Phase and Amplitude Changes in Rainfall Annual Cycle Over Global Land Monsoon Regions Under Global Warming

Land monsoon rainfall has a distinct annual cycle. Under global warming, whether the phase and amplitude of this annual cycle would be changed is still unclear. Here, a global investigation is conducted using 34 CMIP6 and 34 CMIP5 models under a high emission scenario. Seasonal delays would occur in the Southern Hemisphere (SH) American (3.43 days), Northern Hemisphere (NH) African (5.98 days) and SH African (3.76 days) monsoon regions, while no robust signal is found in other monsoon regions. Except NH American monsoon, amplitude is enhanced in all the monsoon regions. Compared to amplitude, the phase changes dominate the future changes of precipitation in the SH American, NH African and SH African monsoon regions. In these phase-dominated regions, atmospheric energetic framework is proved to be reliable at regional scale and the enhanced effective atmospheric heat capacity is found to be the dominant factor. Monsoon rainfall sustains nearly two-thirds of the world's population. The arrival timing and the difference between maximum and minimum of monsoon are the main features of concern. We revealed that rainfall would be delayed over the Amazon, Sahel and South Africa and enhanced in most monsoons except North American monsoon under global warming. In the Amazon, Sahel and South Africa, future changes of the arrival timing can be more remarkable compared to the changes of range. These regional changes can be resulted from physical constraints related to atmospheric energy under global warming, which was previously proposed at larger scale and has been proved to be reliable here at regional monsoons. Precipitation would be robustly seasonally delayed over the South American, North African and South African monsoons under global warming The phase delays would dominate precipitation annual cycle changes in the above three regions, while amplitude changes dominate the others The enhanced effective atmospheric heat capacity under warming is key to the seasonal delay of precipitation at the phase-dominated regions