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SPEArTC | Statistical Downscaling |
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Model: | Emission scenarios: | a1b a2 | Season: | Dry Wet | |
Region: | Kauai Oahu Molokai/Lanai Maui Hawaii Hawaiian Islands | Periods: |
Legend: | |
insufficient observations | Wet season is November-April |
no statistically significant estimates | Dry season is May-September |
How are the rainfall changes estimated?[+/-]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 months with low
and high precipitation at each single station during the last 50 years. In this study we only used the near surface winds. Especially, the strength and direction of the wind in north-south
direction (e.g. Trade Winds, Kona Winds) is a useful indicator for low/heavy rainfall months in many parts of the Hawaiian Islands. We looked into the future climate change scenarios from the IPCC model simulations. The wind changes were then compared with the wind pattern that have been associated with low/high monthly mean rainfall amounts of the past 50 years. By means of statistical methods we were able to estimate the projected rainfall changes by measuring the similarity among the simulated future wind changes with the past observed wind pattern during the last 50 years. |
Which emission scenario was used? [+/-]We looked into the future climate change scenarios from the IPCC model simulations. We selected the A1B emission scenario. This scenario is in the middle range
of IPCC's considered fossil fuel burning scenarios for the coming years. 6 models were analyzed for their circulation changes over the Pacific by the end of
the 21st century (2070-2099).
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Why were some stations excluded? [+/-]We carefully tested how robust the relationships between rainfall and the wind circulation over the Pacific are during the wet summer months (May-October) and the dry winter months (November-April).
This important step in the statistical downscaling excluded some stations from our further application (marked with x in the maps). Note that some stations had insufficient observations to allow for a robust statistical evaluation (marked with + in the maps).
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What do the numbers mean? [+/-]The maps show the stations and the estimated rainfall changes for the late 21st century in percent of the present average rainfall. We provide wet season (May-October) and dry season (November-April) estimates. The rainfall change is expressed in inches/month for each individual station.
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What are ensemble means? [+/-]We also provide the 'ensemble mean' changes, that is the average projected rainfall changes of all six climate models.
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What are some of the results? [+/-]For the AR4 A1B emission scenario, the six analyzed models show important changes
in the wind fields around Hawaii by the late 21st century. Two models clearly indicate opposite signs in the anomalies.
One model projects 20-30% rainfall increase over the islands; the other model suggests a rainfall decrease of about
10-20% during the wet season. It is concluded from the 6-model ensemble that the most likely scenario for Hawaii is a
5-10% reduction of the wet-season precipitation and a 5% increase during the dry season, as a result of changes in the
wind field. We discuss the sources of uncertainties in the projected rainfall changes, and consider future improvements
of the statistical downscaling work, and implications for dynamical downscaling methods.
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Please refer to the Statistical Downscaling project page for more information.
The APDRC may be acknowledged as follows: Data provided by
Asia-Pacific Data Research Center, |
Questions, Comments? |