Tuesday, 13 January 2009
The Phoenix Rainfall Index (PRI)
Hall 5 (Phoenix Convention Center)
Phoenix, Arizona, is a vast, sprawling metropolis which covers an area of approximately 5000 km^2 (1900 mi^2). Historically, the “official” rain gauge for the Phoenix Metropolitan Area (PMA) has been situated near the center of the city. Since 1933, the official rain gauge has resided at Phoenix Sky Harbor International Airport (KPHX). While KPHX may have adequately represented Phoenix for the first half of the 20th century, it has become apparent that a single observation station can no longer properly represent the spatial and temporal distribution of precipitation over the PMA, especially during summer convective events associated with the North American Monsoon. In order to better represent rainfall across the PMA, and compare and contrast precipitation events over the PMA, a Phoenix Rainfall Index (PRI) has been created. The PRI, based on precipitation observed at 132 ALERT rain gauges across the PMA, incorporates both a spatial coverage term and a precipitation intensity/magnitude term. A ten-year climatology of Phoenix precipitation events reveals that the PRI sufficiently captures the annual trends in precipitation events across the PMA, while daily records adequately showcase extreme precipitation events. Daily calculation and dissemination of an index such as the PRI should be a very useful tool for the Weather and Climate Enterprise.