<p>The last decade proved to be the warmest in Ukraine for the whole period of instrumental weather observations. Recent and projected future warming will cause changes in the duration of climatic seasons in Ukraine with corresponding shifts in dates of their start and end.</p> <p>As specified by the Expert Team on Climate Change Detection and Indices, climatic seasons are determined as periods from the first day after the start of a year to the first date after 1 July when at least 6 consecutive days mean daily temperature (t) exceeds (drops under) different thresholds. We analysed four climatic periods: warm period (t>0<sup>o</sup>C), growing season (t>5<sup>o</sup>C), active vegetation (t>10<sup>o</sup>C), and summer season (t>15<sup>o</sup>C).</p> <p>To assess these projected changes bias-adjusted daily data of EuroCORDEX were used from 34 regional climate models for RCP4.5 and RCP8.5 scenarios for 3 future periods: near-term 2021-2040, mid-term 2041-2060 and far-term 2081-2100. Data of ensemble mean for two scenarios firstly were compared with E-Obs v20.0e results in the base period 1991-2010 and showed different biases for different climatic seasons, but very similar behaviour for both scenarios and both variables (length and start of climatic seasons). The least biases (< 0.5 days) were obtained for growing season, while biases reached -10 days for length of warm season and were within 1-3 days for other two seasons.</p> <p>In general by the end of the century, under the RCP4.5 scenario in Ukraine, all analysed climatic season lengths may be the same as in the middle of the century under the RCP8.5 scenario.</p> <p>By the end of the century, for the RCP8.5 scenario, the changes in the climatic seasons range from 40 to almost 70 days, increasing from east to west. As a result, in the coldest in Ukraine region winter is projected to last only from 10 to 30 days, and the vegetation will last throughout the year not only at the southern coast of the Black Sea but also the steppe part of the Crimea and some southern parts of Odesa region. There are almost no differences between scenarios for growing season length, start and end days in the near-term. The area with the longest growing season (from 240 to 260 days) will extend almost 200 km to the north.  </p> <p>Under the RCP8.5 scenario, the length of active vegetation at the end of the century can range from 200 to 240 days, and in the Crimea and the south of Odesa region - 240-285 days, and summer length can vary from 140 days in the north to over half-year in the Crimea and southern Odesa. At the end of the 21<sup>st</sup> century, projected summer in Polissya will be as in the Crimea now - 140-160 days. Such climatic conditions were not observed in Ukraine previously. Increasing the length of the growing season and the period of active vegetation will strengthen the agro-climatic potential of Ukraine and contribute to obtaining higher yields of crops if corresponding measures in providing enough water supply will be implemented.</p>

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<p>Climate change is one of the major challenges for future development in every country including Ukraine where actual warming already has impacted many sectors, population, and ecosystems. Recently, the International Initiative of Coordinated Downscaling Experiment for Europe (Euro-CORDEX) has provided RCM data for 0.1<sup>o</sup> grid. This detailed RCM projection dataset is an excellent basis for estimation of exposure and vulnerability to climate change of different objects and for updating projections for a new National Communication of Ukraine to UNFCCC as well as for Strategy of Ecological Safety and Adaptation to Climate Change in Ukraine.</p><p>The study is focused on the estimation of the essential and special climatic characteristics and their changes in the near future (2021-2040) as well as to the middle (2041-2050) and end (2081-2100) of the century over the base period 1991-2010 for three scenarios: RCP2.6, RCP4.5, and RCP8.5. We used bias-adjusted RCM data for daily maximum, mean, and minimum temperature and precipitation provided via ESGF web-portal. We applied a multi-model ensemble approach with further bias-correction by delta-method for multi-year monthly values of the essential characteristics as well as calculated climatic indices using a gridded observational dataset of E-Obs v.20.0e. Ensembles for RCP4.5 and RCP8.5 consisted of 34 RCMs while for RCP2.6 only data of 3 RCMs were available. That is why RCP2.6 is only indicative, while the other two scenarios results have a high confidence level and quartiles and percentiles of the ensemble range are estimated.</p><p>More consistent temporally and spatially results were obtained for temperature projections. Increases relative to the baseline were in the range of 0.5-1.5ºC for all the RCPs with a bit higher warming in the North of the country in 2021-2040. In 2041-2060, the increases were 1.0-2.0ºC under RCP2.6 and 1.5-2.5ºC under RCP8.5, with RCP4.5 in between. By the end of the century 2081-2100 the differences between scenarios became much pronounced: from 1-2ºC for RCP2.6 to 4-6ºC for RCP8.5.</p><p>Precipitation changes are much complex with high variability across the seasons and the territory. In winter precipitation tends to increase relative to the baseline in most of the country for all the RCPs. In early spring (March) there is a relative decline in the near-future period, especially in RCP2.6 and RCP8.5 but not in RCP4.5. In later periods the decline becomes less and in the higher RCPs, there is a relative increase. Later spring rainfall changes show a decline in RCP2.6 but an increase for the other RCPs. The summer months show a relative decline with all the higher RCPs getting drier over time. In the fall relative changes are mixed, with declines in some months and increases in others.</p><p>Based on these two essential climatic characteristics other important indices were calculated and analyzed: length of vegetation season, tropical nights, summer days, water deficit, aridity/humidity index, etc.</p><p>Obtained projections of climatic characteristics were(will be) used for further agriculture, forest, and human health impact assessments, that will be the basis for the development of adaptation measures to climate change in the frames of the National Adaptation Plan of Ukraine.  </p>

