Future Land Precipitation Changes Over the North American Monsoon Region Using CMIP5 and CMIP6 Simulations

Changes in the North American Monsoon (NAM), a circulation system that transports moisture into western Mexico and the southwest U.S., can have substantial impacts on water resources and agriculture. Here, we utilize future projections from Phase 6 and 5 of the Coupled Model Intercomparison Project (CMIP) to assess monthly changes in land precipitation and the leading mechanisms resulting from anthropogenic climate change. Historical CMIP6 simulations of seasonal precipitation demonstrate skill in reproducing NAM rainfall, but mimic precipitation biases observed in previous CMIP generations. Future climate projections from the SSP5-8.5 pathway produce reductions in precipitation that persist throughout the monsoon season (June-August) but are balanced by precipitation increases during the late monsoon season (September-October) but are not shown in CMIP5 projections. Atmospheric moisture budget analysis reveals that early monsoon rainfall deficits are associated with a combination of greater evaporative demand, a negative dynamic response of vertical moisture advection, and anomalous subsidence. Increases in late monsoon season rainfall are attributed to a positive change in the dynamical term of vertical moisture advection and increases in upward motion. Although minimal changes in total land NAM rainfall are observed, seasonal shifts and the persistence of drier conditions can have significant ecological and societal consequences.

Automated summary

This study utilizes model projections to find that the North American Monsoon (NAM) may experience reduced and shifted rainfall patterns in the future. Early monsoon season rainfall deficits are associated with increased evaporative demand, a negative dynamic response of vertical moisture advection, and anomalous subsidence. Increases in late monsoon season rainfall are attributed to a positive change in the dynamical term of vertical moisture advection and increases in upward motion. These changes can have significant impacts on the ecological and societal aspects.