Along the East European Plain latitudinal transect, Scots pine tree-ring cellulose oxygen isotopes (δ¹⁸O_TRC) increases from north to south and consistently records significant summer hydroclimate signals. Although the dominant controls differ among regions, the northern chronology shows the strongest and most stable vapor pressure deficit signal. Compared with tree-ring width (TRW), δ¹⁸O_TRC better reflects regional climate information linked to atmospheric humidity and evaporative demand.