Estimated rainfall changes for the the 21st century based on
CMIP5 model scenario simulations

We applied a statistical downscaling method in order find a connection between the large-scale atmospheric circulation over the Pacific (180-120W 10S-40N) with the rainfall over Hawaii. Using observational records of precipitation at individual rainfall stations across the Hawaiian Islands, we first identified the circulation pattern that occurred during seasons with low and high precipitation at each single station during the years 1978-2007. We analyzed future climate change scenarios from 32 CMIP5 models. By means of statistical methods we were able to translate the modeled circulation changes into relative rainfall changes by measuring the similarity between the simulated circulation pattern and the composite pattern and by deploying linear regression methods. Estimated anomalies are expressed in units of % with respect to the present-day (1978-2007) seasonal mean rainfall amounts.

We looked into the future climate change scenarios from the 32 CMIP5 models using two different representative concentration pathways (RCP) 'RCP4.5' and 'RCP8.5', which represent medium and high emissions scenarios for atmospheric greenhouse gases.

We tested the linear regression results with an ANOVA F-test for their statistical significance during the calibration period 1978-2007. Stations failing the 10% significance test were excluded (marked with 'x' in the maps. As a rule of thumb, stations with correlations larger than R=0.58 between observed and regression-based rainfall anomalies were significantly correlated. Note that some of the gap-filled rainfall data had not enough observations to provide complete seasonal rainfall estimates for the calibration years. These stations were excluded from the maps.

The colored dots depict the median of downscaled seasonal precipitation anomalies obtained from 32 CMIP5 models. The downscaled rainfall anomalies were averaged over 31(29) years (2011-2041, 2041-2071, 2071-2099). The text box further shows information regarding the stations name, identification number, geographical coordinates, correlation coefficient of the calibrated regression model ("Rcal"), the mean and median of the 32 CMIP5 model downscaling results, the standard deviation in the downscaled rainfall anomalies, and the approximate 25% and 75% range of the downscaled rainfall anomalies based on the 32-member CMIP5 model ensemble.

The contours depict lines of equal annual mean rainfall amounts (climatological means 1978-2007 from the Rainfall Atlas of Hawaii. Google-Earth files retrieved from http://rainfall.geography.hawaii.edu/downloads.html in March 2013)