Precipitation extreme changes exceeding moisture content increases in MIROC and IPCC climate models

Abstract

Precipitation extreme changes are often assumed to scale with, or are constrained by, the change in atmospheric moisture content. Studies have generally confirmed the scaling based on moisture content for the midlatitudes but identified deviations for the tropics. In fact half of the twelve selected Intergovernmental Panel on Climate Change (IPCC) models exhibit increases faster than the climatological-mean precipitable water change for high percentiles of tropical daily precipitation, albeit with significant intermodel scatter. Decomposition of the precipitation extreme changes reveals that the variations among models can be attributed primarily to the differences in the upward velocity. Both the amplitude and vertical profile of vertical motion are found to affect precipitation extremes. A recently proposed scaling that incorporates these dynamical effects can capture the basic features of precipitation changes in both the tropics and midlatitudes. In particular, the increases in tropical precipitation extremes significantly exceed the precipitable water change in Model for Interdisciplinary Research on Climate (MIROC), a coupled general circulation model with the highest resolution among IPCC climate models whose precipitation characteristics have been shown to reasonably match those of observations. The expected intensification of tropical disturbances points to the possibility of precipitation extreme increases beyond the moisture content increase as is found in MIROC and some of IPCC models.

Fig. 1.

(A) Inverse cumulative distribution functions CDFs of daily precipitation over the tropical (30°S–30°N) oceans from the high-resolution version of MIROC and the observational dataset GPCP 1DD (1997–2005). The vertical dotted lines represent the CDF values that correspond to the return periods of 1, 10, and 100 yr. (B) Fractional changes in precipitation per unit warming of the target area.

Fig. 2.

(A) As in Fig. 1B but for the selected models from the WCRP CMIP3 multimodel dataset. Here the fractional changes of climatological-mean precipitable water (shown within the parentheses in the legends) have been subtracted from each model’s fractional changes of precipitation. (B) As in (A) but for 30–60°N.

Fig. 3.

(A) Fractional changes in variables composited with respect to precipitation levels corresponding to each CDF value for the high-resolution version of MIROC. This figure focuses on ocean grid points in the 30°S–30°N zonal band for all seasons. Variables analyzed are: precipitation (P), precipitation minus evaporation (P - E), convective precipitation, large-scale condensation, precipitable water (W), and vertical motion at 500 hPa (w). Percentage changes are normalized by the temperature increase in the area in question; we have omitted the denominator dT in the legend. (B) As in (A) but for other variables. The coefficient a is the gross moisture stratification divided by precipitable water, and the coefficient b represents the scaling of (9). See the method for detail.

Fig. 4.

As in Fig. 3B but for other CMIP3 models. Model names are plotted at the top of each panel.