<p>The updated climate projections with fine spatial resolution of 0.1⁰ allow to evaluate more precisely regional features as climate change impacts unevenly on various geographical regions. The analysis performed for understanding the quantitative changes of climate characteristics for indicating climate extremity in cold season and daily (DTR) and annual (ATR) temperature ranges, and Ivanov index of thermal continentality (IITC) for Ukraine that can be used as the additional information for economic sectors. This research is based on the observational E-Obs v20.0e dataset and ensembles of 34 RCMs for RCP4.5 and RCP8.5 using the base periods of 1961-1990 and 1991-2010, and future ones – near-term (2021-2040), mid-term (2041-2060), and far-term (2081-2100). All characteristics were averaged for each 20-year period and bias-adjusted with applying the delta-method for avoiding and smoothing unnecessary fluctuations. It has been found that the general tendency for ATR will be decreasing with value 1-2°C and shifting from the west to the east for RCP4.5 and RCP8.5. It could be explained by the general trend of temperature increase and possible shrinking of temperature contrasts between the warmest and the coldest months. In comparison to ATR, DTR has low variations and not such apparent changes. They were detected in some regions with values up to 1°C. According to the results, IITC slightly variates over the region during the studied period, but the continentality increases in south-eastern regions of Ukraine based on RCP8.5 scenario in 2081-2100. In addition to, extreme temperature changes such as numbers of frost (FD) and ice days (ID) have been analyzed. They refer to cold season and are indicators of the harshness of the climate. Selected periods of climate projections allow to analyze the dynamics of climate change. Air temperature rise will provoke a significant decrease in the FD determined by daily minimum temperature (mostly in nights) during cold season up to 2100 for both scenarios. According to RCP4.5, the FD could decrease by the end of the century from 22 in the south to 34 nights or more in northern part of Ukraine. For the RCP8.5 scenario, FD possibly shorten by minimum 40 days on the coasts of Black and Azov Seas to 64 days or more in the north. To sum up, the FD will variate from 30 to 60 a year in Ukraine, except for the Carpathians and the east-northeast. For ID determined by daily maximum temperatures, maximum reduction of over 20 days are projected in the Carpathians and north-eastern part while they are from 15 to 20 days resulted in average 30 ice days per year for the most territory of the country based on RCP4.5. Substantial decrease in ID comparable with the recent one is projected in RCP8.5 till the end of the 21st century. It will result in less than 30 ID at most in northeast part for the country, only 10 days more in the coldest part of the Carpathians and extremely low number of ice days for the warmest part of the country namely Transcarpathia, the south and south-west.</p>

<p>Regular update of climate projections is a crucial task in all countries since such data should be a basis for development further adaptation measures on all levels from national down to local. And the more detailed data is available the more reliable and focused measures to combat climate change could be developed. At the moment data of EuroCORDEX initiative with 0.1<sup>o</sup> spacing is the most suitable, detailed and freely available dataset for Ukraine. We used bias-adjusted daily and monthly air temperature and precipitation datasets projected by 34 regional climate models (RCMs) for RCP4.5 and RCP8.5 scenarios for 3 future periods: near-term 2021-2040, mid-term 2041-2060 and far-term 2081-2100. Further bias-adjustment by the delta-method has been applied for the RCMs ensemble means when differences in temperatures (or ratio in case of estimations for precipitation) in future periods were added to (or for precipitation - multiplied by) values in the base period 1991-2010, obtained from the E-OBS v20.0e data. The Delta method applied provides more reliable results and allows to effectively exclude systematic biases in RCMs.</p><p>At the same time, in response to practical needs not only main climate parameters such as air temperature and precipitation should be projected under different scenarios but specialized climate indices that are different for different sectors. We’ll present as an example a set of indices relevant to forestry which is among the most vulnerable sectors to climate change in Ukraine. They are as follows: daily and annual temperature ranges, continentality, the coldest month temperature, heat and moisture supply during warm season with t>0<sup>o</sup>, and types of climates by Worobjov index. All climate indices for the base period 1991-2010 and past WMO period 1961-1990 are estimated from the E-OBS data. To visualize the above indicators Ukraine atlas has been developed in QGIS application which represents 2 past and 3 future periods for 2 scenarios.</p>