Decrease of the global precipitation area in CMIP6 projections

Reanalysis as well as satellite data from TRMM show a decreasing trend in the daily precipitation area between 50°S and 50°N throughout the past decades. The trend is highly correlated to global mean temperatures and indicates the change in the hydrological cycle may be connected to the warming climate, resulting in increased drought frequencies and more intense rainfall. However, changes in the satellite networks provide inhomogeneous data sets and have possibly affected the precipitation area in the satellite and reanalysis dataset. Global climate and Earth system models, although suffering from biases in precipitation amounts and frequencies, are not influenced by changing observation systems. Thus, they provide a possibility to test the hypothesis of a decreasing precipitation area in a warming climate.

Here, we have used simulations from CMIP6 and CMIP5 to test this hypothesis. The models following the high-emission scenarios SSP5-8.5, SSP3-7.0 and RCP8.5 showed a clear decrease in the precipitation area towards the end of the 21st century. Compared to changes in the satellite and reanalysis data, the magnitude in the CMIP models was smaller. The decrease was apparent globally but most pronounced between 50°S and 50°N. Zonal averages of the daily precipitation area showed a general decrease from 5° to 50° on both hemispheres and an increase from 55° towards the poles, indicating a poleward shift of precipitation. In the Arctic region, the daily precipitation area was increasing from 20% to 30% on average.

Along with the precipitation area changes, the precipitation frequency decreased between 5° and 50 °S and increased in the polar regions. In the Northern Hemisphere, the precipitation frequency decreased over the North Atlantic, the Mediterranean region and Middle America. At the same time, precipitation intensity increased mostly everywhere.

Our analysis supports that in a warming climate, the daily precipitation area may indeed shrink, as found in reanalysis and satellite data. The results also showed that an increase in precipitation is coupled with an increase in precipitation intensity, while a decrease in precipitation is coupled with a decrease in frequency. However, the latter was generally coupled with an increase in precipitation intensity, suggesting increased drought frequencies and more intense rainfall at the same time.