第40回 ESCセミナー
Late 21st Century Climate Change in Hawai’i Simulated with a Fine Resolution Global Model
- 日時
- 2008年7月3日（木）15:00 - 16:00
- 場所
- 横浜研究所 情報技術棟5F 大会議室
- 講演者
- Dr.Kevin Hamilton (Interim Director International Pacific Research Center University of Hawaii)
- 使用言語
- 英語
要旨
The Intergovernmental Panel on Climate Change (IPCC) recent 4th Assessment Report (AR4) provides an authoritative review of the state of climate change science. Since comprehensive global climate models (GCMs) are critical for our predictions of climate change, the AR4 reports on an extensive intercomparison of results from a number of coupled ocean-atmosphere GCMs representing the state-of-the-art.
A major limitation of the models employed in the AR4 comparisons is the horizontal resolution employed. Limitations of computational power have meant that very long GCM climate forecast integrations have generally been performed with atmospheric component models with effective horizontal grid spacings of ˜200-500 km. This is a significant issue for representing many aspects of the atmospheric circulation, but is a particular problem for Hawai’i. Hawaiian weather is strongly affected by the steep topography present on the Islands. Typical AR4 models might represent all the Hawaiian Islands as a single land grid box or even ignore Hawai’i entirely!
The Climate Research Department of the Japan Meteorological Agency’s Meteorological Research Institute (MRI) performed the standard set of AR4 runs with a version of their coupled ocean-atmosphere model run at spectral horizontal resolution T42, which corresponds to a grid spacing of about 300 km. However, the MRI group supplemented the standard runs with two special 20-year integrations of their global atmospheric model run at much higher resolution (TL959, corresponding to horizontal grid spacing of about 20 km; this version of the model also had enhanced vertical resolution with 60 numerical levels). The sea surface temperatures (SSTs) used as boundary conditions for this high resolution atmospheric model were based on those from the late 20th Century and late 21st Century coupled T42 integrations. This provides, for the first time, a global warming forecast with a global model that has a somewhat realistic representation of the coastlines and topography of the main Hawaiian Islands.
The late 20th Century and late 21st Century simulations in a variety of AR4 models and the special MRI TL959 model were examined. The low resolution models produce only modest mean rainfall over the Hawaiian region, and the response of the rainfall to global warming varies markedly among models, with some models predicting increased rainfall and others decreased rainfall. The T42 MRI model predicts significantly (˜20%) less total annual rainfall over the Hawaiian region in the late 21st Century relative to the 20th Century. The high resolution TL959 model, by contrast, produces a somewhat realistic present day rainfall simulation, particularly for the Big Island and clearly forecasts increased total rainfall in the late 21st Century for the land areas of Hawai’i. This increase in mean rainfall is welcome, of course, as Hawai’i is already straining its fresh water resources. However, the increased rainfall is accompanied by a particular increase in extreme daily rainfall events, presumably leading to more frequent flooding of low-lying areas, and exacerbating problems expected from rising global sea level.
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