HR: 1340h
AN: H33E-1418    [Abstracts]
TI: Stochastic Daily Rainfall Events and Their Role in Producing the Intraseasonal Extremes of Summertime Precipitation Over the Southwestern U.S.
AU: * Wang, J
EM: wjy@bu.edu
AF: Department of Geography, Boston University, 675 Commonwealth Ave., Boston, MA 02215 United States
AU: Anderson, B
EM: brucea@bu.edu
AF: Department of Geography, Boston University, 675 Commonwealth Ave., Boston, MA 02215 United States
AU: Salvucci, G
EM: gdsalvuc@bu.edu
AF: Department of Geography, Boston University, 675 Commonwealth Ave., Boston, MA 02215 United States
AB: Intraseasonal variability of summertime precipitation over the southwestern U.S. and its relation to slowly-evolving climate variations as well as high-frequency synoptic conditions are studied using chain-dependent empirical daily rainfall models. The simulated statistics for dry spells (defined as duration of dry periods), wet spells (defined as succession of wet days), and storms (defined as total precipitation over wet spells) are generated by the random evolution of a Markov Chain model with fixed intensity and frequency characteristics are compared with observations. Overall, the daily evolution of the Markov Chain model can explain more than 90% of the area-averaged variance for dry spells, 98% for wet spells, and 85% for storms, indicating that most of the intraseasonal events (i.e. wet/dry spells and storm amounts) in this region are not inherently predictable in that they are not related to year-to-year variations in the seasonal rainfall intensity and/or frequency characteristics. In addition, extreme events, which are defined as those events that lie outside the simulation capability of the stochastic Markov-chain model, only occur in 1-2% of the years for dry spells, <1% of the years for wet spells, and 4-6% of the years for extreme storms. Examining the changes in the seasonal frequency and intensity characteristics of rainfall during years with extreme dry spells indicates these are related to years in which the background climate conditions are conducive to producing anomalously low numbers of rainfall events. In addition, years with extreme storms are related to years in which the background climate conditions show significant changes in the intensity of events, although not necessarily the number of events. Interannual variations in the large-scale atmospheric and oceanic conditions associated with changes in these seasonal precipitation characteristics will be discussed and may help to improve the prediction of extreme events in summertime precipitation over the southwestern U.S.
DE: 1833 Hydroclimatology
DE: 1849 Numerical approximations and analysis
DE: 1854 Precipitation (3354)
DE: 1872 Time series analysis (3270, 4277, 4475)
SC: Hydrology [H]
MN: Fall Meeting 2005