Soil solution salinity can decrease plant yield by means of transpiration reduction due to osmotic pressure and due to specific ion toxicity. Our understanding and predictions of root water uptake under conditions of salinity are commonly based on quantification of reduced uptake as a function of root zone salinity. Despite the fact that these functions are developed from full season, whole plant experimental data, they are often used in simulations that are time and space dependent. In a series of controlled crop growth experiments utilizing weighing-drainage lysimeters where plants were grown while irrigated with varied levels of irrigation water salinity, we have measured daily evapotranspiration (ET) and related it to the potential demand for transpiration based on climate data (VPD). Data analysis suggests that the magnitude of plant response to salinity increases as a function of increasing climate demand. Under times of higher VPD the reduction of transpiration is greater for equal increases in root zone salinity. Furthermore while studying plant response to salinity, seasonal variation in the response needs to be considered because the impact of salinity on ET and growth is a time-integrated, dynamic process. We discuss implications for agriculture and water management and present a method to incorporate dynamic, climate-coupled salinity reduction functions in a numerical model.