What is happening with the Caspian Sea. When the Caspian Sea disappears
Lay comments by some academic experts on Iran are sometimes made on the creation of a canal to carry water from the Caspian to the desert (Dasht-e Kavir) more to argue whether the world's largest lake is waning? There is no doubt that the Hyrcanian forests and glaciers that arose thirty million years ago, which have no analogues in the Alborz (Elbrus) mountains, biodiversity and ecosystems on the southern coast of the Caspian Sea, influenced the role of the Caspian Sea.In recent years, there have been various rumors about the transfer of sea water to the arid regions of Iran and Lake Urmia (which is shrinking). Again, more closed marine environmental issues were noted between Kazakhstan, Turkmenistan, Azerbaijan and Russia.
The construction of a canal to transfer water from the Caspian Sea to the sea will create many problems in residential areas, plant and animal species, marine habitats and coastal economies of the five coastal countries.
Immigration, severe pollution caused by harmful salts and minerals, various diseases, birth defects, reduction of arable land, salt formation, as well as political, economic and social anomalies, etc. threaten public order. And the countries of the Caspian region may face fundamental problems.
There is no impression that Kazakhstan would much like to transfer water from the sea of Iran to the Aral Lake or Turkmenistan, the territory of which is a desert, where sea water can be used for agriculture. With such an approach, the fate of the Caspian Sea can become similar to the Aral Sea. The Aral is located between two countries, Kazakhstan and Uzbekistan.
On the other hand, if you connect such a channel as the Volga-Donskoy with the Caspian Sea, the Persian Gulf, there will be an influx of invasive species of aquatic organisms, which will destroy the ecosystem of the Caspian Sea.
Given all these interpretations, the most logical solution to address the major dehydration problems in Iran and other dry Caspian littoral states is not to transfer water from the Caspian Sea, but rather to cooperate with the Caspian littoral states and NGOs in the field of culture and education. It is necessary to use world experience on the issue of water shortage to supply water to agriculture and industry. For example, seeding clouds, planting drought-resistant plants, etc. V. N. MIKHAILOV
The Caspian Sea is the largest drainless lake on the planet. This body of water is called the sea for its huge size, brackish water and sea-like regime. The level of the Caspian Sea-lake lies much lower than the level of the World Ocean. At the beginning of 2000, he had a mark of about - 27 abs. m. At this level, the area of the Caspian Sea is ~ 393 thousand km2 and the volume of water is 78,600 km3. The average and maximum depths are 208 and 1025 m, respectively.
The Caspian Sea is elongated from south to north (Fig. 1). The Caspian washes the shores of Russia, Kazakhstan, Turkmenistan, Azerbaijan and Iran. The reservoir is rich in fish, its bottom and banks are rich in oil and gas. The Caspian Sea is quite well studied, but many mysteries remain in its regime. The most characteristic feature of the reservoir is the instability of the level with sharp drops and rises. The last rise in the level of the Caspian took place before our eyes from 1978 to 1995. It gave rise to many rumors and speculation. Numerous publications appeared in the press, which spoke about catastrophic floods and ecological catastrophe. It was often written that the rise in the level of the Caspian Sea led to the flooding of almost the entire Volga delta. What is true in the statements made? What is the reason for such behavior of the Caspian Sea?
WHAT HAPPENED TO THE CASPIAN IN THE 20TH CENTURY
Systematic observations over the level of the Caspian Sea were started in 1837. In the second half of the 19th century, the average annual values of the Caspian Sea level were in the range of marks from -26 to -25.5 abs. m and showed a slight downward trend. This trend continued into the 20th century (Fig. 2). In the period from 1929 to 1941, the sea level dropped sharply (by almost 2 m - from - 25.88 to - 27.84 abs. m). In subsequent years, the level continued to fall and, having decreased by approximately 1.2 m, reached in 1977 the lowest mark for the observation period - 29.01 abs. m. Then the sea level began to rise rapidly and, having risen by 2.35 m by 1995, reached a mark of 26.66 abs. m. In the next four years, the average sea level decreased by almost 30 cm. Its average marks were 26.80 in 1996, 26.95 in 1997, 26.94 in 1998 and 27.00 abs. m in 1999.
The decrease in sea level in the years 1930-1970 led to the shallowing of coastal waters, the extension of the coastline towards the sea, and the formation of wide beaches. The latter was perhaps the only positive consequence of the level drop. There were many more negative consequences. With a decrease in the level, the areas of forage land for fish stocks in the northern Caspian have decreased. The shallow estuarine coast of the Volga began to quickly overgrow with aquatic vegetation, which worsened the conditions for the passage of fish to spawn in the Volga. Catches of fish, especially valuable species such as sturgeon and sterlet, have sharply decreased. Shipping began to suffer damage due to the fact that the depths in the approach channels decreased, especially near the Volga delta.
The rise in the level from 1978 to 1995 was not only unexpected, but also led to even greater negative consequences. After all, both the economy and the population of coastal areas have already adapted to a low level.
Many sectors of the economy began to suffer damage. Significant territories turned out to be in the zone of flooding and flooding, especially in the northern (flat) part of Dagestan, in Kalmykia and the Astrakhan region. The cities of Derbent, Kaspiysk, Makhachkala, Sulak, Caspian (Lagan) and dozens of other smaller settlements suffered from the level rise. Significant areas of agricultural land have been flooded and flooded. Roads and power lines, engineering structures of industrial enterprises and public utilities are being destroyed. A threatening situation has developed with fish-breeding enterprises. Abrasion processes in the coastal zone and the effect of sea water surges have intensified. In recent years, the flora and fauna of the seashore and the coastal zone of the Volga delta suffered significant damage.
