Long-Term Variability of Extreme Summer Monsoon Precipitation in the Semiarid Southwest United States

In the Southwest USA, summer convective precipitation from the North American Monsoon provides approximately 60% of total annual precipitation. To capture the high intensity and isolated nature of monsoon storms, the USDA-ARS Walnut Gulch Experimental Watershed (WGEW) has been measuring precipitation with a network of more than 90 rain gauges across a 150 km² area, with measurements dating back to the 1950’s. Climate model simulations project an increase in precipitation intensities as the atmosphere water vapor holding capacity changes and circulation dynamics shifts. However, natural low-frequency climate variability and the localized nature of summer convective storms make difficult to identify trends in precipitation intensities leading to inconclusive findings. This study focuses on the impacts of those changes on the long-term variability of sub-daily and daily summer (July-August-September) precipitation intensities and storm characteristics. We use an Annual Maximum Series (AMS) and a Partial Duration Series (PDS) approach to identify temporal trends in maximum intensities for durations ranging from 5- to 1440-minutes and interstation correlations decays to evaluate changes in spatial precipitation patterns.