Inna Semenova

This study analyses dry‐hot winds, or sukhoviys , a recurrent phenomenon during the warm season across most regions of Ukraine. Sukhoviys promote rapid moisture loss from soil and vegetation, inducing acute stress on crops and intensifying drought effects during critical growth periods. Defining a sukhoviy as an event characterised by air temperature ≥ 25°C, relative humidity ≤ 30% and wind speed ≥ 5 m s ⁻¹ , we identified sukhoviy events over the period 1973–2025 using observational data from 34 meteorological stations. Using the Sukhoviy Station Index (SSI), we assessed the activity of sukhoviy events across Ukraine, taking into account their meteorological characteristics and frequency of occurrence. Based on a compiled catalogue of sukhoviy episodes and the Sukhoviy‐Day Index (SDI), the most intense events were identified with respect to duration and spatial extent. The largest number of sukhoviy days occurs in summer, particularly in July–August, averaging 3–4 days per month, with temperatures of 30°C–32°C or higher. Short episodes lasting 1–2 days are the most common, accounting for 67% of all cases. Prolonged episodes of 10 days or more represent approximately 3% of events; nevertheless, such episodes may simultaneously affect up to 16–19 stations. At several stations, an increase in sukhoviy days with temperatures above 30°C has been detected since 2007. Analysis of atmospheric circulation conditions shows a predominance of types associated with easterly air‐mass advection, with sukhoviys also frequently observed during southerly advection and the eastward extension of anticyclonic ridges from the west.

The territory of Ukraine is highly vulnerable to dry phenomena due to its temperate continental location, extensive agricultural lands, and increasing climate variability. Of particular concern are rapidly developing droughts or flash droughts and intense dry-hot winds, both capable of causing severe crop damage.The occurrence and evolution of flash droughts during the warm season (April–October) of 1980–2024 were analysed using the Standardized Evapotranspiration Deficit Index (SEDI) based on actual and potential evaporation data from the GLEAM project. Flash droughts were identified using SEDI at the 4-week time scale, while daily-scale SEDI values were applied for analysis with dry-hot wind events. Dry-hot winds (known in Ukraine as “sukhovey”) were identified from observation records at 34 stations using threshold criteria of air temperature, relative humidity, and wind speed adopted by the National Hydrometeorological Service of Ukraine.The highest number of flash drought episodes (up to 30–35 events) was recorded in western and northern Ukraine. Positive trends in drought occurrence prevailed across most regions, especially in the southwest, centre, and north, whereas negative trends were found in the west and parts of eastern Ukraine. Flash droughts in western regions were generally short-lived (2–3 weeks), while the longest events (6–8 weeks) occurred in southwestern and central Ukraine. Most flash drought episodes were highly intense, frequently reaching extreme drought conditions (SEDI < −2.0), although their intensity showed a general decreasing trend during the study period.Five major flash drought episodes affecting at least 20% of Ukraine were identified during 1980–2024, lasting from 3 to 7 weeks. In most cases, dry-hot winds developed after drought onset, with their frequency increasing toward the middle of drought episode. Under dry conditions, dry-hot winds were associated with increased SEDI values, indicating temporary weakening of drought intensity. Thus, dry-hot winds do not initiate flash droughts but may influence their spatial development through changes in intensity.

Wildfires are an important part and natural process of most terrestrial ecosystems. Fire weather is one of the most important factors influencing fire activity and is largely determined by regional atmospheric circulation. An analysis covering the period from 2001 to 2021 showed that in Ukraine, fire activity follows a clear seasonal pattern, peaking in August and an additional peak in early spring. The largest burned areas are concentrated in the southern steppe regions of Ukraine, while the highest hot spots number is recorded in the northern half of the country, in the forest-steppe and mixed forests. The application of the Jenkinson–Collison classification to classify synoptic processes over Ukraine showed that the most frequent circulation types were associated with westerly advection, accounting for a total of 35%. Westerly flows dominated throughout the year; about 40% of circulation types with advection from the north and northeast occurred in summer, while more than 30% of southerly flows were observed in winter. One-third of all anticyclones occurred in autumn, and a similar proportion of cyclones was recorded in spring. No significant trends were found in either fire activity or the frequency of circulation types during the study period. The analysis of relationship between circulation types and fire activity showed that about 50% of annual fire occurrences (hotspots number) are associated with three circulation types, two of which are linked to advection from the west and east. The third significant contributor to fire occurrence is relatively rare anticyclones, while in different seasons the contribution of other circulation types may also increase. Analysis of two selected periods of high fire activity, in 2008 and 2020, revealed significant positive anomalies in the frequency of circulation types associated with the highest number of hotspots.