In connection with the increase in depth in the shallow waters of the Northern Caspian and the reduction in the areas occupied in these places by aquatic vegetation, the conditions for the reproduction of stocks of anadromous and semi-anadromous fish and the conditions for their migration to the delta for spawning have somewhat improved. However, the predominance of negative consequences from the rising sea level made us speak of an ecological catastrophe. The development of measures to protect national economic objects and settlements from the advancing sea began.
HOW UNUSUAL IS CURRENT CASPIAN BEHAVIOR?
Research into the life history of the Caspian Sea can help answer this question. Of course, there are no direct observations of the past regime of the Caspian Sea, but there are archaeological, cartographic and other evidence for historical time and the results of paleogeographic studies covering a longer period.
It is proved that during the Pleistocene (the last 700-500 thousand years) the level of the Caspian Sea underwent large-scale fluctuations in the range of about 200 m: from -140 to + 50 abs. m. In this period of time in the history of the Caspian, four stages are distinguished: Baku, Khazar, Khvalyn and New Caspian (Fig. 3). Each stage included several transgressions and regressions. The Baku transgression occurred 400-500 thousand years ago, the sea level rose to 5 abs. m. During the Khazar stage, there were two transgressions: the early Khazar (250-300 thousand years ago, the maximum level is 10 abs. m) and the late Khazar (100-200 thousand years ago, the highest level is 15 abs. m). The Khvalyn stage in the history of the Caspian included two transgressions: the largest for the Pleistocene period, the early Khvalyn (40-70 thousand years ago, the maximum level is 47 abs. m, which is 74 m higher than the modern one) and the late Khvalyn (10-20 thousand years ago, the rise level up to 0 abs. m). These transgressions were separated by a deep Enotaevskaya regression (22-17 thousand years ago), when the sea level dropped to -64 abs. m and was 37 m lower than the modern one.
Rice. 4. Fluctuations in the level of the Caspian Sea over the past 10 thousand years. P is the natural range of fluctuations in the level of the Caspian Sea under climatic conditions characteristic of the subatlantic epoch of the Holocene (risk zone). I-IV - stages of the New Caspian transgression; M - Mangyshlak, D - Derbent regression
Significant fluctuations in the level of the Caspian also occurred during the New Caspian stage of its history, which coincided with the Holocene (the last 10 thousand years). After the Mangyshlak regression (10 thousand years ago, a level decrease to -50 abs. m), five stages of the New Caspian transgression were noted, separated by small regressions (Fig. 4). Following sea level fluctuations, its transgressions and regressions, the outline of the reservoir also changed (Fig. 5).
Over the historical time (2000 years), the range of changes in the average level of the Caspian Sea was 7 m - from - 32 to - 25 abs. m (see Fig. 4). The minimum level in the last 2000 years was during the Derbent regression (VI-VII centuries AD), when it decreased to - 32 abs. m. During the time that has passed since the Derbent regression, the average sea level has changed in an even narrower range - from -30 to -25 abs. m. This range of level changes is called the risk zone.
Thus, the level of the Caspian has experienced fluctuations before, and in the past they were more significant than in the 20th century. Such periodic fluctuations are a normal manifestation of the unstable state of a closed reservoir with variable conditions at the outer boundaries. Therefore, there is nothing unusual in the lowering and rising of the level of the Caspian Sea.
Fluctuations in the level of the Caspian Sea in the past, apparently, did not lead to the irreversible degradation of its biota. Of course, sharp drops in sea level created temporary unfavorable conditions, for example, for fish stocks. However, with the rise in the level, the situation corrected itself. The natural conditions of the coastal zone (vegetation, benthic animals, fish) experience periodic changes along with fluctuations in sea level and, apparently, have a certain margin of stability and resistance to external influences. After all, the most valuable sturgeon herd has always been in the Caspian basin, regardless of fluctuations in sea level, quickly overcoming the temporary deterioration of living conditions.
Rumors that rising sea levels have caused flooding throughout the Volga Delta have not been confirmed. Moreover, it turned out that the increase in water levels, even in the lower part of the delta, is inadequate to the magnitude of the sea level rise. The increase in the water level in the lower part of the delta during the low water period did not exceed 0.2-0.3 m, and almost did not manifest itself during the flood. At the maximum level of the Caspian Sea in 1995, the backwater from the sea extended along the deepest branch of the Bakhtemir delta by no more than 90 km, and along other branches by no more than 30 km. Therefore, only islands on the seashore and a narrow coastal strip of the delta were flooded. Flooding in the upper and middle parts of the delta was associated with high floods in 1991 and 1995 (which is normal for the Volga delta) and with the unsatisfactory condition of protective dams. The reason for the weak effect of sea level rise on the regime of the Volga delta is the presence of a huge shallow coastal zone, which dampens the effect of the sea on the delta.
With regard to the negative impact of sea level rise on the economy and life of the population in the coastal zone, the following should be recalled. At the end of the last century, the sea level was higher than at present, and this was not perceived as an ecological disaster. And before the level was even higher. Meanwhile, Astrakhan has been known since the middle of the 13th century, and Sarai-Batu, the capital of the Golden Horde, was located here in the 13th - mid-16th centuries. These and many other settlements on the Caspian coast did not suffer from high level standing, since they were located on elevated places and during abnormal flood levels or surges, people temporarily moved from low places to higher ones.
Why, then, are the consequences of a rise in sea level even to smaller levels now perceived as a catastrophe? The reason for the enormous damage that the national economy suffers is not the rise in the level, but the thoughtless and short-sighted development of a strip of land within the mentioned risk zone, freed (as it turned out, temporarily!) From under the sea level after 1929, that is, with a decrease in the level below the mark - 26 abs. m. The buildings erected in the risk zone, of course, turned out to be flooded and partially destroyed. Now, when the territory developed and polluted by man is flooded, a dangerous ecological situation is really created, the source of which is not natural processes, but unreasonable economic activity.
