Characteristics of Spring–Summer Drought in Dry and Wet Periods in the South of European Russia

Abstract

The distribution pattern of the characteristics of spring–summer droughts during periods of increased and decreased annual wetting in 12 administrative entities of the south of European Russia in 1901–2018 are studied. During this time, four periods of different humidification conditions (alternating wetter, dry, wet and again dry periods) of different durations are well traced according to anomalies in the aridity index in seven regions: Kursk, Belgorod, Voronezh, Saratov, Volgograd, and Rostov oblasts and the Republic of Kalmykia. A desiccation period was noted in Samara and Astrakhan oblasts from the beginning to the middle of the 20th century. The desiccation period then gave way to a wetter one. The most frequent change of periods with different moisture conditions was observed in Stavropol krai, where five alternating periods were identified. It has been established that the frequency of spring–summer droughts is consistent with the long-term humidification conditions. According to the standardized precipitation index, it increases on average by 1.5 times in the dry period with a slight increase in drought intensity. The conditions of increased humidification observed in all of the examined administrative subjects in the second half of the 20th century were replaced by drier conditions at the beginning of the 21st century. The spread of more arid conditions began in the eastern oblasts. The development of the dry period in the 21st century is confirmed by the distribution of the NDVI vegetation index in the negative trend. In the absence of statistically significant aridization trends for more than a century, all of the considered oblasts of the south of European Russia undergo long, intracentury periods of aridization strengthening and weakening, which are characterized by significant differences in the frequency and intensity of spring–summer droughts.