Spatiotemporal Distribution of Soil Moisture Content over Ukraine and Its Relationship to Atmospheric Conditions

Spatiotemporal distribution has been assessed using time series of the monthly area-averaged soil moisture content of 0-10 cm underground, generated by NASA GLDAS_NOAH025_M model (Giovanni online data system), for period 2000-2019. Calculated Soil Moisture Anomaly Index (SMAI) was used to characterize the degree of saturation of the soil, comparing to normal conditions.

The clear annual soil moisture content (SM) course is observed in all agroclimatic zones of Ukraine, when the maximum is observed in February, and the minimum is in August or September. The lowest SM values are fixed in the Western Steppe and the maximum in the Carpathian region and Polesie. The analysis of time series of the SMAI showed that during the study period in summer and autumn months there was a tendency to reduce the interannual amplitude of index fluctuations and observed the transition from mostly positive values to negative ones. In winter and spring, no significant trends were found in the SMAI values.

Analysis of the correlation coefficients between the SMAI and the North Atlantic Oscillation index (NAO) showed that the statistical relationship is weak, but in some months it is significant. For all regions, except the Eastern Steppe, significant correlation coefficients are observed in March and May (-0.45 ...-0.77). The inverse statistical relationship indicates that under increasing zonal flow (NAO> 0), the SM in Ukranian areas decreases and contrariwise.

Analysis of the correlation coefficients between the SMAI and the blocking index ECBI showed that significant statistic relationship is observed in July and autumn. In July, a direct correlation was found, i.e. blocking of the zonal flow (ECBI>0) leads to an increase the SM. In October and November, negative correlation is fixed (-0.69 ...-0.49), i.e. blocking processes lead to decrease of the SM due to prevailing anticyclonic circulation in Eastern Europe this season.