River floods in the mountainous regions of the Ukrainian Carpathians are a natural hazard that often leads to significant destruction and substantial economic damage to the region. The key driver of flooding is typically heavy rainfall, which results from certain patterns in regional atmospheric circulation. We studied the atmospheric circulation regimes over Ukraine for the period 1948–2021 using the modified Jenkinson–Collison classification. Circulation types associated with airflows from the western quarter are the most frequent throughout the year. However, seasonality in circulation patterns related to the dynamics of regional atmospheric centers of action is also well expressed. The linear trends in the frequency of circulation types are found statistically significant for meridional processes associated with advection from the north or south. Circulation types according to the Jenkinson–Collison classification, as well as the Niedźwiedź regional synoptic classification, were applied to cases of extreme floods in the river basins of the Ukrainian Carpathians to identify features of the pressure field leading to the formation of heavy precipitation. During the study period, 10 flood events, characterized by extremely high or historically significant water levels, were selected. Both pluvial floods in summer and mixed floods in winter were considered. In cases of the warm period, the circulation types with airflows directed towards the mountain range from the east or north are observed, and floods formed in the Ciscarpathia. In the cold period, circulation types with airflows from the western quarter increased precipitation and river discharge in Transcarpathia. 45% of observed circulation types belonged to the cyclonic group; however, the relative position of baric systems in other types also ensured the convergence of atmospheric moisture into the flood area.

Wildfires are natural disasters that impact ecosystems and economies many countries around the world. In Ukraine, wildfires occur in all agroclimatic zones, from steppes and forest-steppes to mixed forests. The country belongs to the regions in Europe experiencing the most significant increase in average annual temperature in recent decades, while precipitation levels remain unchanged, leading to soil drying due to increased atmospheric evaporative demand (AED) and more frequent droughts. The purpose of this study is to define the dynamics of ignition in Ukraine from 2001 to 2020 and to assess the relationship of their number with wet and dry conditions during the warm season. For the analysis, the MODIS active fire/hotspot database from the FIRMS (NASA) archive was used. Assessment of wet and dry conditions was conducted using the drought index SPEI on a 3-month time scale. Dynamics of both parameters were examined for regional time series tailored for the territory of Ukraine. Time course of the annual number of hotspots (HSN) showed strong interannual variability with two maximums during the study period: in 2008 and 2014-2015. A non-significant decrease trend in HSN was observed. In the seasonal distribution, two maximums of HSN were identified: a primary one in August and a secondary one in April. The number of ignitions increases rapidly in spring from March to April, but there is a sharp decrease in May, remaining low in June. In July, the number of ignitions increases, reaching a maximum in August, followed by a sharp decrease in September-October. In November and winter, the number of active fires is very low. Correlation analysis between HSN and SPEI showed that in spring, the closest relationship is observed with SPEI taken in April (r = -0.48), indicating that drier conditions in late winter and early spring contribute to ignition. In summer, the significant positive correlation is observed with SPEI taken May (r = 0.51), indicating that a wet spring apparently leads to the accumulation of more vegetation fuels. In autumn, wet-dry conditions of the previous summer months do not have a statistically significant relationship with HSN. In general, preceding drought may increase the number and areas of fires, however further research is needed to establish consecutive relationships between these compound phenomena. Keywords: wildfire, drought, SPEI, hotspot

The purpose of this research is to identify changes in the spatiotemporal distribution and severity of meteorological droughts in Ukraine between 1946 and 2020. In order to determine the role of precipitation and atmospheric evaporative demand on drought severity, two drought indices were applied for comparative analysis: the standardized precipitation index (SPI) and the standardized evaporation precipitation index (SPEI). Both indices were calculated on 3‐ and 12‐month timescales. The gridded dataset of monthly air temperature and atmospheric precipitation for Ukraine with high spatial resolution (0.1° × 0.1°), developed in the Ukrainian Hydrometeorological Institute, was used. Results of time series analysis of drought indices showed at least 20 episodes, in which more than 25% of the territory of Ukraine was affected by drought of varying intensity. Trends show an increase in drought severity determined mostly by a strong observed increase in the atmospheric evaporative demand. Tendencies towards an increase in the duration and intensity of droughts were observed mainly in the southwestern, central and northern regions of Ukraine. The main cause of the increase was droughts in spring and summer. The temporal analysis of the spatial distribution of areas affected by drought during the identified main drought episodes showed different patterns in drought propagation across the territory of Ukraine.

