Elevation‐dependent precipitation response to El Niño‐Southern oscillation revealed in headwater basins of the US central Rocky Mountains

Abstract

AbstractWe used nonparametric analyses of gridded precipitation data from the Parameter‐Elevation Relationships on Independent Slopes Model (PRISM) to examine teleconnections between the El Niño‐Southern Oscillation (ENSO) and elevation‐related precipitation variability from 1950 to 2016 over the Snake‐Salt, Wind‐Bighorn, Green, and Platte basins, which span the North American continental divide. Our analyses parse data into three‐month‐long meteorological seasons and use the Japan Meteorological Agency (JMA) index to examine seasonal precipitation during El Niño and La Niña years. The results reveal statistically significant elevation‐related variability in seasonal precipitation response: ENSO‐related differences in precipitation were most widespread during winter, with below‐normal precipitation during El Niño and above‐normal precipitation during La Niña. These connections were particularly clear, with p‐values <.01, in analyses focused on high elevations, where most precipitation falls. Hence, the most apparent ENSO‐related impacts on precipitation were observed during months and at elevations that are crucial to snowpack growth. In addition, our analyses of low elevations of the Platte Basin reveal above‐normal spring and fall precipitation during El Niño and below‐normal fall precipitation during La Niña. Comparison of PRISM and North American Regional Reanalysis (NARR) datasets for the period of overlap (1979–2016) suggest that the elevational response is robust. Together, our findings expand the scope of documented ENSO teleconnections in western North America and underscore the importance of parsing precipitation response over temporal and spatial scales that are relevant to the timing and location of dominant precipitation inputs in the topographically diverse western United States.