極端降雨相關指標在臺灣長期變化的分析：觀測、模擬及未來推估

Abstract

根據IPCC的氣候變遷科學評估，當大氣受到暖化的影響，全球降雨型態也隨之產生改變，大部分陸地上的強降雨事件發生頻率有增加的變化，不過各地局部的變化趨勢還是有所不同。本研究以氣候變遷偵測與指標專家小組所制定的極端降雨相關指標，使用高解析度網格觀測資料，調查近60年臺灣不同季節的極端降雨特性變化；並使用兩個動力降尺度模式，分析其對於極端指標在現今氣候的模擬能力及未來變化的推估。我們發現，對於近60年的長期趨勢變化，冬季東北角極端降雨的強度跟頻率增加，且極端降雨增加的區域延伸到南部；春季則是北部降雨強度跟總降雨量增加，冬春季皆受到東北海域水氣通量輻合增強所致。梅雨季降雨天數減少，可能由於臺灣到西北太平洋一帶水氣通量輻散。颱風季臺灣附近有氣旋異常環流，南部及花蓮北部的降雨強度、大雨日數統計上顯著增加。對於現今氣候的模擬，WRF-MRI跟WRF-HiRAM在梅雨季皆和觀測資料有較低的相關係數，其餘各季的降雨指標，模式大多能模擬其空間分布。未來變化推估方面，預期春季東北部及颱風季全台降雨天數有統計上顯著的減少；梅雨季跟颱風季在西部極端降雨強度跟頻率增加。對於天數改變的原因，颱風季主要受副熱帶高壓在未來增強所致；對於極端降雨強度跟頻率的變化，則是受西南氣流增強影響。According to the IPCC, heavy rain increases in most land regions due to global warming. However, the sign of the change is different in areas. We use high-resolution gridded observation data to investigate extreme rainfall related indices from the ETCCDI during the recent 60 years in Taiwan. In addition, dynamical downscaling models are for present-day simulation and projection of extreme indices.For the long-term change, the extreme rainfall intensity and frequency have increased in the northeast area and extended to southern Taiwan in winter; the total rainfall increased over northern Taiwan in spring, with the increase in moisture flux convergence over the northeast ocean. The rainy days have decreased during the Mei-Yu season, likely due to the decrease in moisture flux convergence over Taiwan. During the typhoon season, the days of heavy rain have increased over southern Taiwan and the north area of Hualien due to the cyclonic circulation near Taiwan.For the present-day simulation, WRF-MRI and WRF-HiRAM produce lower correlation values during the Mei-Yu season but can capture the spatial distribution of other indices. For the future projections, the rainy days will decrease over northeastern Taiwan in spring and over Taiwan in the typhoon season. In the Mei-Yu and typhoon seasons, extreme rainfall will increase over western Taiwan. The change in rainy days is that the Western North Pacific subtropical high will be stronger in the future. The extreme rainfall changes are due to the enhancement of southwesterly flow.