The summer of 2022 was very dry across Missouri and the surrounding regions including much of the Great Lakes, Midwest, and southern plains of the USA. A comparison of this summer to the dry summer of 2012 and the relatively wet summers of 2018 and 2021 was carried out using the National Centers for Environmental Prediction/National Centers for Atmospheric Research reanalysis, the Climate Prediction Center teleconnection indexes, and the blocking archive at the University of Missouri. The summer of 2022 was like that of 2012 which was characterized by a strong 500 hPa height anomaly centered over the western US and plains as well as very little blocking in the East Pacific. The summers of 2018 and 2021 were characterized by more zonal flow over the USA and more blocking in the East Pacific, similarly to the results of an earlier study. The teleconnection indexes for the prior spring and summer were largely similar for the two drier years and opposite for the wetter years. The surface conditions for the drier years were more similar while these were opposite for the wetter years. The integrated enstrophy (IE) used in earlier studies identified a change in the large-scale flow regime in early June 2022, which coincided with a decrease in the precipitation over the study region. However, one key difference was that the spring of 2022 was characterized by blocking more consistent with a wetter summer. This would have made the predictability of the drought of summer 2022 less certain.

In the Mediterranean and occasionally in the Black Sea, low-pressure systems with the character of both mid-latitude and tropical cyclones can form. These hybrid storms are called subtropical storms, subtropical depressions, medistorms/medicanes, or tropical-like cyclones (TLC). A strong low-pressure system given the name Falchion developed in northern part of the Black Sea during 11–20 August 2021. This storm was blamed for damage and more than 30 casualties in the nations bordering the region. At peak intensity, this storm was a as strong as a tropical depression. Falchion developed and moved northeast, reaching peak intensity before becoming nearly stationary. The NCEP reanalyses and satellite data obtained from Eumetsat’s geostationary satellite, Meteosat-8, were used to examine the character of the storm. This study demonstrates that the movement of Falchion was impeded by a blocking event that occurred over central Asia during much of August 2021. The storm did share characteristics with tropical systems, but a comparison of Falchion to tropical depressions and subtropical storms in the North and South Atlantic demonstrated that this storm was more consistent with these types of storms when examining the storm and the proximal environment. This included an examination of integrated water vapor (IVT) plumes, and the plume associated with Falchion did rise to the character of an atmospheric river in spite of the smaller scale.

Introduction. Almost every year, the territory of Ukraine is affected by drought of different intensity and duration, what is a favorable condition for wildfires. In the forest areas of the country arose about 106.8 thousand fires with a total area of 139.2 thousand hectares during 1990-2017. An analysis of the long-term dynamics shows that wildfires in Ukraine are a sustainable phenomenon. In 2020, under the severe drought conditions, 209 forest fires occurred, the most significant of them were in the Chernobyl zone and in the Lugansk region. Formulation of the problem. There is still no universally accepted method to describe all drought related processes due to complexity of drought phenomena. Although drought indices and fire weather indices usually have different time scales, their combination can be a basis in the prediction scheme in which the drought index acts as a background indicator, which enhances or decreases the current fire weather index. The purpose of this study is evaluate informativeness of a new fire weather index HDW (Hot-Dry-Windy Index) for the territory of Ukraine, which takes into account the main meteorological parameters necessary to describe the degree of wildfire danger due to weather conditions, so this index may become a component of the drought and fire monitoring system. Data and methods. The HDW index has a physical justification as the atmosphere affects the fire, namely, the combination of three atmospheric parameters characterizes the current conditions for the ignition and distribution of fire: wind, temperature, humidity. For the calculation of the HDW index, the data of GFS global numerical model with grid step 0.25 degrees is used. The calculation of the daily fields of the HDW index was carried out for the territory of Ukraine and for local areas. To localize areas of wildfires, in the study were used daily hotspots data provided by the web-resource Firms (https://firms2.modaps.eosdis.nasa.gov/), which are determined using satellite instruments MODIS (AQUA and Terra Satellites) and VIIRS (S-NPP and NOAA-20 satellites). Research results. Comparison of the calculated HDW fields in Ukraine with the position of hotspots showed that the maximum values of the HDW index are generally concentrated in fire areas. Comparison with the synoptic situation showed that the maximum values of the HDW are located in the zones of advection of warm and dry air in the lower troposphere and zones of strong surface winds, which usually correspond to the periphery of anticyclone or the warm sector of cyclone. The analysis of the time courses of the HDW index showed the typical feature, which expressed in the fact that in all cases there was an increase in the index values in the period before the wildfire, maximum of the HDW is fixed at the time of ignition and after that the index values sharply decreases. Scientific novelty and practical significance. The fields of new HDW index reflects the weather conditions typical for wildfires periods in the territory of Ukraine. The presence of specific features and extreme values in the index time course can be used to track the process of increase of fire danger under changing weather conditions to make short- and medium-range fire danger forecasts with evaluation of fire danger classes.