Study of the surface temperature of the Caspian Sea according to MERRA-2 reanalysis data for the period 1980-2021

According to the data collected from MERRA-2 reanalysis for 1980-2021, using different statistical methods, the changes of the sea surface temperature in the Northern, Middle and Southern Caspian Sea, the reasons of their occurrence were studied, and the corresponding linear trends were estimated. It was found out that the average annual surface temperature in the period 2001-2021 increased by 0.5 in the Northern Caspian, by 0.9 in the Middle Caspian and by 0.7 in the Southern Caspian compared with the period of 1980-2000. Different trends in surface temperature in different months and seasons have been revealed under the conditions of global warming and lowering of the level of the Caspian Sea in different parts of the water area. In 1980-2021 there is a significant negative trend in surface temperature in winter in the Northern Caspian Sea, but in other seasons, a positive trend is observed throughout the sea. All trends, except for autumn in the Northern Caspian Sea, were statistically significant at 0.05 level, and in most cases even at 0.01 level. Increase of contrasts between winter and spring surface temperatures in the Northern Caspian Sea against the background of sea level fall can extremely negatively affect the ecological state, including the biodiversity of the sea.