Influences of Atlantic multidecadal oscillation phases on spatial and temporal variability of regional precipitation extremes Ramesh S.V. Teegavarapu a,⇑ , Aneesh Goly a,1 , Jayantha Obeysekera b,2 a Department of Civil Engineering, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, United States b Hydrologic & Environmental Systems Modeling, South Florida Water Management District, 3301 Gun Club Road, West Palm Beach, FL 33406, United States article info Article history: Received 15 October 2012 Received in revised form 24 April 2013 Accepted 4 May 2013 Available online 11 May 2013 This manuscript was handled by Konstantine P. Georgakakos, Editor-in-Chief, with the assistance of Ashish Sharma, Associate Editor Keywords: Extreme precipitation Atlantic multidecadal oscillation (AMO) Bootstrap Parametric and nonparametric tests Depth–duration–frequency (DDF) curves Florida summary A major teleconnection, Atlantic multidecadal oscillation (AMO) under two phases (cool and warm) influ- encing precipitation extremes in Florida, USA, is the main focus of this study. Long-term extreme precip- itation data from several rain gages from temporal windows that coincide with the AMO phases are evaluated for changes in spatial and temporal variability across the region. Assessments of precipitation extremes for nine durations in different meteorologically homogenous rainfall areas as well as in the entire region are carried out. Methods of assessment included parametric unpaired t-tests and nonpara- metric Mann–Whitney U tests, kernel density estimates using Gaussian kernel for distribution-free com- parative analysis and bootstrap sampling-based confidence intervals. Depth-duration-frequency (DDF) curves are also developed using generalized extreme value (GEV) distributions characterizing the extremes. Analysis of data indicated increase in precipitation extremes in warm phases of AMO for dura- tions greater than 24 h. The influence of warm or cool phases of AMO on precipitation extremes is not spatially uniform in the region. Temporal shifts in occurrences of extremes from the later part of the year in warm phase to earlier in the year for the cool phase are evident. These shifts will have implications on flooding events in different regions of Florida. Magnitudes of extremes for a 25 year return period based on DDF curves were higher for all nine durations when data from cool or warm phase alone were com- pared to those obtained from data from two phases. Precipitation extremes for durations longer than a day are associated with increased landfalls of hurricanes occurring in the region in the AMO warm phases. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Characterizing of extreme precipitation events considering the magnitude, duration and location is crucial for the design and long-term operation of water resources and hydrological systems. Several studies (Cronin, 2010; Enfield et al., 2001; Lyon and Barnston, 2005; Tootle et al., 2005) have confirmed the link between teleconnections described as associations between cli- matic variations (anomalies) at distance locations (Glantz, 2001; Trimble et al., 2005), and extreme precipitation events. Some of the major teleconnections driven by coupled oceanic-atmospheric processes affecting the precipitation around the globe are: Atlantic multidecadal oscillation (AMO) (Enfield et al., 2001; Curtis, 2008), El Niño-southern oscillation (ENSO) (Ropelewski and Halpert, 1987), Pacific decadal oscillation (PDO) (Schneider and Cornuelle, 2005) and North Atlantic oscillation (NAO) (Cronin, 2010). The current study is focused on evaluating the influence of AMO on precipitation extremes at different temporal and spatial scales. AMO, a pattern of Atlantic climate variability is detected as a fluc- tuation in sea surface temperatures over the Atlantic Ocean, be- tween the Equator and Greenland. The AMO pattern was first recognized in mid-1990s (Kushnir, 1994; Schlesinger and Ram- mankutty, 1994, 1995) and named by Kerr (2000) is a long-range climatic oscillation that causes periodic changes in the surface temperature of the Atlantic Ocean, which may persist for several years or decades, usually spanning 20–40 years. AMO is suspected to be driving temperature deviations in the ocean surface that ap- pear to be driving shifts (‘‘warm’’ and ‘‘cool’’ phases) in south Flor- ida’s climate (Enfield et al., 2001). Several studies also showed the consistency between the AMO and Atlantic thermohaline circula- tion (Delworth and Mann, 2000; Knight et al., 2005; Dijkstra et al., 2006). Changes to this circulation will have impacts on pre- cipitation patterns in the Northern hemisphere (Vellinga and Wood, 2002) and bring possible changes in extreme rainfall vari- ability in Florida. 0022-1694/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhydrol.2013.05.003 ⇑ Corresponding author. Tel.: +1 (561) 297 3444. E-mail addresses: rteegava@fau.edu (R.S.V. Teegavarapu), agoly@fau.edu (A. Goly), jobey@sfwmd.gov (J. Obeysekera). 1 Tel.: +1 (561) 376 2254. 2 Tel.: +1 (561) 682 6503. Journal of Hydrology 495 (2013) 74–93 Contents lists available at SciVerse ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol