HR: 0800h
AN: H21A-1328    [Abstracts]
TI: Changes in Seasonality of Streamflow in the Southwestern United States
AU: * Anderson, M T
EM: manders@usgs.gov
AF: U.S. Geological Survey, Arizona Water Science Center, 520 N Park Ave. Suite 221, Tucson, AZ 85719 United States
AU: Pool, D R
EM: drpool@usgs.gov
AF: U.S. Geological Survey, Arizona Water Science Center, 520 N Park Ave. Suite 221, Tucson, AZ 85719 United States
AU: Leenhouts, J M
EM: leenhout@usgs.gov
AF: U.S. Geological Survey, Arizona Water Science Center, 520 N Park Ave. Suite 221, Tucson, AZ 85719 United States
AB: The Southwestern United States receives about 50 percent of annual precipitation from summer thunderstorms generated by the North American Monsoon (NAM). Rainfall supplied during the summer monsoon helps sustain perennial flow and extend periods of intermittent flow in Southwestern streams. The National Weather Service (NWS) in Phoenix and Tucson define the seasonal onset of the NAM locally as the first day of a 3-day sequence of mean daily dew-point temperatures greater than 12.8 degrees Celsius and 12.2 degrees Celsius, respectively. Analysis of the NWS climatological criteria for Tucson indicates a progressively later average onset of the NAM from July 1 in the 1950s to July 9 in the early 2000s. Streamflow records were examined at several climate-sensitive gaging stations in Arizona and New Mexico (having 40 years or more of continuous record and no flow control) operated by the U.S. Geological Survey for evidence of flow alteration during the NAM season. Long-term records indicate that summer runoff (April 1 to September 30) is declining at many stations. The reduction may be in part caused by later onset of monsoon runoff. A later onset of monsoon runoff will have significant ecological consequences if the result is conversion of stream reaches from perennial to intermittent or ephemeral. For example, the San Pedro River in southeastern Arizona declined to zero flow July 6, 2005, as measured at the San Pedro River at Charleston gaging station, for the first time in recorded history. The period of zero flow persisted for 12 days. The cessation of flow at the Charleston station is of particular interest because perennial flow in some reaches of the San Pedro River is critical to maintain the ecological integrity of the San Pedro Riparian National Conservation Area. The onset of NAM in 2005 was among the latest in the Tucson climatological record. This late onset played a role in the zero-flow episode, although the importance of the late monsoon relative to other factors is not fully understood.
DE: 1807 Climate impacts
DE: 1813 Eco-hydrology
DE: 1833 Hydroclimatology
DE: 1880 Water management (6334)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
SC: Hydrology [H]
MN: Fall Meeting 2005