Selection of representative climate simulations to assess near-future climate change in Odesa, Ukraine

The past climate change impact on some natural objects is usually studied using available observations or re-analysis data. To assess future climate changes, the only source of information is simulations of global or regional climate models. A particular application depends on the problem to be studied - if the natural object needs to be considered in more detail, then a smaller spatiotemporal grid step in a model must be used. The present study focuses on the methodology for selecting representative simulations from the EURO-CORDEX ensemble by RCP8.5 scenario and assessing near-future temperature and precipitation trends in Odesa, Ukraine.

The approach is to minimize bias in average monthly temperature and precipitation. The 1970–2005 average bias by 76 simulations of the EURO-CORDEX ensemble is about +0.5÷+1.0 °C for the monthly temperature and about –25÷+10 mm for the monthly precipitation sum. The preferably positive bias for precipitation is registered from October to March and a negative one – from April to September with a minimum in July-August. Some models can show almost dry summer, which is not in fact.

The procedure for selecting representative simulations involves choosing the minimum bias in the reference period 1970-2005 and adjusting the results obtained for the scenario simulation period 2006-2020. Minimizing the mean bias allowed the selection of the eight simulations that satisfactorily describe changes in temperature and precipitation over the period 1970-2020. These simulations were then used to assess the near-future climate in Odesa.

The mean temperature in Odesa has increased by ~1 °C over the past 30 years. A significant trend towards an increase in the average annual temperature will continue in 2021-2050, and the temperature will also increase for all months. There exists only little probability of a negative average monthly temperature and only in January. Although the average annual precipitation sum will increase slightly (~ 20 mm), it will decrease significantly in summer and increase in spring and at the end of the year. In general, it seems that the climate of Odesa is moving towards the Mediterranean climate – warm to hot, dry summers and mild, moderately wet winters.