Precipitation change under global warming and interpreting the rich-get-richer effect: issues at regional scales and large event sizes

Precipitation changes under global warming are often discussed in terms of wet areas receiving more precipitation and dry areas receiving less, sometimes termed the "rich-get-richer" effect. Since the first explorations of this, it has been known that contributions can be broken diagnostically into a relatively straightforward tendency associated with moisture increases acted on by the climatological circulation and dynamical feedbacks associated with changes in circulation. A number of studies indicate the latter to be prone to yield scatter in model projections of precipitation change. At regional scales substantial contributions from dynamical feedbacks tend to occur, affecting our ability to make statements, for instance, at the scales of major monsoon regions or of the southwestern North American coastal regions. Contributing to this in the tropics is a battle between two terms of the gross moist stability, involving lower tropospheric moisture versus height of convection, while at mid-latitudes zonal asymmetry in storm tracks can be significant. Factors affecting large scale versus regional dependence will be reviewed, including the contributions of Isaac Held, with an eye to asking how the community can make succinct statements without oversimplifying the challenges. A simple prototype model for event size distributions indicating ways in which large event sizes may change relative to the rest of the distribution will also be noted.