ABOUT THE REASONS FOR THE CASPIAN LEVEL VARIATIONS
Considering the issue of the causes of fluctuations in the level of the Caspian Sea, it is necessary to pay attention to the confrontation in this area of two concepts: geological and climatic. Significant contradictions in these approaches were revealed, for example, at the international conference "Caspian-95".
According to the geological concept, two groups of processes are attributed to the causes of changes in the level of the Caspian Sea. The processes of the first group, according to geologists, lead to a change in the volume of the Caspian depression and, as a result, to changes in sea level. Such processes include vertical and horizontal tectonic movements of the earth's crust, accumulation of bottom sediments, and seismic events. The second group includes processes that, as geologists believe, affect the underground runoff into the sea, either increasing it or decreasing it. Such processes are called periodic extrusion or absorption of water, which saturate bottom sediments under the influence of changing tectonic stresses (changes in periods of compression and tension), as well as technogenic destabilization of the subsoil due to oil and gas production or underground nuclear explosions. It is impossible to deny the fundamental possibility of the influence of geological processes on the morphology and morphometry of the Caspian depression and underground runoff. However, at present, the quantitative relationship of geological factors with fluctuations in the level of the Caspian Sea has not been proven.
There is no doubt that tectonic movements played a decisive role in the initial stages of the formation of the Caspian depression. However, if we take into account that the Caspian Sea basin is located within a geologically heterogeneous territory, which results in a periodic rather than linear nature of tectonic movements with repeated sign changes, then one should hardly expect a noticeable change in the capacity of the basin. Not in favor of the tectonic hypothesis is the fact that the coastlines of the New Caspian transgressions in all sections of the Caspian coast (with the exception of certain areas within the Apsheron archipelago) are at the same level.
There are no grounds to consider the change in the capacity of its basin due to the accumulation of precipitation as the reason for fluctuations in the level of the Caspian Sea. The rate of filling the basin with bottom sediments, among which the main role is played by river discharges, is estimated, according to modern data, at a value of about 1 mm/year or less, which is two orders of magnitude less than the currently observed changes in sea level. Seismic deformations, which are noted only near the epicenter and attenuate at close distances from it, cannot have any significant effect on the volume of the Caspian Basin.
As for the periodic large-scale discharge of groundwater into the Caspian Sea, its mechanism is still unclear. At the same time, this hypothesis is contradicted, according to E.G. Maev, firstly, the undisturbed stratification of interstitial waters, indicating the absence of noticeable migrations of waters through the thickness of bottom sediments, and secondly, the absence of proven powerful hydrological, hydrochemical and sedimentation anomalies in the sea, which should have accompanied a large-scale discharge of groundwater capable of affect changes in water levels.
The main evidence of the insignificant role of geological factors at present is the convincing quantitative confirmation of the plausibility of the second, climatic, or rather, water-balance concept of Caspian level fluctuations.
CHANGES IN THE COMPONENTS OF THE CASPIAN WATER BALANCE AS THE MAIN CAUSE OF ITS LEVEL FLUCTUATIONS
For the first time, fluctuations in the level of the Caspian Sea were explained by changes in climatic conditions (more specifically, river runoff, evaporation and precipitation on the sea surface) by E.Kh. Lenz (1836) and A.I. Voeikov (1884). Later, the leading role of changes in the components of the water balance in sea level fluctuations was again and again proved by hydrologists, oceanologists, physicogeographers and geomorphologists.
The key to most of the studies mentioned is the compilation of the water balance equation and the analysis of its components. The meaning of this equation is as follows: the change in the volume of water in the sea is the difference between the incoming (river and underground runoff, atmospheric precipitation on the sea surface) and outgoing (evaporation from the sea surface and outflow of water into the Kara-Bogaz-Gol Bay) components of the water balance. The change in the level of the Caspian is the quotient of dividing the change in the volume of its waters by the area of the sea. The analysis showed that the leading role in the water balance of the sea belongs to the ratio of the flow of the Volga, Ural, Terek, Sulak, Samur, Kura rivers and visible or effective evaporation, the difference between evaporation and atmospheric precipitation on the sea surface. An analysis of the components of the water balance revealed that the largest contribution (up to 72% of the dispersion) to the level variability comes from the inflow of river waters, and more specifically, the runoff formation zone in the Volga basin. As for the reasons for the change in the flow of the Volga itself, they are associated, as many researchers believe, with the variability of atmospheric precipitation (mainly winter) in the river basin. And the mode of precipitation, in turn, is determined by the circulation of the atmosphere. It has long been proven that the latitudinal type of atmospheric circulation contributes to an increase in precipitation in the Volga basin, while the meridional type contributes to a decrease.
V.N. Malinin revealed that the root cause of moisture entering the Volga basin should be sought in the North Atlantic, and specifically in the Norwegian Sea. It is there that the increase in evaporation from the sea surface leads to an increase in the amount of moisture transferred to the continent, and, accordingly, to an increase in precipitation in the Volga basin. The latest data on the water balance of the Caspian Sea, received by the staff of the State Oceanographic Institute R.E. Nikonova and V.N. Bortnik, are given with the author's clarifications in Table. 1. These data convincingly prove that the main reasons for both the rapid drop in sea level in the 1930s and the sharp rise in 1978-1995 were changes in river flow, as well as apparent evaporation.
Keeping in mind that river runoff is one of the main factors affecting the water balance and, as a result, the level of the Caspian Sea (and the Volga runoff provides at least 80% of the total river runoff to the sea and about 70% of the incoming part of the Caspian water balance), it would be interesting to find a connection between sea level and the flow of one Volga, measured most accurately. Direct correlation of these quantities does not give satisfactory results.
