Projected distribution of the warm season droughts over the territory of Ukraine in 2021-2050

Abstract

Introduction. Drought is a natural phenomenon that occurs in all climates, and is one of the most relevant natural hazards, which propagates through the full hydrological cycle and affects large areas, often with long-term economic and environmental impacts. A prolonged deficit in precipitation over a defined region cause a meteorological drought, while the other types of drought describe secondary effects on specific ecological and economic compartments. Recent trends in the drought distribution and intensity shows that Europe splits into two big areas, in which the southern and western regions have positive trends of drought frequency, duration, and severity, and the northern and eastern regions show a decrease in this parameters. Regarding the long events, territory of Ukraine belongs to the areas in which a prominent decrease in drought frequency, duration and severity are fixed. But positive trends in the drought characteristics are observed on the Black Sea coast, also in the Carpathian region, many droughts occurred in the past three decades. The purpose of this study to examine the results of analysis of the spatiotemporal distribution of warm season droughts (April-October) across the administrative areas of Ukraine in 2021-2050 under the climate scenarios RCP4.5 and RCP6.0 with them comparing. Data and methods. Drought estimation was performed using the SPEI index (the Standardized Precipitation Evapotranspiration index). The inclusion of temperature through the potential evapotranspiration (PET) along with precipitation data allows SPEI to account for the impact of temperature regime on a drought situation. A drought episode for given time scale is defined as a period, in which SPEI is continuously negative and reaches a value of –1.0 or less. In this study, the gridded fields of monthly air temperature and precipitation intensity from multimodel sets of global CMP5 models are taken for calculations of SPEI. Data access was made through the Climate Explorer. All data were averaged over the area of each of 25 administrative regions of Ukraine. Research results. Analysis of the time series of the calculated SPEI index for both scenarios showed that in all regions of Ukraine there will be a tendency to transition from moderately wet conditions in 2021-2035 to droughty conditions in 2037-2050. In the first half of the study period drought is expected near 2024, as well as in 2030-2033 almost in all provinces except southern areas. In the second half of the period prolonged seasonal drought is projected in 2044-2047 over all Ukraine and in some areas drought may reach an extreme intensity. Decade analysis of the SPEI7 time series showed that in both scenarios in all regions of Ukraine, the least number of dry seasons is expected from 2021 to 2030. The highest number of dry seasons in this period may reach up to 4-5 cases per 10 years in the western regions under RCP6.0 scenario. In other regions the number of dry warm seasons will be 2-3 cases per 10 years. In the period from 2031 to 2040, the number of dry seasons will increase substantially in all regions of Ukraine under RCP4.5 scenario, in which their number will be 5-6 cases per 10 years. Under RCP6.0 scenario, an increase in the number of droughts will be observed in all areas except the western regions, where will be from 2 to 4 dry seasons per 10 years. In the last decade from 2041 to 2050, in both scenarios, the number of dry seasons will increase throughout Ukraine compared to the previous decade. Under RCP6.0 scenario, the greatest increase is projected in the north of the country and in some other regions throughout Ukraine, where the maximum number of seasons with droughts will reached up 8-10 cases per 10 years. Conclusions. Comparison of the SPEI7 time series for both scenarios showed that under RCP6.0 scenario the transition from wet conditions to dry conditions is projected during long period from 2030 to the early 2040s. In this time, small interannual variations of the SPEI index across all regions are expected, and only in the last decade the dry seasons will prevail. In addition, in the RCP6.0 scenario, maxima of drought frequency are expected in few different regions of the country, compared with the RCP4.5 scenario, which indicates significant scenarios' differences in the predicted state of the regional atmospheric circulation determined the temperature and precipitation regimes in the future.