Climate variability, trends and extreme events in Ukraine

During the XX and the beginning of the XXI century, significant warming caused by the emission of greenhouse gases, mainly CO₂ and CH₄ into the atmosphere, is observed. The fifth assessment report of the Intergovernmental Panel on Climate Change estimated a warming of 0.85˚C ± 0.20˚C during 1880-2012. This global warming has been changing atmospheric circulation patterns, which can result in accelerating and intensifying extreme weather events such as more violent storms, floods, droughts, heat and cold waves. The weather extremes can cause economic loss, as well as loss of human lives.

In this study, the variations in 25 extreme temperature and precipitation indices defined by ETCCDI, are examined using probability distribution analysis and spatial statistics for periods of 71 to 137 years for 16 stations such as Ai-Petri, Askaniia-Nova, Chernivtsi, Feodosiya, Kerch, Kyiv, Lubny, Luhansk, Lviv, Mykolaiv, Odesa, Poltava, Shepetivka, Uzhhorod, Uman, Vinnytsia. The indices data were obtained from www.ecad.eu.

For Ukraine average, in the last 30 years, the number of summer days, warm days and nights, and warm spell duration index have reached historical highest values, while the number of cold days and nights, frost and icing days, and cold spell duration index reached the recorded lowest values.

The distribution characteristics of extreme temperature indices showed the increased frequency of warm events is higher in the west of Ukraine than in its others regions while, on the contrary, the decreased frequency of cold events is higher in the rest of the country than in its western part.

For all territory of Ukraine, an increase in maximum daily and maximum 5 days precipitation amount, the maximum number of consecutive wet days, heavy and very heavy precipitation days, and a decrease in the maximum number of consecutive dry days are observed for the last three decades.

A combination of harmonic regression and spectral analysis was applied to the time series for which the Mann-Kendal method revealed statistically significant trends, to predict the annual and seasonal temperature and precipitation, maxima of daily maximum temperature, minima of daily minimum temperature, maximum 1-day precipitation amount and consecutive dry days up to 2050.

The annual temperature was predicted to increase in the study area, with an increasing rate of 0.3-0.5°C decade⁻¹ up to 2050. The increasing rate of the maxima value of the daily maximum temperature is the same. Minima value of daily minimum temperature was predicted to increase the most from 0.44 to 0.62°C decade⁻¹. Seasonal values of all indices were predicted to grow, especially in summer and winter for maxima of daily maximum temperature and in spring for minima of daily minimum temperature.

Precipitation is predicted to increase in the range of 4 to 22 mm in decade⁻¹, the most increasing rate will be observed in stations located in the western and central parts of Ukraine. For the period up to 2050 for most of the territory of Ukraine time series of annual and seasonal maximum 1-day precipitation showed slightly increasing trends while the annual and seasonal consecutive dry days are anticipated to decrease insignificantly.