Extreme precipitation events in the NAM region—testing a modified convective parameterization scheme

The North American Monsoon (NAM) region is characterized by an abrupt summertime increase in precipitation due to strong convective activity and/or the passage of tropical cyclones. As early as May, intense rainfall begins over southern Mexico, and by July the NAM has migrated north into Arizona and New Mexico. It has been argued that climate change will increase the intensity of extreme precipitation events in the region. In this work we use dynamically downscaled simulations of historical (Reanalysis II) and future (UKMO-HADcm3 SRESA2) global climate models to investigate the potential effects of changes in precipitation extremes associated with a warming climate in the NAM region. Initial analyses using the statistical “peaks-over-threshold” approach evaluate the ability of WRF-downscaled Reanalysis to capture extreme events. Future changes in extreme events, associated to climate change, are also shown. Improved physical parameterizations will likely improve WRF's ability to capture extreme events. We present the modified Kain-Fritsch convective parameterization scheme for intense precipitation events in the region and show how the physically-based scheme improves upon the original version.