However, the relationship between the sea level and the Volga runoff is well traced if the river runoff is not taken into account for each year, but the ordinates of the difference integral runoff curve are taken, that is, the sequential sum of the normalized deviations of the annual runoff values from the long-term average value (norm). Even a visual comparison of the course of the average annual levels of the Caspian Sea and the difference integral curve of the Volga runoff (see Fig. 2) makes it possible to reveal their similarity.
For the entire 98-year period of observations of the Volga runoff (the village of Verkhneye Lebyazhye at the head of the delta) and the sea level (Makhachkala), the correlation coefficient of the relationship between the sea level and the ordinates of the difference integral runoff curve was 0.73. If we discard years with small level changes (1900-1928), then the correlation coefficient increases to 0.85. If for analysis we take a period with a rapid decline (1929-1941) and a rise in the level (1978-1995), then the overall correlation coefficient will be 0.987, and separately for both periods 0.990 and 0.979, respectively.
The presented calculation results fully confirm the conclusion that during periods of a sharp decrease or increase in sea level, the levels themselves are closely related to the runoff (more precisely, to the sum of its annual deviations from the norm).
A special task is to assess the role of anthropogenic factors in fluctuations in the level of the Caspian Sea, and above all, the reduction in river flow due to its irretrievable losses for filling reservoirs, evaporation from the surface of artificial reservoirs, and water withdrawal for irrigation. It is believed that since the 1940s, irretrievable water consumption has been steadily increasing, which has led to a reduction in the inflow of river waters to the Caspian Sea and an additional decrease in its level compared to the natural one. According to V.N. Malinin, by the end of the 1980s, the difference between the actual sea level and the restored (natural) level reached almost 1.5 m. about 26 km3/year). If it were not for the withdrawal of river runoff, then the rise in sea level would have begun not at the end of the 70s, but at the end of the 50s.
The increase in water consumption in the Caspian basin by 2000 was predicted first to 65 km3/year, and then to 55 km3/year (36 of them were in the Volga). Such an increase in irretrievable losses of river runoff should have lowered the level of the Caspian by more than 0.5 m by 2000. In connection with the assessment of the impact of irreversible water consumption on the level of the Caspian, we note the following. First, estimates of water withdrawal volumes and evaporation losses from the surface of reservoirs in the Volga basin found in the literature seem to be significantly overestimated. Secondly, forecasts of water consumption growth turned out to be erroneous. The forecasts included the rate of development of water-consuming sectors of the economy (especially irrigation), which not only turned out to be unrealistic, but also gave way to a decline in production in recent years. In fact, as A.E. Asarin (1997), by 1990 water consumption in the Caspian basin was about 40 km3/year, and has now decreased to 30-35 km3/year (in the Volga basin to 24 km3/year). Therefore, the "anthropogenic" difference between the natural and actual sea levels is currently not as large as predicted.
ON POSSIBLE FLUCTUATIONS OF THE CASPIAN LEVEL IN THE FUTURE
The author does not set himself the goal of analyzing in detail the numerous forecasts of fluctuations in the level of the Caspian Sea (this is an independent and difficult task). The main conclusion from the assessment of the results of forecasting fluctuations in the level of the Caspian can be drawn as follows. Although the forecasts were based on completely different approaches (both deterministic and probabilistic), there was not a single reliable forecast. The main difficulty in using deterministic forecasts based on the sea water balance equation is the lack of development of the theory and practice of ultra-long-term forecasts of climate change over large areas.
When the sea level decreased in the 1930s and 1970s, most researchers predicted its further fall. In the last two decades, when sea level rise began, most forecasts predicted an almost linear and even accelerating rise in level to -25 and even -20 abs. m and above at the beginning of the XXI century. In this case, three factors were not taken into account. First, the periodic nature of fluctuations in the level of all endorheic reservoirs. The instability of the Caspian level and its periodic nature are confirmed by the analysis of its current and past fluctuations. Secondly, at sea level close to - 26 abs. m, the flooding of large sor bays on the northeastern coast of the Caspian Sea - Dead Kultuk and Kaydak, as well as low-lying areas in other places of the coast, dried up at a low standing level, will begin. This would lead to an increase in the area of shallow waters and, as a consequence, an increase in evaporation (up to 10 km3/year). With a higher sea level, the outflow of water to Kara-Bogaz-Gol will increase. All this should stabilize or at least slow down the level growth. Thirdly, level fluctuations under the conditions of the modern climatic epoch (the last 2000 years), as shown above, are limited by the risk zone (from -30 to -25 abs. m). Taking into account the anthropogenic decrease in runoff, the level is unlikely to exceed the mark of 26-26.5 abs. m.
The decrease in average annual levels in the last four years by a total of 0.34 m, possibly indicates that in 1995 the level reached its maximum (-26.66 abs. m), and a change in the trend of the Caspian level. In any case, the prediction that sea level is unlikely to exceed 26 abs. m, apparently justified.
In the 20th century, the level of the Caspian Sea changed within 3.5 m, first dropping and then rising sharply. Such behavior of the Caspian Sea is the normal state of a closed reservoir as an open dynamic system with variable conditions at its inlet.
Each combination of incoming (river runoff, precipitation on the sea surface) and outgoing (evaporation from the surface of the reservoir, outflow to the Kara-Bogaz-Gol Bay) components of the Caspian water balance corresponds to its own level of equilibrium. Since the components of the water balance of the sea also change under the influence of climatic conditions, the level of the reservoir fluctuates, trying to reach an equilibrium state, but never reaches it. Ultimately, the trend in the level of the Caspian Sea at a given time depends on the ratio of precipitation minus evaporation in the catchment area (in the basins of the rivers that feed it) and evaporation minus precipitation over the reservoir itself. There is really nothing unusual about the recent rise of the Caspian Sea level by 2.3 m. Such level changes have occurred many times in the past and did not cause irreparable damage to the natural resources of the Caspian. The current rise in sea level has become a catastrophe for the economy of the coastal zone only because of the unreasonable development of this risk zone by man.
