iprc symposium on ocean salinity and global water cycle recent trends and future rainfall changes in...
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IPRC Symposium onOcean Salinity and Global
Water Cycle
Recent Trends and Future Rainfall Changes in Hawaii
Honolulu, Hawaii, 2010-08-02
Presentation by
Oliver Elison Timm
Acknowledgements:Tom Giambelluca Mami Takahashi
Henry Diaz
Latent Heat Flux from NCEP reanalysis climatologyWorld Ocean Atlas Sea Surface Salinity climatology (WOA9)
Spurious trends in globally averaged monthly mean rainfall
NCEP reanalysisERA-40 CMAP
Globally averaged monthly precipitation minus evaporation
NCEP reanalysisERA-40
Imprints of Hawaiian Islands on thehydrological cycle
NCEP reanalysis latent heat flux climatology
Imprints of Hawaiian Islands on thehydrological cycle
NCEP reanalysis latent heat flux climatologyWOA sea surface salinity
Rain-gauge observation1920-2005: recent negative trend?
•
Chu et al. (2005):PDO and ENSO have a significant influence on the rainfall amounts in Hawaii.
Recent negative trend part ofNatural variability or first sign anthropogenic forcing?
We applied statistical downscaling for the wet and dry season average rainfall:Only very weak changes
Hawaii Rainfall Index
Figures from Diaz et al. (2008)
Synoptic-Statistical Downscaling for rainfall stations in Hawaii(Timm and Diaz J. Clim., 2009)
• 134 stations• Wet and dry season average rainfall.• Selected 6 of the 23 IPCC AR4 models• Use surface meridional winds as predictors
Above average rainfall Below average rainfall
High-low composite
Statistical downscaling (SD) for rainfall stations in Hawaii(Timm and Diaz J. Clim., 2009)
• 134 stations and analyzed the • Wet and dry season average rainfall.• Selected 6 of the 23 IPCC AR4 models• Use surface meridional winds as predictors
Dry Season Wet Season
SD model: Explained Variance
Statistical downscaling for the wet and dry season average rainfall:Only very weak changes projected in the ensemble mean.
dry season wet season
Changes in the frequency of heavy rain events?
Heavy rain events:• Daily precipitation > 95% quantile in the daily rainfall distribution (wet season, 1958-1976 base period)• count the number of events in each wet season•Examine the relationship between ENSO, PNA and numbers of events •Apply Multiple Linear Regression (MLR) Number of events ~ SOI & PNAI• Analyzed 12 selected stations with daily rainfall data
SOI PNA index
MLR: Number of events
Daily rainfall data
Associated regression pattern(SOI) and PNAI
Mid 1970th climate shift
Observed changesin number of events
MLR estimated changesin number of events
Associated regression pattern(SOI) and PNAI
How will future climate changeproject onto SOI and PNA
1958-1976 and 1977-2005
Observed mid-1970th shift6 model ensemble
projected changes (SRESA1B)
IPRC Symposium onOcean Salinity and Global
Water Cycle
• Summary
– Observations show decreasing trend in mean precipitation and heavy rain events
– Attribution to anthropogenic forcing not possible yet
– ENSO and PNA explain about 20-40% of the variability in number of heavy rain events
– Future changes in ENSO-PNA:SRESA1B scenarios show no robust shifts in mean, covariance=> no significant changes is the frequency of heavy rain events
Honolulu, Hawaii, 2010-08-02
Presentation by
Oliver Elison Timm
Acknowledgements:Tom Giambelluca Mami Takahashi
Henry Diaz BUT: we do not know yet how other factors will change the frequency of heavy rain events (i.e. the unexplained part of the the variance)