The Role of CO2 Physiological Forcing in Driving Future Precipitation Variability and Precipitation Extremes

Abstract:

Transpired water contributes roughly 25% to total precipitation over the Earth’s land surface. In addition to transpiration’s impact on climatological mean precipitation, recent work suggests that transpiration reduces daily and intraseasonal precipitation variability in tropical forest regions. Projected increases in the concentration of CO₂ are expected to reduce transpiration through changes in plant physiology (termed the CO₂ physiological effect). Here, we use an ensemble of climate model experiments to assess the potential contribution of the CO₂ physiological effect to future changes in precipitation variability and extreme precipitation events. Within our model simulations, precipitation responses to the physiological effects of increased CO₂ concentrations are greatest throughout the tropics. In most tropical forest regions CO₂ physiological forcing increases the annual number of dry (less than 0.1 mm/day) and extremely wet (rainfall exceeds 95^th percentile) days. Changes in precipitation are primarily driven by an increase in surface temperature and subsequent changes in atmospheric stability and moisture convergence over vegetated tropical land regions. Our results suggest that the plant physiological response to CO₂ forcing may serve as an important contributor to future precipitation variability in the tropics, and that future work should aim to reduce uncertainty in the response of plant physiology to changes in climate.