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On linkages between precipitation change and cloud feedbacks

Presentation Date
Thursday, December 15, 2022 at 3:00pm - Thursday, December 15, 2022 at 3:10pm
McCormick Place - E450a



Prior studies have suggested various hypotheses for ways in which hydrologic sensitivity (HS; global change in precipitation per degree of warming) and changes in clouds might be interconnected. For example, one study suggests a pivotal role for low clouds in HS spread (Watanabe et al. 2018) while another points to tropical high clouds as the controlling factor (Su et al. 2017). However, HS is made up of geographically diverse changes to the precipitation distribution including enhanced extreme precipitation and reduced light-moderate precipitation. Moreover, past work tells us that models with a stronger intensification of extremes (ΔP>99/ΔT) experience a greater reduction in non-extreme precipitation (ΔP<99/ΔT) (Thackeray et al. 2018). Given that extreme precipitation is generally associated with higher cloud tops while lighter precipitation is associated with lower clouds, we hypothesize that this “precipitation compensation effect” should contribute to reductions in low cloud cover under warming. Here, we explore interactions between various aspects of precipitation and cloud changes across the CMIP6 ensemble. We also break down global cloud feedback into various components (e.g., shortwave, longwave, low cloud, non-low cloud). Notably, we find a strong positive correlation between global ΔP>99/ΔT and both low cloud and shortwave feedback strength. Cross-model correlation maps reveal that reduced clouds in the extratropics primarily drive this relationship. Moreover, it is the change in the SH midlatitudes that broadly coincides with areas where the “precipitation compensation effect” is strongest. This suggests that increased extreme precipitation (greatest in the equatorial Pacific) and the compensatory effects it has on light-to-moderate precipitation may play a role in future reductions to SH midlatitude cloud cover. We offer possible reasons for this connection and investigate the role of changes in precipitation efficiency and cloud lifetime.

Funding Program Area(s)