Vadim Nikolaevich Mikhailov, Doctor of Geographical Sciences, Professor of the Department of Terrestrial Hydrology of the Faculty of Geography of Moscow State University, Honored Worker of Science of the Russian Federation, full member of the Academy of Water Management Sciences. Area of scientific interests - hydrology and water resources, interaction of rivers and seas, deltas and estuaries, hydroecology. Author and co-author of about 250 scientific papers, including 11 monographs, two textbooks, four scientific and methodological manuals.
The Caspian Sea is so named for its large size, but from a geographical point of view, it is not a sea. This is the largest inland body of water on the planet, that is, the Caspian Sea is the largest lake on the planet.
But in recent years there has been a decrease in the area of the Caspian due to the fall of its level, and soon it may lose its title. Every year since 1996, there has been a decrease in the level of the reservoir by 6.7 centimeters. There are about 1 meter left to the historical minimum, which was recorded in 1977. The northern, Russian-Kazakhstan part of the lake, as the most shallow, suffers most from the drop in level. Also, the deltas of the Volga and the Urals are noticeably degrading, they are becoming shallow. This situation has a negative impact on the state of the Caspian Sea: the salinity of the reservoir increases, and the size of fish stocks decreases. The transport system of the region also bears losses: water recedes from port cities. According to experts, if the current rate of shallowing continues, by the end of the 21st century, the northern part of the reservoir may become dry land. And the Volga, in all likelihood, will flow into marshland.
The scientific teams of the countries located on the coasts of the sea, as well as international experts, are trying to find out the reason for this negative process. Although the water level in the Caspian Sea falls not for the first time. As it turned out, in the last 3 thousand years there have been regular fluctuations in sea level within 15 meters.
On the graph: fluctuations in the level of the Caspian Sea over the past 170 years According to scientists, the shallowing of the Caspian Sea is due to many factors. But the main reason for the fall in the level of the lake is considered to be climate warming in the Central Asian region, as well as in the Volga River basin - the main source of food for the Caspian Sea. According to experts, the average annual air temperature in the Caspian region has increased by 1 degree over the past 20 years. Due to the fact that the Caspian Sea-Lake has no connection with other seas and oceans, its level depends mainly on precipitation, water inflow with tributaries and on the amount of evaporation. Due to the increase in air temperature, the cost of water for evaporation increases, which, in terms of such a gigantic area, translates into significant losses. Today, the Caspian Sea has a negative water balance: more moisture evaporates from its surface than atmospheric precipitation, the Volga, the Urals and other tributaries bring.
But when analyzing long-term changes in the level of the lake, scientists revealed discrepancies between the magnitude of the runoff and the water level in the lake. That is, during the years of full-flowing tributaries, the sea level fell, while with a decrease in runoff, it even slightly increased. In this regard, another hypothesis was put forward for changing the level of the lake - a geological one. Scientists have suggested that the level of the lake is falling due to the movement of the earth's crust in the area of the reservoir. Shifts lead to an increase in the volume of the sea basin.
But whatever the reasons for the shallowing of the Caspian Sea, today the scientific world is busy developing measures to prevent this process. Various projects are being proposed to divert the flow of the northern rivers of the Russian Plain, to build a canal that will connect the Azov and Caspian Seas, and to build a dam that will separate the shallowing northern and deep-water southern parts. In the meantime, scientists, economists and politicians are choosing suitable options, the Caspian Sea continues to shallow. And such a situation could lead to the largest environmental disaster in the region in the foreseeable future.
Sinking cities Razumov Gennady Aleksandrovich
WHAT IS HAPPENING TO THE CASPIAN SEA?
The history of terrestrial civilization is only one millionth part of the total history of the development of the Earth as a planet. Therefore, modern humanity is in the geological time scale in the position of a newborn baby who has not yet learned to catch not only the change of seasons, but even the day. That is why we simply do not notice many natural processes related to climate and geology at all, and if we do, we often cannot explain.
Rice. 31. Water level fluctuations in the Caspian Sea
This fully applies to the problem of changes in the water level of the seas and oceans, including the Caspian Sea. The falls and rises of its level, which occurred "before the eyes" of mankind, are only a moment in the long life of the sea. Hence the nature of our perception of long-term fluctuations in sea level. Its peculiarity lies in the fact that we still cannot catch their patterns, and they seem to us random, spontaneous, stochastic, as mathematicians say. Even A. Einstein once jokingly said: “I just can’t believe that the Lord God is playing dice with us.” But this is how we are compelled to approach research related to the climate and hydrology of the ocean and land.
The stepped chart of the Caspian Sea levels is shown in fig. 31. Only the final part of it is confirmed by the buildings of man, the sunken cities, fortresses and temples described above. The main information was obtained by paleogeomorphological studies, i.e. the study of ancient sea terraces, which have preserved traces of the former standing of the sea level. The remains of marine fauna and flora buried under the layers of the earth, erosion of ancient coasts, deposits of sea pebbles and other evidence of the violent and everyday activity of sea waves make it possible to draw up a more or less detailed and reliable picture of the change in the water content of the Caspian Sea over hundreds and thousands of years of its existence.
Over the course of 100 thousand years, the Caspian Sea, repeating the fate of all drains and reservoirs of the northern hemisphere, experienced severe “hypertonic crises” four times, when the water level in it rose sharply in post-glacial periods. There was a transgression of the sea, it advanced on land, flooding vast spaces. Three times after this, the Caspian retreated back into its basin. By the way, there was a time when its dimensions were almost 13 times smaller than today.
