Understanding physical mechanisms associated with enhancement/reduction of extreme precipitation in a warming climate

As the climate warms, extreme precipitation may be enhanced or reduced, depending on changes to moisture (thermodynamical) and mass convergence (dynamical). Percentiles of precipitation are calculated using 6-hourly data from the Community Earth System Model (CESM) Large Ensemble (LENS) in both the present and a projected future (2071-2080) climate, along with the corresponding 3-D structures of water-vapor mixing ratio and mass convergence. This analysis allows an examination of how the 3-D moisture budget is projected to change for extreme events in a future climate. Precipitation extremes increase over most of the globe but decrease over some subtropical ocean regions. The sign of these changes to precipitation extremes is determined by the relative contributions of the dynamical and thermodynamical components of the moisture budget. The thermodynamical tendency is positive everywhere (i.e., it has a tendency to increase precipitation extremes) and relatively uniform with height, whereas the dynamical tendency changes between region, percentile of precipitation, and between different levels of the atmosphere. These results illustrate how thermodynamical and dynamical processes may offset or complement one another in a warming climate to alter precipitation extremes.