1. 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

2. 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

3. 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

4. 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

5. Rain-producing synoptic weather types in Hawai`i (e.g. Chu, Nash and Porter, J. Climate, Vol. 6, 1457-1462, 1993.) ) Frontal system ) Kona storm ) Trade wind ) Ridge wind

6. monthly mean sea level pressure, Nov-Apr, 1970-2000 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

7. 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

8. Wind-based projected changes in seasonally averaged rainfall for Hawai`i (Timm and Diaz, J. Climate, Vol. 22, 4261-4280, 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 2070-2099 Dry season 2070-2099

9. 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

10. 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

11. Mean changes for the 12 stations Observed change SOI, PNAI estimated change black: years 1958-1976 red: years 1977-2005 1958-19761977-2005 Statistical downscaling with leading modes of climate variability: mid 1970s climate shift

12. Statistical downscaling using Southern Oscillation and Pacific North American Pattern indices: One model with emissions scenario A1B 2045-2100 Green: present day Red: 2046-2065 Purple: 2081-2100 Green: present day Red: 2046-2065 Purple: 2081-2100 12-station-mean Heavy rain events per wet season

13. Green: present day Red: 2046-2065 Purple: 2081-2100 Green: present day Red: 2046-2065 Purple: 2081-2100 Statistical downscaling using Southern Oscillation and Pacific North American Pattern indices: One model with emissions scenario A1B 2045-2100

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

15. 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

16. 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

17. 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, 1419-1444, 2007 waiting time in 2081-2100 (A1B scenario) [yr]