Against the background of these large transgressions and regressions of the sea, there were also smaller fluctuations in the water content of the Caspian Sea. For 25 thousand years, about 15 phases of high and low sea level were noted with an average duration of each phase of about 170 years (from 40 to 380 years). Starting from the VIII millennium BC. the level of the Caspian Sea was 37.4 m below the level of the spring ocean, i.e. very close to its current level. However, this is an average. The maximum and minimum were respectively 23 and 32 m, thus the difference in levels was as much as 10 m, which corresponds to a change in the volume of water in the sea by 3.5 km 3 . Starting from 1809, there was a continuous general decrease in the water content of the Caspian. At first, the average decrease in the water level in it was 4.1 cm per year. But then, approximately from 1930, the level of the Caspian began to decline at a rate of 20 cm per year. This catastrophic decline in 1941 slowed down a little, but by 1956 the level of the Caspian was already 2.5 m lower than in 1929. For example, in the Baku region, the sea receded by more than 150 m. The channels of the Volga delta also became significantly shallower, and the bottom of the sea was exposed. In general, the sea water area has decreased by 40 thousand km2, i.e. to the area of the Aral Sea.
A variety of sectors of the national economy are associated with the position of the sea level: the oil and gas industry, fishing, shipping, agriculture, etc. Suffice it to say that the Caspian Sea provides almost 90% of the world's sturgeon catch to understand our excitement when the shallowing of river channels and backwaters led to a decrease in the area of spawning grounds. But the Caspian also provides a quarter of all fish catches in the inland waters of the USSR, and in general, almost a third of the country's total gross output is produced in its basin.
The first thing scientists noticed when they tried to explain the sharp drop in the level of the Caspian Sea was the intensive withdrawal of fresh water flow that feeds the sea, which began in the 1950s.
After all, it was during these years that the construction of large Volga reservoirs began (Kuibyshev, Volgograd, Saratov, etc.), which were filled by many floods of the Volga. At the same time, powerful water withdrawal for the needs of agriculture (irrigation) and industry began.
It must be said right away that the profound impact of human technogenic activity on global or at least regional natural processes is in many cases greatly exaggerated. This also applies to ideas about the impact of the irretrievable withdrawal of part of the runoff of the rivers that feed the Caspian Sea on lowering its level.
According to various estimates, irretrievable losses of freshwater runoff amount to 20–40 km3; are equal to almost 10% of the income item of the water balance of the Caspian Sea. Moreover, this value is not stable, but constantly growing. Thus, according to the Institute Hydroproject, the withdrawal of water runoff for economic needs from 1950 to 1960 increased by more than 2.5 times, and by 1970 the sea level should have fallen by at least 1.5 m due to human activities. By the way, this was the forecast given in 1950 and 1956. famous Soviet explorer of the Caspian Sea B.A. Apollo.
However, such a decrease in sea level did not occur. The Caspian Sea, however, continued to "lose weight", but at a much slower pace than in 1930-1940, and in 1978-1980. even a slight increase in the level began, which then reached a mark of 28.5 m. It is obvious that the role of the withdrawal of fresh water in the Caspian Sea basin is not so great. One of the explanations for this may be the rejection of the idea that we are talking about irretrievable losses of water flow. In fact, a significant part of the fresh water taken from the Caspian in the form of groundwater returns to it and, thus, is not lost to it.
For example, water taken from rivers and reservoirs for irrigation needs, almost 50-80% of which, when used in agricultural fields, filters into the soil and enters groundwater. After all, it is no secret that most of our irrigation and other canals have an efficiency of 0.3-0.5, i.e. up to 70% of all water seeps into the ground.
One way or another, but the decisive role in the catastrophic shallowing of the Caspian Sea was the withdrawal of water from the Volga and other rivers in 1940–1950. obviously couldn't play. So what?
The most widespread is the climate-meteorological hypothesis, which links the regime of sea levels with climate fluctuations. It proceeds from the general, almost undisputed position that after the separation of the Caspian Sea from the World Ocean, it fell completely into the power of regional and global atmospheric processes operating not only within the catchment area of the sea (and, of course, its water area), but also in other large areas adjacent to it.
The water balance of the Caspian Sea consists of the following components. Firstly, it is the surface river runoff, which plays the main role in maintaining the water content of the sea. The Volga, Ural, Kura, Sulak, Terek and other rivers bring about 300 km 3 of water to the Caspian Sea per year. Atmospheric precipitation gives a much smaller increase - a little more than 60 km 3, since this area is arid, arid. At the same time, a huge amount of water goes to evaporation from the surface of the sea, although its area is 10 times smaller than the drainage basin (about 3 million km 3). The Caspian Sea literally “throws into the wind” about 360 km 3 of water per year. If there were no replenishment of the water reserves of the Caspian Sea with fresh water, its level would fall by 1 m every year only due to evaporation. The most powerful evaporator, a real “boiler” that evaporates sea water, until very recently was the Kara-Bogaz-Gol Bay, which annually removed a layer of water 3 cm thick from the sea surface. After the blocking of the strait, which connected the bay with the sea, which took place in 1980, the Caspian received water "additives" in the amount of 10 km 3 per year. However, the overlap of Kara-Bogaz-Gol was not a very thoughtful decision. Its complete separation from the Caspian led to severe environmental consequences. That is why at present a lock-regulator has been built in the overlap dam, which to some extent restored the hydraulic connection of the bay with the sea. The Caspian Sea, "abandoned to the mercy of fate" by the World Ocean, behaves far from the way its "progenitor" does. During the period of warming, when glaciers began to melt, the level of the World Ocean quickly rose, while the Caspian behaved somewhat differently. At the end of the collapse of the ice sheets, the rate of rise in the level of the World Ocean slows down, at the same time, the level of the Caspian Sea begins to decline sharply. And during the period of glaciation, when the level of the World Ocean dropped significantly, the “golden” age began for the Caspian Sea. The so-called "pluvial" regime was established here, i.e. low air temperature, high humidity, and, consequently, low evaporation from the sea surface. In addition, about 120 km 3 of water per year was constantly supplied to the Caspian Sea basin by the huge Scandinavian ice sheet. Therefore, the level of the Caspian Sea, in contrast to the World Ocean, was intensively rising.
