"Our ability to predict consequences of climate change on the physical, chemical and biological characteristics of water resources in high-latitude uplands is a formidable challenge. These regions are highly sensitive to climate induced changes as small differences in temperature determine the status of frozen ground, the state of precipitation, and the magnitude and timing of snow accumulation and melt. Recent findings in mid-latitude regions suggest that there exist “two water worlds” – mobile water expressed in the stream and tightly bound water represented by plant water – which means that a substantial proportion of precipitation that infiltrates the soils becomes isolated from discharge to the streams, indicating that the composition of stream water alone is insufficient to understand routing and transit times of water in catchments. These findings challenge the core assumptions in our perceptual models of how we think biophysical systems work and how we make predictions of water partitioning of how inputs of water are evaporated, stored and reach the streams. High-latitude headwater catchments are characterised by lower evapotranspiration, consequent lower soil moisture deficits and different seasonality than mid-latitude sites. This interdisciplinary proposed project will address novel questions on vegetation-water linkages by using isotopic tracers in different waters as ""fingerprints"" across different spatial scales along a climate gradient as a precursor to understand future response to change in high-latitude upland catchments. The proposed project will – for the first time - examine the mechanisms of water storage, transmission and release and possible implications of climate change in high-latitude ecosystems along a cross-regional transect. Such geographically extensive comparison has never been conducted in these environments. This allows the consistency of processes and drivers to be assessed across broad spatial scales."