The character of the atmospheric general circulation during summer-season droughts over Eastern Europe/Western Russia and North America during the late twentieth and early twenty first century is examined here. A criterion to examine atmospheric drought events that encompassed the summer season (an important part of the growing season) was used to determine which years were driest, using precipitation, evaporation, and areal coverage. The relationship between drought and the character of the atmosphere, using the Dzerzeevsky weather and climatic classification scheme, atmospheric blocking, teleconnections, and information entropy, was used to study the atmospheric dynamics. The National Centers for Environmental Prediction (NCEP) re-analyses dataset archived at the National Center for Atmospheric Research (NCAR) in Boulder, CO, USA, is used to examine the synoptic character and calculate the dynamic quantities for these dry events. The results demonstrate that extreme droughts over North America are associated with a long warm and dry period of weather and the development of a moderate ridge over the Central USA driven by surface processes. These were more common in the late 20th century. Extreme droughts over Eastern Europe and Western Russia are driven by the occurrence of prolonged blocking episodes, as well as surface processes, and have become more common during the 21st century.

This study analyses long‐term changes in drought indices (Standardised Precipitation Index—SPI, Standardised Precipitation–Evapotranspiration Index—SPEI) at 1 and 3 months scales at 182 stations in 11 central and eastern European countries during 1949–2018. For comparative purposes, the necessary atmospheric evaporative demand (AED) to obtain SPEI was calculated using two methods, Hargreaves‐Samani (SPEIH) and Penman‐Monteith (SPEIP). The results show some relevant changes and tendencies in the drought indices. Statistically significant increase in SPI and SPEI during the cold season (November–March), reflecting precipitation increase, was found in the northern part of the study region, in Estonia, Latvia, Lithuania, northern Belarus and northern Poland. In the rest of study domain, a weak and mostly insignificant decrease prevailed in winter. Summer season (June–August) is characterized by changes in the opposite sign. An increase was observed in the north, while a clear decrease in SPEI, reflecting a drying trend, was typical for the southern regions: the Czech Republic, Slovakia, Hungary, Romania, Moldova and southern Poland. A general drying tendency revealed also in April, which was statistically significant over a wide area in the Czech Republic and Poland. Increasing trends in SPI and SPEI for September and October were detected in Romania, Moldova and Hungary. The use of SPEI instead of SPI generally enhances drying trends.

The features of regional atmosphere circulation, which are accompanied simultaneously by two high impact hydrometeorological phenomena (such as droughts and dry winds) in the Black Sea Steppe zone of Ukraine were considered. Dry wind as a complex phenomenon is widespread throughout Ukraine during the warm season of the year. Dry winds often accompany a drought, but they appear as peripheral processes in contrast to the droughts, which are usually formed in the central parts of anticyclones. The number of days with dry winds at the Steppe stations varies on average from 10 to 20 cases to 40-50 cases per warm season, while in the coastal zone the number of days decreases sharply due to a common increase of air atmospheric relative humidity. Analysis of the interannual dynamics of dry winds showed that the number of days with dry winds increases significantly in seasons characterized by a high aridity, according to values of the drought index used. Two time intervals with high and low frequency of seasonal droughts and dry winds were detected during the considered period: 1995-2015. These phenomena have become more intense after 2004, compared to the previous decade. Backward trajectories of air particles showed that the most cases of dry winds originate in air masses, which form up to 5 days previously at the surface level to the east or north-east outside of the territory of Ukraine and then pass into the study area within 5 days.

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Monthly precipitation and the 3-month Standardized Precipitation Index (SPI) were used to reveal the patterns of rainfall and severe drought frequency over the East European Plain in the period 1953–2011 in the opposite phases of the quasibiennial oscillation (QBO). Differences of precipitation and severe drought frequency in May and in June in the westward and eastward phases of the QBO phases are explained by circulation variations. The analysis indicates less frequent severe drought events over Ukraine and at the center of the European part of Russia in May in the westward QBO phase due to the intensification of the storm track over the East European Plain. The weather conditions in May and in June in the years of the westward QBO phase were more favorable for the yield. The difference of spring wheat yield in the westward and eastward QBO phase exceeds the same difference of winter wheat yield in the Central Black Earth region and in the south regions. Ukraine and the region to the east of the Sea of Azov are the most vulnerable areas of increased risk of severe drought during the active growing season at the end of the 20th and beginning of the 21st century.