Long-term meteorological data and isotopic composition in precipitation, surface water and groundwater revealed hydrologic sensitivity to climate change in East Ukraine.

Our study focused on the incorporation of stable isotope ratios in water in climatic and hydrological observations to understand local hydroclimatic processes and determine basic hydrological sensitivity to climate change in East Ukraine. Long-term meteorological data from two stations at Kharkiv and Izyum showed that air temperature was significantly increased only for the cold period (November-April), while precipitation amount increased during all seasons. Applying two-component mixing model with stable isotope ratios in water, we determined that surface water in both regions was dominantly recharged by the cold precipitation. The highest share of cold precipitation contribution (∼79 %) was found in the river with the shortest water transit time. The isotopic signature of groundwater also indicated that water resources were mainly recharged during the cold period. Our findings reveal that basic hydrological sensitivity of the transboundary (Ukraine/Russian Federation) Seversky Donets River basin relates to hydroclimate changes mainly observed in November-April. We suggest that climate changes can influence surface water and groundwater but also the overall regional water availability that is highly dependent on the cold precipitation in these regions.