Changes in Soil Drought Characteristics in European Russia According to In-situ and Satellite Data

Changes in the frequency, intensity, and duration of severe soil droughts in the upper soil layers in May and June in the European part of Russia (EPR) south of 55° N in the period 1981–2020 were studied based on soil moisture observations in the arable layer at 19 hydrometeorological stations, as well as in a 10-cm-deep layer according to the GLEAM model using satellite measurements. A close relationship was revealed between soil moisture in May–June according to satellite data and atmospheric moistening in April–June. The analysis of the results obtained indicates an increase in the frequency of droughts in the surface soil layer, caused by extremely low moisture, at the beginning of the growing season in most of the area studied in the first twenty years of the 21st century compared to the previous twenty years. Moreover, the largest statistically significant increase in the frequency of droughts by four events in May–June was observed in the Central Black Earth Region, the Volga Region, the Trans-Volga Region, the Azov Region, and the Black Sea coast. The increase in the frequency of droughts occurred against the background of the most noticeable decrease in moisture in the surface soil layer in the period 2001–2010. At the same time, the increase in the duration of such droughts in the same regions was the greatest and ranged from 15 to 30 days. The increase in the frequency of droughts in the Volga and Trans-Volga regions was accompanied by a significant decrease in soil moisture, the greatest in the study area. It was found that the majority of the most severe extensive droughts in the surface soil layer in May and June have been observed since the beginning of the current century. Differences in the frequency of soil droughts in the arable layer based on in-situ data were shown depending on the chosen definition.