Non-Linear Extreme Precipitation Response to CO2 Forcing

Hydrological sensitivity is typically defined as the global mean precipitation response divided by the global mean temperature response, and it has been shown to remain constant across multiple CO2 doublings. Meanwhile, the “wet tail” of the precipitation distribution, which represents extreme precipitation, is projected to increase more rapidly than the global mean precipitation in 21st-century scenarios involving increasing CO2 and other anthropogenic forcings. Some studies have identified a correlation across models between an increase in extreme precipitation and a decrease in the “dry tail” (extreme low values) of precipitation, highlighting the importance of considering the changes in the daily precipitation intensity distribution and its tails under CO2 increase scenarios. However, changes in the daily precipitation intensity distribution as a function of CO2 forcing have yet to be fully explored. To address this gap, we utilize Earth system model simulations from different modeling centers with varying levels of CO2 increase and decrease (1/8x, 1/4x, 1/2x, 2x, 4x, and 8xCO2), to investigate the linearity of precipitation distribution tails in response to CO2 forcing. Our findings reveal that the wet tail of the precipitation distribution, associated with extreme precipitation, increases more strongly than the mean, while the dry tail, related to dry days, increases less than the mean or even decreases in some seasons. Additionally, we decompose the response by regional land areas for each season and analyze the contribution of thermodynamic and dynamic responses to the observed changes in the precipitation distribution.