Impact of elevated CO2, temperature, and drought on summer ecohydrological moisture cycling and water transit times in montane grassland

Rapid alteration of Earth’s climate amplifies concerns over the future quantity and quality of freshwater resources. Earth’s warming atmosphere is known to store and transport more water vapor at higher velocities than historic climatic conditions, augmenting the magnitude and frequency of extreme weather events like intense rainfall and droughts. Warming can accelerate evapotranspiration by elevating vapor pressure gradients, whereas atmospheric CO₂ enrichmentcan suppress transpiration as plants preferentially close their stomata. Despite the potential hydrological implications, no study to date has comprehensively explored how these global change factors, when combined, impact the transit of moisture through the soil-plant-atmosphere continuum. In a montane grassland we tracked an extensive deuterium-labelled rainfall event following a severe experimental drought period under current versus simulated future (+300 ppm CO₂ and +3°C warming) conditions. We monitored stable isotopes of water in soil and evapotranspiration vapor, to partition signatures of evaporation, transpiration, drainage and soil pore water and quantify transit times through each ecohydrological compartment. Preliminary results suggest that under future conditions (+300 ppm CO₂ and 3°C) drought can drastically increase the retention time of water in the rootzone, which intermittently forces plants to return older water to the atmosphere. We intend to use these findings to directly quantify the water age preference of evaporative and drainage fluxes under a range of climate scenarios.