In the same way, in our time, many scientists associate the behavior of the Caspian Sea with the ongoing warming of the Earth's climate. As proof of this, the fact of the reduction in the areas of the Atlantic and Greenland glaciers is cited, which leads to a rise in the level of the World Ocean by an average of 1.2 mm per year. And since the Caspian Sea should behave in the opposite way, its water content decreases.
In the climatological hypothesis, everything seems strict and logical; almost all the facts known to us today fit into it. And yet there are doubts...
Let's take another look at the graph of fluctuations in the level of the Caspian Sea over the past decades (see Fig. 31). Isn't it falling too steeply in the period 1930-1940? After all, the rate of decline in the level in these years is completely incommensurable with the rate of climate warming in the northern hemisphere, which is slow and smooth. The thought involuntarily arises: is there some kind of high-speed impulsive force here? First of all, it may be the internal force of the Earth. It is with it that the supporters of the tectonic hypothesis associate sharp fluctuations in the level of the Caspian Sea.
Indeed, sea levels are very sensitive to changes in the capacitive characteristics of the sea. Even the smallest changes in the volume of the Caspian Sea Basin should immediately be reflected in the position of the sea surface. Geological and geographical studies carried out in recent years on the territory of southwestern Turkmenistan and partly within Azerbaijan and Georgia have shown that in the Caspian region there is a constant subsidence of the earth's surface. The tectonic trough of the southern part of the Caspian Basin can lead to its deepening and the flow of water into it from other parts of the sea.
By the way, it is quite possible that the reports that seem now doubtful about the periodic connection of the Caspian Sea with the Sea of Azov in historical time through the Manych Strait could really take place. Vertical fluctuations of the Earth's surface in the area of the Kuma-Manych Isthmus could lead to periodic flooding or shallowing of the strait.
So, three hypotheses, three opinions. Which one is the most correct? Obviously, orthodox adherence to one of them would be a mistake. Apparently, in the area of the Caspian Basin, all three factors are active, leading to fluctuations in sea level. Climate change is long term. Periodic tectonic changes superimpose on them, as on a general background - troughs of the seabed and, perhaps, to some extent, artificial selection of fresh water from the rivers that feed the Caspian Sea.
If we have difficulty explaining the past, then we are even more unable to reliably predict the future. Long-term forecasts of the regime of water levels in the Caspian Sea are also doubtful, as are predictions of climate and seismic activity of the Earth for remote periods of time.
After all, to answer the question of how the level of the Caspian is changing, you need to know a lot. For example, according to S.V. Varushchenko (Moscow State University), for such a forecast it is necessary to clearly understand in what direction the climatic situation will develop not only within the Caspian basin, but throughout Europe, North Africa and the Atlantic Ocean. Thus, it is necessary to predict how the cyclones emerging over the Atlantic will behave, how active and saturated they are, where they will go and where they will stop. So far, we cannot foresee this.
Since the last century, various projects have been proposed to save the Caspian Sea from shallowing. All of them can be divided into two groups. One of them relates to the expenditure item of the sea water balance and to the problem of reducing the amount of evaporation from the sea surface. The other, on the contrary, is based on the incoming part of the balance and the need to increase the amount of water flow into the sea.
One of the most famous projects of the first group is the proposal of B.A. Apollos to cut off the northern part of the Caspian Sea with an earthen dam and create a freshwater reservoir in it. Water from the North Caspian reservoir will thus not go into the deep southern part, the area of which, due to evaporation and a decrease in inflow, will gradually decrease, exposing the oil-bearing areas of the seabed. This plan did not take into account the possible serious violation of the ecological balance of the area. In particular, a violation of the current degree of salinity of the sea can lead to a change in the flora and fauna of the sea, the disappearance of valuable species of semi-anadromous fish.
In 1879, the Russian engineer M. Danilov proposed to artificially restore the connection between the Caspian Sea and the World Ocean through the Manych Strait. In our century, these plans have found concrete expression in the construction project of the Manych Sea Canal. At the same time, two options for the route were considered: from the Black Sea (with the beginning near Novorossiysk) and from the Azov Sea (from the mouth of the Don). Water should flow by gravity into the Caspian Sea and maintain its level at a given level.
The main doubt in this project is the violation of the ecological balance of the area. The supply of highly mineralized sea water from the Black Sea (according to the 1st version of the canal route) would seriously change the hydrochemical regime of the northern Caspian. The supply of fresher waters from the Sea of Azov (according to the 2nd option) is not advisable due to the danger of its salinization.
In the last 10 years, there has been a struggle over the project of transferring part of the flow of the northern rivers to the Caspian Sea basin. According to him, water was to be supplied to the Volga and the Caspian from the rivers Sukhona and Pechora. It envisaged the construction of large water intake hydroelectric facilities, which would make it possible to select and direct to the south, first 20, and then 40 and even 60 km? water. Such assistance to the Caspian should have been very tangible. But, most importantly, numerous water consumers, now supplied from the Volga and having an extremely tight water supply regime, also had to receive additional food.
