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Future precipitation changes include contributions from both thermodynamic and dynamic processes. Given that precipitation in the tropics is commonly associated with convergence lines, we construct a simple linear regression model relating the convergence line frequency and strength to precipitation at subdaily time scales, and use it to show that changes in the convergence lines are related to the dynamic change in the precipitation. Given GCM-predicted convergence line changes, we predict precipitation changes using the regression model. The so-predicted precipitation change is equivalent to the dynamic component of the precipitation change identified in earlier studies that used very different methods. The difference between the precipitation change in GCMs and that predicted from changes in convergence lines accounts for thermodynamic and other potentially important dynamic contributions. More accurate predictions of future precipitation therefore require the accurate simulations of the relatively short-lived weather features responsible for convergence lines in the tropics in GCMs.

Plain Language Summary Future changes in precipitation have been shown to have contributions from both thermodynamic and dynamic processes. Although the thermodynamic part is reasonably well understood (through the Clausius-Clapeyron relationship), the dynamic part is not. Moreover, the spatial pattern of the precipitation change and much of the regional uncertainty in projections of this change, especially in the tropics, are dominated by the dynamic contributions. Therefore, we have investigated the underlying processes for the dynamic part and discovered that changes in the weather of atmospheric convergence lines constitute a large part of the dynamic contribution to precipitation changes in a future climate. The implications of this are not only that we now know the main ingredient for change, but also that it is the weather time scales that we need to simulate well in models for us to predict this important contribution to climate change.