for 1961-1990). Unlike the winter, spring and autumn seasons, in the summer seasons 1961-2021 average temperatures in Terskol had a positive significant trend. The rate of increase in summer temperatures for the period 1961-2021 was 0.32°C/10 years (D=39%), increasing from 1976 to 0.43°C/10 years (D=44%, the maximum of all seasonal trends). It is noted in
[5]
In the period since 1976 there has been a statistically significant rate of increase in average annual temperature by b=0.2°C/10 years with a high contribution to the explained variance of D=17%. With the increase in the duration of the subperiods (1976-2013, 1976-2014,….., 1976-2021), the rate of increase in the annual temperature of the Terskol weather station increased, approaching statistically significant: in 1976-2013 by 0.06 °C/10 years (D=3%); in 1976-2014 by 0.11°C/10 years (D=4%);…; in 1976-2021 by 0.20°C/10 years (D=17%).
When highlighting the sub-period 2001-2021, characterized by increased melting of the Caucasus glaciers, from Figure 1 it can be noted that the rate of increase in annual temperature in Terskol increased to 0.70°C/10 years (D=32.9%, FfactMissing Mark : sub.=8 .97> Ftheor.Missing Mark : sub=4.67 for df =20, which defines the trend of average annual temperatures as statistically significant). There was also an increase in the increase in winter (0.16°C/year, D=25.1%) and spring (0.08°C/10 years, D=23.4%) temperatures to a statistically significant level. Summer temperatures continue to rise, but the trend is statistically insignificant (0.04°C/year, D=14.3%). Thus, over the past 20 years, in the winter, spring and summer seasons, there has been an increase in temperatures at a significant level of warming, comparable to other climatic zones.
Average temperature graphs (Terskol) with trends in sub-periods 1976-2000 (y1) and 2001-2021 (y2)
From Table 1 it can be seen that in the period from 2001 to 2021 against the background of a significant increase in seasonal temperatures, changes in the amount of precipitation, both seasonal and annual, had negative trends, all trends were statistically insignificant (Table 1).
Parameters of changes in precipitation, Terskol
To calculate changes in the water balance during the degradation of valley glaciers in the Central Caucasus, glaciers of the Baksan River basin were selected in order to assess the impact of mountain climate change according to data from the Terskol weather station, located in the Baksan Gorge. From data on the degradation of valley glaciers of the Greater Caucasus, given by Dokukin M.D. in
[8]
According to the recommendation of the authors
[8]
∆V= ∆S.h = 6.35 km2 .Missing Mark : sup 0.075 km = 0.47625 .Missing Mark : sup 109Missing Mark : sup m3Missing Mark : sup
or taking into account the fact that 1 m3Missing Mark : sup = 1 ton of water,
mass of water: m=476250000 tons.
Thus, over the past 60 years, as a result of the melting of the Great Azau glacier (Central Caucasus, Baksan River basin), the water balance has decreased by 476.25 million tons.
To compare the rate of melting, we present the results of calculations on changes in the water balance of the Bolshoy Azau and Terskol glaciers over the past 20 years (from 1997 to 2017), using data on changes in the volume of the ice shell (∆V, km3Missing Mark : sup) from the paper of Kutuzov S.S.
[9]
Decrease in water balance as a result of the melting of the Greater Azau glacier from 1997 to 2017 the average amounted to 260 million tons, which is more than half the value of 476.25 million tons (decrease from 1957 to 2020).
For the remaining glaciers of the River Baksan basin, the decrease in their water balance as a result of melting from 1957 to 2020 is presented in Table 2. From Table 2 it can be seen that the second-largest reduction in the water balance for the period 1957-2020 occurred due to the melting of the Kayaartybashi glacier. The average value was 92.25 million tons, with a maximum decrease of 98.25 million tons and a minimum of 86.25 million tons. From 1957 to 2020 on the Chegetkarachiran glacier, the average decrease was 2.26 million tons of water (from a maximum of 2.40 million tons to a minimum of 2.10 million tons). Shhelda Glacier lost an average of 93 million tons of water reserves for the period from 1960 to 2020, and the Bolshoi Tyutyu glacier – 44.25 million tons (from 1962 to 2020).
Decrease in the water balance of glaciers as a result of melting
4. Discussion
The problem with such intense glacier melting is its consequences. As glaciers shrink in response to a warming climate, water is released from long-term glacial reserves. At first, glacial runoff increases, but after a few years or decades there will be a tipping point, often called "peak water," after which glacial runoff, and therefore its contribution to downstream streamflow, will decrease.
Global modeling results show that peak water was reached before 2019 for 55-67% of glaciers in Central Europe and the Caucasus
[10][11]
5. Conclusion
Climate change and the resulting glacier degradation continue, and the pace of these processes is increasing. Since the beginning of the current century, in Terskol in the winter, spring and summer seasons there has been an increase in temperatures at a significant level of warming, comparable to other climatic zones. This seasonal increase in temperature has generated a statistically significant increase in the average annual temperature at the Terskol station in the last 20 years (0.07°C/year, D=32.9%). Between 2001 and 2021 against the background of a significant increase in seasonal temperatures, the total precipitation, both seasonal and annual, had negative trends, all trends were statistically insignificant.
The prevailing thermal and precipitation regimes in recent decades have been the main component of many factors leading to a reduction in the area of glaciers and changes in the water balance.
In total, over the past 60 years, the glaciers of the river basin Baksan have lost 844.51 million tons of water, of which the Bolshoi Azau glacier accounted for 476.25 million tons of water. Over the past 20 years, Greater Azau has lost 260 million tons of water, which accounted for more than half of the losses in a third of the time of the entire studied period, which probably happened with all other glaciers of the Caucasus.