Floods are a periodic natural phenomenon, often accompanied by negative consequences for the local population and the economy as a whole. Therefore, knowledge of the trends of maximum flow have great practical importance, because it is the basis for planning and designing various hydraulic structures, hydrological forecasting, the mapping of flood risk, etc. In this paper, we analysed the long-term cyclical fluctuations of the maximum flow of snow-rain floods of the Danube basin within Ukraine (5 large rivers, 14 medium and 5 small). The database includes time series (34 gauging stations) of the maximum discharges of the cold period from the beginning of the observations up to 2015. The methodological approaches (developed by Gorbachova) are based on the use of hydro-genetic methods − namely the mass curve, the residual mass curve, and combined graphs. The presented results illustrate that the longterm fluctuations of the maximum flow of snow-rain floods are synchronous at all study gauging stations in the Danube basin within Ukraine, but these fluctuations are not always in the synchronous phase. We found that the maximum flow of snow-rain floods in the Danube basin within Ukraine have four types of long-term fluctuations, each with a different cycle duration.

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In the current conditions of a changing climate, which directly affects the variability of river runoff, it is very important to have the knowledge about the trends of its extreme flow. Extreme low flows, just like floods are causing a significant material damage. The Tysa River has the two periods with the low flow during year. In addition, some years are dry and such years can be observed for several years in a row. This research used the Indicators of Hydrologic Alteration method (IHA) for investigation of extreme low flow characteristics and their changes along the Tysa River within Ukraine. The research was carried out based on the observations of 4 gauging stations that are located along the Tysa River within Ukraine. The mean daily discharges were used from the beginning of observations until 2018 inclusive. It turned out that at the Tysa River -Vylok Village gauging station the low flow trends differ from the trends at other gauging stations that are located in the upper part of the Tysa River.

Knowledge of maximum river runoff trends is of great practical importance, especially for design and operation of hydraulic structures. This article presents the results of the research of the Southern Buh River's maximum runoff. The water of the river is widely used for hydropower engineering, industrial and municipal water supply, agriculture, irrigation, shipping, tourism etc. The research of the maximum runoff was based on the Indicators of Hydrologic Alteration (IHA) method which is widely used in the whole world. This method enables calculation of quantitative statistical characteristics of rivers', lakes', reservoirs' runoff and determination of the degree of their hydrological regime changes. The IHA is used for water bodies having natural or regulated runoff. However, the IHA method was not widely used in Ukraine before. The purpose of this publication is using the Indicators of Hydrologic Alterations method in order to study the characteristics of maximum runoff and their changes along the Southern Buh River. The research was carried out based on the data of observations at 5 gauge stations located along the Southern Buh River. The research uses the mean daily discharges that has been recorded since the beginning of observations up to 2018 and 2019 inclusive. The river's runoff at each of gauge stations was divided into five components: "Extremely low runoff", "Low runoff", "High runoff pulses", "Small floods", "Large floods". This made it possible to separate three classes of high (maximum) runoff, for which the IHA statistics were calculated, from the total runoff. It was discovered that the long-term high runoff changes differed in each of its three components, although they had general trends. The most significant changes were found for large floods, with no significant changes found for high runoff pulses. General trends of high runoff showed that over time the values of maximum discharges tend to decrease, with the increasing duration of high runoff periods. The values of the main statistical indicators of high runoff gradually increase from the river's source to its mouth, which fully corresponds to the physical and geographical conditions of its formation. Nevertheless, some features of high runoff were still found. Thus small floods and high runoff pulses have the largest duration in the upper reach of the river. On average, the Southern Buh River experiences large floods once in every 10 years, small floods - once in every 2 years, high runoff pulses - 4-8 times a year in its upper reach and 9-14 times a year in its middle reach.

In the late 20 th century, warming on the Antarctic Peninsula was most pronounced compared to other parts of Antarctica. However, air temperature showed a significant variability, which has become especially evident in recent decades. Thus, the investigation of air temperature trends on the Antarctic Peninsula is important. This study examines the extreme air temperature at the Ukrainian Antarctic Akademik Vernadsky station, located on Galindez Island, Argentine Islands Archipelago, near the Antarctic Peninsula. For 1951 to 2020, based on the daily air temperature data, the temporal trends of extreme air temperature were analyzed, using 11 extreme temperature indices. Based on linear trend analysis and the Mann-Kendall trend test, the TXn, TNn, TN90p, and TN90p indices showed an upward trend, whereas theFD0, ID0, TN10p, TX10p, and DTR indices showed a downward trend. Among them, annually, FD0, ID0, and TN10p significantly decreased by -0.427 days, -0.452 days, and -0.465%, respectively, whereas TXn and TNn increased by 0.164℃ and 0.201℃, respectively. The indices TXx and TNn showed no statistically significant trends. The average annual difference between TX and TN (index DTR) showed a nonsignificant decreasing trend at -0.029℃ year -1 . Thus, for the period of 1951-2020, the Ukrainian Antarctic Akademik Vernadsky station was subjected to warming.