Given that rainfall extremes disproportionately affect the poorest countries, with large-scale damage to crops, habitation and risks to human health through water- and vector-borne diseases, being able to forecast future precipitation scenarios is highly desirable in attempting to mitigate the effects of climate change.

The Science article by A Pendergrass reviews current prediction tools and assumptions on the relationship between atmospheric moisture increase and rainfall extremes:

There are many ways to define extreme precipitation, and the choice of definition affects how it responds to warming. Researchers must choose their definition of extreme precipitation with care and articulate it clearly, and users should consider how extreme precipitation is defined when interpreting analyses of its change with warming.

We should expect moderate precipitation events to change more slowly than the rate of moisture increase in the atmosphere. On the other hand, the most extreme events might increase at or above the rate of atmospheric moisture increase, as studies have indicated in the case of Hurricane Harvey. The decision of what definition of extreme precipitation to use is important when climate change information is carried into other areas, such as engineering, socioeconomic impacts, adaptation, and policy. 

To view the full article see Science, Issue 6393.