Optimal ranking regime analysis of U.S. climate variablility. Part II: Precipitation and streamflow

Authors: Mauget, Steven; CORDERO, EUGENE - San Jose State University

Submitted to: Journal of Climate
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2014
Publication Date: 12/1/2014
Citation: Mauget, S.A., Cordero, E. 2014. Optimal ranking regime analysis of U.S. climate variablility. Part II: Precipitation and streamflow. Journal of Climate. 27(24):9027-9049.

Interpretive Summary: In the coming decades low frequency climate cycles may rival or even dominate the effects of greenhouse warming over some areas of the U.S. A better understanding of oceanic temperature cycles such as the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) and their effects over the continental U.S., that is, their timing, geographic location, and seasonality, requires that they first be correctly detected in observed data. Here, multi-decadal cycles in U.S. precipitation variability during 1896-2012 and streamflow variability during 1939-2011 are studied using a time series analysis method – the Optimal Ranking Regime method – that is particularly well suited to identifying the low frequency climate effects of these oceanic cycles. Before 1980 multi-decadal wet and dry periods in northwestern U.S. streamflow and annual precipitation roughly coincide with cool and warm sea-surface conditions associated with the PDO. After 1970 long-term wet periods that extend to recent years are apparent east of the Rockies in streamflow and annual precipitation, and also in fall precipitation. Correlations between time series U.S. precipitation and long-term sea-surface temperature (SST) data records during 1896-2012 show relatively extensive positive correlations between warming tropical SST and increasing fall precipitation over the eastern U.S. The possible Pacific and northern Atlantic roots of the recent eastern U.S. wet period are explored and discussed.

Technical Abstract: In a preceding companion paper the Optimal Ranking Regime (ORR) method was used to identify intra- to multi-decadal (IMD) regimes in U.S. climate division temperature data during 1896-2012. Here, the method is used to test for annual and seasonal precipitation regimes during that same period. In addition, water year mean streamflow rankings at 125 U.S. Hydro-Climatic Data Network gage stations are also evaluated during 1939-2011. The precipitation and streamflow regimes identified are compared with ORR-derived regimes in the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation (AMO), and indices derived from gridded SSTA analysis data. Using a graphic display approach that allows for the comparison of IMD climate regimes in multiple time series, an intra-decadal cycle in western precipitation is apparent after 1980, as is a similar cycle in northwestern streamflow. Before 1980 IMD regimes in northwestern streamflow and annual precipitation are in approximate anti-phase with the PDO. Post-1970 wet regimes are apparent east of the Rockies in streamflow and annual precipitation, and also in fall (SON) precipitation. Pearson correlations between time series of annual and seasonal eastern U.S. precipitation and SSTA analysis data show relatively extensive positive correlations between warming SST and increasing fall precipitation. The possible Pacific and northern Atlantic roots of the recent eastern U.S. wet regime are discussed.