However, in our time, any plans to "correct" the mistakes of nature have to be treated very carefully. Like any other human impact on the environment, the transfer of river flow from one basin to another can have the most serious consequences.
Some of them are visible immediately, and therefore it is not so difficult to take into account and prevent them. Others can be predicted in advance, but it is rather difficult to assess how and to what extent they will manifest themselves in the future. But the third, the most unpleasant, are those that cannot be foreseen now. They are invisible, secretive and can appear so unexpectedly that their elimination will be impossible.
The first, most obvious negative consequence of the transfer of river flow to the south, which immediately comes to mind: is this not the same thing that the unlucky tailor from the fable of I.A. did? Krylova Trishka, who cut off the skirts of the suit to lengthen the sleeves? Are we trying to patch "Trishkin's caftan". By flooding the arid South at someone else's expense, are we impoverishing the North? Will water famine come to the northern regions as well?
And the next question, connected with the danger of shallowing of the small rivers of the North, with the overdrying of the tundra, with the disappearance of marsh forms of vegetation. When water is withdrawn from rivers and lakes, their level will decrease, which will also lead to a decrease in the level of groundwater, which, in turn, feeds numerous rivers, streams, barrels, swamps. Therefore, general dehydration of soils, destruction of peatlands can begin. Pastures for deer will disappear, the number of valuable and rare species of fish and birds will die.
Usually, supporters of regional and global projects for the reconstruction of the country's water management answer these questions in the following way. The implementation of individual projects for the transfer of river flow should ultimately lead to the creation of something like the "Unified Water System" first of the European part of the USSR, then of the entire Union. Then, through numerous canals and rivers connecting almost all river basins, it will be possible at any time to transfer water supplies from one region of the country to another, from north to south, from east to west, and vice versa. Therefore, if it turns out that somewhere in the north there is a shortage of water, it will be possible to give it back. And thus the balance will be restored.”
But water is not electricity, and its distillation back and forth along rivers and anti-rivers flowing backwards will inevitably again affect the natural conditions of river and lake channels and shores that have developed over thousands of years, on bottom and coastal vegetation, on fish stocks and much more.
Changes in the ecology of the Arctic Ocean are among the consequences of the diversion of the flow of northern rivers to the south, which are difficult to quantify. After all, a decrease in the inflow of river waters is at the same time a decrease in the heat flow into the ocean. Will this lead to a violation of the existing heat balance, a change in the thermal regime of the coastal part of the ocean, and, as a result, to the arrival of a new, artificially created fifth ice age? There is no exact answer to this question yet.
Now a few words about the consequences of such transfers, which cannot even be predicted. Unfortunately, nothing can be said about them. I can only, perhaps, give one example, which we all have before our eyes.
In the postwar years, the USSR urgently needed to raise the economy, restore industry, and improve agriculture. The basis of this rise was (is it true?) the development of hydropower. In an unprecedentedly short time, hydropower giants with large reservoirs on the Volga, Dnieper, Don and other rivers rose. Man-made seas spread on the planes of the East European Plain flooded large areas. This consequence of the construction of the hydroelectric power station was obvious.
But at that time, experts did not take into account that 10, 15 and 20 years would pass, and the area of reservoirs would grow and grow. The waves will wash away the slopes, bring down the earth into the water, the coastline will creep further and further, devouring tens of thousands of hectares of usable territory. And this process never stops.
The same happens with the groundwater level, which rises simultaneously with the water level in the reservoir. After the formation of reservoirs on the banks of the lowland rivers, a real underground flood began, which has not stopped to this day. The swamping of low-lying lands is intensively going on, many cities, towns and industrial enterprises are flooded. We have to take serious measures to protect a number of large cities from flooding.
There are many such examples when the calculations of engineers are difficult to predict. For all these reasons and under public pressure! about the opinions of the work on the project of diversion of the northern rivers in 1986 were terminated.
But the most surprising thing is that he began to solve the problem of the shallowing of the Caspian Sea himself, without human intervention. The fact is that in the second half of the 1970s, the sea level drop went at a much slower pace than in the 1930s and 1940s, then it stopped, and from 1978 even an increase in the level suddenly began, which continues to this day. By 1985, the water level in the Caspian Sea had risen by 80 cm and flooded the coastal strip of the beach by 50 m. In subsequent years, this rise did not stop. What's the matter? What is it, a new transgression of the sea or one of those small random uplifts that have repeatedly occurred over the past decades? Only time can give an accurate answer to this question.
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Scientists conducted a study of the state of the Caspian Sea, and came to disappointing conclusions. According to their forecasts, at the current rate of global warming, the Russian part of the water area may disappear in the coming decades.
Russian and French scientists have come to the conclusion that the Caspian Sea may disappear in 75 years, according to the journal Geophysical Research Letters. Experts analyzed the water level in the water area and came to the conclusion that in the period from 1996 to 2015 it decreased by seven centimeters annually.
ON THIS TOPIC
In total, during this time, the sea "drained" by 1.4 meters. This is a meter higher than the historical minimum, which was recorded in the late 70s. Scientists believe that this figure will only worsen over time. Moreover, the northern part of the sea, which is located on the territory of Russia and Kazakhstan, will suffer the most.
According to experts, the main reason for the shallowing of the sea is global warming. So, over the past 30 years, the water temperature of the surface layer of the atmosphere has increased by one degree.
Earlier, some experts announced the threat of the disappearance of Lake Baikal. The reason for this may be the construction of a hydroelectric power station on the Selenga River in Mongolia.
According to the forecasts of a number of experts, already in the process of construction, the quality of water and its temperature will change, and additional greenhouse gases will also begin to be released. The HPP will negatively affect the migration of animals and fish, and will also lead to an increase in seismic and epidemiological danger in the region.
