The Science of Climate Change in Hawai‘i Statistical Downscaling of Rainfall Projections for Hawai‘i Asia Room, East-West Center, 1:30-5:00 pm January 19 & 20, 2011 Oliver Elison Timm 1 Thomas W. Giambelluca 2 Mami Takahashi 2 Henry F. Diaz 3 1 International Pacific Research Center, University of Hawaii at Manoa 2 Department of Geography, University of Hawaii at Manoa 3 Earth System Research Laboratory, CIRES, NOAA, Boulder, Colorado

Model simulation 20 th century Model simulation 21 st century projected climate anomalies Refinement process projected changes in mean rainfall projected changes in heavy rainfall projected changes in droughts From coarse-scale global climate change models to local environmental change

Model simulation 20 th century Model simulation 21 st century projected climate anomalies Statistical downscaling projected changes in mean rainfall projected changes in heavy rainfall projected changes in droughts From coarse-scale global climate change models to local environmental change

IPCC Fourth Assessment Report, 2007 precipitation change for Hawai’i: likely to decrease Models show a drier climate Models results inconsistentMost models: drier climateMost models: wetter climate No significant changeModels show a wetter climate

Rain-producing synoptic weather types in Hawai`i (e.g. Chu, Nash and Porter, J. Climate, Vol. 6, , 1993.) ) Frontal system ) Kona storm ) Trade wind ) Ridge wind

monthly mean sea level pressure, Nov-Apr, H H High PreciptationLow Preciptation How does the large-scale circulation control the local rainfall? Example for Hilo region of Big Island SLP data from ERA-40 reanalysis

How does the large- scale circulation control the local rainfall? Example for Hilo region of Big Island 9 wettest months9 driest months Difference wet-dry Regression Rainfall vs Projection Index

Wind-based projected changes in seasonally averaged rainfall for Hawai`i (Timm and Diaz, J. Climate, Vol. 22, , 2009) Histogram of the projected rainfall changes using the six-model ensemble and 134 rainfall stations Histogram of the projected rainfall changes using the six-model ensemble and 134 rainfall stations Wet season Dry season

Statistical downscaling with leading modes of climate variability: Southern Oscillation, Pacific North American pattern => number of heavy rain event per winter season 500hPa geopotential height anomaly 1000hPa geopot. height anomaly SO IndexPNA index Daily rainfall amounts at Naalehu, Big Island Heavy rain events / wet season (Nov-Apr), Naalehu, Big Island

Number of heavy rain events n n= a 0 + a 1 *SOI +a 2 *PNA Statistical downscaling with leading modes of climate variability: Southern Oscillation, Pacific North American pattern => number of heavy rain event per winter season

Mean changes for the 12 stations Observed change SOI, PNAI estimated change black: years red: years Statistical downscaling with leading modes of climate variability: mid 1970s climate shift

Statistical downscaling using Southern Oscillation and Pacific North American Pattern indices: One model with emissions scenario A1B Green: present day Red: Purple: Green: present day Red: Purple: station-mean Heavy rain events per wet season

Green: present day Red: Purple: Green: present day Red: Purple: Statistical downscaling using Southern Oscillation and Pacific North American Pattern indices: One model with emissions scenario A1B

Statistical downscaling with leading modes of climate variability: Emissions scenarios A1B A2

The Science of Climate Change in Hawai‘i Statistical Downscaling of Rainfall Projections for Hawai‘i Asia Room, East-West Center January 19 & 20, 2011 Oliver Elison Timm 1 Thomas W. Giambelluca 2 Mami Takahashi 2 Henry F. Diaz 3 ☂ large-scale circulation has strong effect on rain in Hawai`i ☂ slight increase in rainfall during dry months ☂ future climate change projections of IPPC AR4: ☂ small reduction in rainfall amounts during the wet months ☂ future trend in mean and heavy rain events still uncertain given the current IPPC AR4 future model projections. ☂ frequency of heavy rain events has decreased in last decades

Composite mean for heavy rainfall events: 700 hPa moisture transport and specific humidity Composite mean for heavy rainfall events: 700 hPa moisture transport and specific humidity Lihue Hilo

Extreme rain events with currently 20-yr return period: No significant change in waiting time in 21 st century around Hawaii (IPCC AR4 multi model average) Kharin et al., J. Climate, Vol. 20, , 2007 waiting time in (A1B scenario) [yr]