Hydrometeorological hazards during the winter periods in the Northern Caspian and dynamics under the influence of climatic changes

Abstract

Hydrometeorological hazards of the Northern Caspian during the winter periods 1950–2020—due to climatic changes were investigated. Hydrometeorological hazards for the period 1950–2020 are considered: severe winter periods, early ice freeze-up, storm waves, wind surge, as well as cumulative hydrometeorological hazards—combinations of storm waves and surge. Geographic information system (GIS) “Ice regime of the southern seas of Russia” is the information basis for the study of the ice regime of the Caspian Sea. Storm activity in the Caspian Sea were reconstructed using SWAN spectral wave model. Based on the cumulative freezing-degree days winters were divided by severity—mild, moderate and severe. During the study period, moderate types of winters prevail (59.4 %), and the number of severe and mild winters is the same and amounts to 14 pcs. (20.3 %) of each type. Due to climate change, the number of mild winters is increasing, and the number of severe ones is decreasing. Since 1985, 3 severe winters (2002/03, 2007/08, 2011/12) have been recorded. As a result, the ice cover area decreased by ∼7–10 %, and the duration of the ice season at the observation point Peshnoy was reduced by 5 days. 157 situations of combinations of storm surge and storm waves are identified: 140 are cases of potential situations of cumulative phenomena of a combination of storm and surge phenomena with a speed of 15 m/s or more of winds of effective directions. The largest number of cases of cumulative dangerous hydrometeorological hazards with a wind speed of more than 15 m/s is observed in March. After the 2000s there was an increase in the number of cases and duration of dangerous hydrometeorological hazards in November and March. A direct relationship between the number of cases of cumulative dangerous hydrometeorological hazards and the severity of winters has not been found.