Influences of Atlantic multidecadal oscillation phases on spatial and temporal variability of regional precipitation extremes

- Precipitation extremes in Florida are influenced by warm and cool phases of AMO.
- Increase in extreme precipitation events in warm phase of AMO is evident.
- Influences of AMO warm phase on precipitation extremes are varied across the region.
- Temporal occurrences of extremes vary in warm to cool phases of AMO in the region.
- Extremes from one phase of AMO are higher than those from two phases.

SummaryA major teleconnection, Atlantic multidecadal oscillation (AMO) under two phases (cool and warm) influencing precipitation extremes in Florida, USA, is the main focus of this study. Long-term extreme precipitation 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 nonparametric Mann-Whitney U tests, kernel density estimates using Gaussian kernel for distribution-free comparative 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 durations 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 compared 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.