The North American Monsoon precipitation response to climate warming at convection-permitting scales.

Global climate models project a mean drying of the North American Monsoon (NAM) at grid spacings where convection is not explicitly resolved. We investigate the response of the NAM to climate warming at convection-permitting scales, utilizing output from a series of 13-year continental scale regional climate model runs performed at 4-km grid spacing. These include a control run forced by reanalysis and a pseudo global warming run that applies a mean perturbation to the boundaries derived from end-of-century changes projected by an ensemble of global climate models. NAM precipitation (June–September) shows averaged increases of 38.6% for portions of Arizona and western New Mexico. Over central Mexico, daily mean precipitation shows increases of 8.13%. Increases in rainfall amount are primarily associated with mean increases in precipitation intensity that overcome reductions in precipitation frequency. This increase in precipitation intensity is attributed to higher precipitable water concentrations, enhanced near-surface horizontal moisture fluxes off the Gulf of California, and stronger moisture flux convergence along the mountain peaks. Results from an offline semi-Lagrangian tracer model reveal that moisture contributions from the local land surface are significant in the control climate and produce proportionally less of the total precipitation in the warmed climate. Instead, contributions from nearby oceanic sources, notably the Gulf of California and Gulf of Mexico, increase. [ABSTRACT FROM AUTHOR]