Past studies have shown that the physiological effect of CO₂ may be important for future climate change, yet many regional climate models and hydrological models used in impact studies do not simulate it. Here, the role the physiological effect of CO₂ on the changes in the continental hydrological cycle over Europe in summer – when severe drying is projected – is assessed using a large ensemble of idealized climate simulations, and compared to the radiative impacts of CO₂. As expected, the physiological effect of CO₂ leads to a decrease in evapotranspiration. However, it generally does not lead to an increase in river flows or soil moisture as often expected, because it is also associated with a large decrease in precipitation. This decrease in precipitation is likely due to small warming and decrease in specific humidity caused by the physiologically driven decrease in evapotranspiration, which together lead to a large decrease in relative humidity. Important inter-model uncertainties, however, exist regarding the physiological impact of CO₂ on the summer hydrological cycle over Europe.

过去的研究表明，CO ₂的生理效应可能对未来的气候变化很重要，但影响研究中使用的许多区域气候模型和水文模型并未对其进行模拟。在这里，使用大量理想化气候模拟并与 CO ₂的辐射影响进行比较，评估了 CO ₂对夏季欧洲大陆水文循环变化的生理影响（预计会出现严重干燥）。正如预期的那样，CO ₂的生理作用导致蒸发量减少。然而，它通常不会像通常预期的那样导致河流流量或土壤湿度的增加，因为它也与降水的大量减少有关。降水量的减少很可能是由于生理驱动的蒸发蒸腾量减少引起的小幅变暖和比湿度的降低，这两者共同导致了相对湿度的大幅下降。然而，关于 CO ₂对欧洲夏季水文循环的生理影响，存在重要的模型间不确定性。