長期氣候變遷對長江流域暖季東移雨帶的影響與評估：以2009年5月為例

The Effects of Long-Term Climate Change on Eastward Propagating Rainfall Events over the Yangtze River Valley: Example of May 2009

張鳳茹(Feng-Ru Chang) ； 黃婉如(Wan-Ru Huang) ； 王重傑(Chung-Chieh Wang)

《大氣科學》 43卷4期 (2015/12) Pp. 265-284

摘要

觀測資料顯示，5月至7月在青藏高原東部產生的降雨，常有沿長江流域(29°N–34°N, 100°E–120°E)向東邊傳播的現象。以2009年5月為例，中國貴州、四川、與湖北省多處均發生為期一至二天的暴雨且造成災情，與東移雨帶密切相關。在全球暖化的情境下，未來此類移行性降水系統的行為將如何改變，為一重要的研究課題。為瞭解氣候變遷對長江流域東移雨帶可能造成的影響，本研究使用Weather Research and Forecasting (WRF)區域模式對2009年5月的長江流域東移雨帶進行三種不同氣候條件下的模擬。研究結果發現：(1)在原本的氣候條件下（原始情境），WRF對長江流域東移雨帶的模擬結果與觀測資料相似；(2)在加入過去氣候變異的情況下（過去情境），WRF模擬的東移雨帶個數明顯減少，東移距離明顯變短，降雨強度明顯變弱；(3)在加入未來氣候變異的情況下（未來情境），WRF模擬的東移雨帶個數、東移距離與原始情境下的模擬結果雖無明顯差異，但降雨強度則明顯變強。分析環流場的差異顯示，在過去情境下，高層西風的減弱會造成東移雨帶個數減少與東移距離變短，而水氣傳輸的減弱是造成降雨強度變弱的主因。在未來情境下，因為高層西風無明顯變化，所以東移雨帶個數與東移距離與原始情境下的模擬結果無明顯差異，而水氣傳輸的分佈則顯示，未來水氣傳輸的增強（減弱）會造成局部地區東移雨帶降雨強度變強（變弱）。

並列摘要

In this study, we use WRF model driven by three different climate conditions (the original, the past and the future) to study the effects of long-term climate change on the eastward propagating rainfall events over the Yangtze River Valley. Using May 2009 as an example, the results show that (1) under the original climate condition (i.e. Control Run), the characteristics of eastward propagating rainfall events simulated by the model are similar to the observations; (2) with the effects of past climate change (i.e. Past Run), the simulated number of propagating event is fewer; the propagating distance is shorter; and the rainfall intensity is weaker than the Control Run; (3) with the effects of future climate change (i.e. Future Run), only the rainfall intensity is noticeably stronger than the Control Run. Diagnoses on the circulation change suggest that (1) the change in upper-level westerly is responsible for the change in occurrence frequency and propagating distance of rainfall events, and (2) the change in moisture flux convergence is responsible for the change in rainfall intensity over the Yangtze River Valley.

並列關鍵字

Rainfall ； Yangtze River Valley ； Climate Change