Climate change in the UK has affected growth, structure and distribution of trees and woodlands. Climate change projections for the UK are for wetter winters, drier summers and significance changes in temperature regimes. Hence, it is imperative to determine species-specific responses to predicted changes in summer rainfall and provide further understanding of the changes in growth and development in response to a decrease in water availability. The study on silver birch (Betula pendula Roth) and downy birch (Betula pubescens Ehrh.) showed that plant height, plant diameter, biomass and moisture content reduced significantly with increased water stress. The stressed plants had lower stomatal conductance, transpiration and net CO2 assimilation than plants in the controlled treatment. B. pendula showed higher height and diameter growth, lower shoot-to-root ratio and superior physiological traits indicating that this species can perform better than B. pubescens in future water-deficit conditions.