## 3 Results and Discussion
### The Problem of the Caspian Sea Level Decline
In accordance with the forecast of Roshydromet (Russian Hydrometeorological Survey) in 2015, the level is expected to decrease by 20... 30 cm. As the researchers note, the probability that the lake level will continue to decrease in the coming years is very high [105]. According to [106] river runoff and evaporation have the biggest impact on long-term fluctuations of the Caspian Sea level. Moreover, it is known that the flow of the Volga River accounts for 80% of the total volume of river inflow into the Caspian Sea. And due to evaporation, the Caspian Sea level decreases by average of 97 cm per year. For the long term prospective, the role of these factors was assessed by the authors according to certain scenarios of climate change and water consumption in the basin. The calculated results for the Representative Concentration Paths (Scenarios for the evolution of anthropogenic greenhouse gas emissions into the atmosphere in the future) RCP 4.5 and RCP 8.5 scenarios showed that the inflow of water into the Caspian Sea has no expressed trend. Calculations of precipitation and evaporation have shown stable trends, from which it follows that evaporation from the Caspian Sea surface area will increase as a result of the prospected increase in air temperature. The inflowing part of the water balance of the Caspian Sea will not have serious changes, and the \"outflow part\" evaporation will increase, which can affect the decrease of the Caspian Sea level and the reduction of its water area. Figure 18: Long-term fluctuations of the Caspian Sea level [104]. According to [PERSON] et al. [107], during the current decrease of the Caspian Sea level (2006... 2019), the average inflow into the Caspian Sea decreased by 7.5% relative to its average long-term value, the least precipitation amount was in the area of the Caspian Sea, and evaporation processes were more intensive, moreover, due to the series of dry years in the Volga River basin. The main reason for this low water period is climate warming, which has spread throughout the entire northern hemisphere [108]. The authors come to the conclusion that the level fluctuations of the Caspian Sea are mainly due to the ratio of the characteristics of the water balance, which are changing under the influence of anthropogenic climate change. [PERSON] [109] has presented a forecast of Caspian Sea level changes for the near future. According to the author's calculations, and according to their first version (the first period), the lake level in 2020 should reach the mark of--26.85 m b.s.l, and in 2030--27.10 m b.s.l. According to the second version of the calculation, the level of the Caspian Sea in 2020 will be at the level of--27.05 m b.s.l, and 2030 of--27.85 m b.s.l. Therefore, by 2030, the lake level for the first option will be at the level registered in 2010, and for the second it will reach approximately the level of 1993, i.e., it will fall by 75 cm. According to the data received from the National Hydrometeorological Organizations of the Caspian littoral states [110], the mean level of the Caspian Sea in 2019 decreased by about 17 cm as compared to 2018 (\(-\)28.03 m b.s.l) and amounted to \(-\)28.20 m b.s.l. According to [PERSON] and [PERSON] [107] the average level of the Caspian Sea in 2020 was 28.3 mb.s.l. Comparing these real measured data with the forecast data of [PERSON] [109] can be mentioned that the Caspian Sea level decreased more as forcasted. It should be noted that against the background of high anthropogenic contamination of the north-eastern part of the Caspian Sea, the intensive dropping down of the water level in this shallow zone, will cause a further deterioration of the environmental conditions of this water area with serious consequences for nearly all species habitats. Under such conditions of a decreasing water mass, the concentration of various toxic compounds increases sharply. This may be the cause of mass death of fish, seals and other aquatic organisms in this zone.